diff --git a/openbsc/.gitignore b/openbsc/.gitignore
index ca73db6..fc3d0bf 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -53,6 +53,7 @@
 src/nat/bsc_nat
 src/gprs/osmo-sgsn
 src/gprs/osmo-gbproxy
+src/gprs/osmo-gtphub
 src/osmo-bsc_nat/osmo-bsc_nat
 
 #tests
@@ -78,6 +79,7 @@
 tests/sgsn/sgsn_test
 tests/subscr/subscr_test
 tests/oap/oap_test
+tests/gtphub/gtphub_test
 
 tests/atconfig
 tests/atlocal
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 8b7ce62..098e5b4 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -210,6 +210,7 @@
     tests/sgsn/Makefile
     tests/subscr/Makefile
     tests/oap/Makefile
+    tests/gtphub/Makefile
     doc/Makefile
     doc/examples/Makefile
     Makefile)
diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 8a074c2..15c38d1 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -18,6 +18,7 @@
 		 gprs_gb_parse.h smpp.h meas_feed.h gprs_gsup_messages.h \
 		 gprs_gsup_client.h bsc_msg_filter.h \
 		 oap.h oap_messages.h
+		 gtphub.h
 
 openbsc_HEADERS = gsm_04_08.h meas_rep.h bsc_api.h
 openbscdir = $(includedir)/openbsc
diff --git a/openbsc/include/openbsc/debug.h b/openbsc/include/openbsc/debug.h
index 19d8fc2..189ca47 100644
--- a/openbsc/include/openbsc/debug.h
+++ b/openbsc/include/openbsc/debug.h
@@ -33,6 +33,7 @@
 	DCTRL,
 	DSMPP,
 	DFILTER,
+	DGTPHUB,
 	Debug_LastEntry,
 };
 
diff --git a/openbsc/include/openbsc/gtphub.h b/openbsc/include/openbsc/gtphub.h
new file mode 100644
index 0000000..5298505
--- /dev/null
+++ b/openbsc/include/openbsc/gtphub.h
@@ -0,0 +1,424 @@
+/* GTP Hub Implementation */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/socket.h>
+
+#include <osmocom/core/select.h>
+#include <osmocom/core/timer.h>
+
+
+/* support */
+
+/* TODO move to osmocom/core/socket.c ? */
+#include <netdb.h> /* for IPPROTO_* etc */
+struct osmo_sockaddr {
+	struct sockaddr_storage a;
+	socklen_t l;
+};
+
+/* TODO move to osmocom/core/socket.c ? */
+/*! \brief Initialize a sockaddr
+ * \param[out] addr  Valid osmo_sockaddr pointer to write result to
+ * \param[in] family  Address Family like AF_INET, AF_INET6, AF_UNSPEC
+ * \param[in] type  Socket type like SOCK_DGRAM, SOCK_STREAM
+ * \param[in] proto  Protocol like IPPROTO_TCP, IPPROTO_UDP
+ * \param[in] host Remote host name or IP address in string form
+ * \param[in] port Remote port number in host byte order
+ * \returns 0 on success, otherwise an error code (from getaddrinfo()).
+ *
+ * Copy the first result from a getaddrinfo() call with the given parameters to
+ * *addr and *addr_len. On error, do not change *addr and return nonzero.
+ */
+int osmo_sockaddr_init(struct osmo_sockaddr *addr,
+		       uint16_t family, uint16_t type, uint8_t proto,
+		       const char *host, uint16_t port);
+
+/* Conveniently pass AF_UNSPEC, SOCK_DGRAM and IPPROTO_UDP to
+ * osmo_sockaddr_init(). */
+static inline int osmo_sockaddr_init_udp(struct osmo_sockaddr *addr,
+					 const char *host, uint16_t port)
+{
+	return osmo_sockaddr_init(addr, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, host, port);
+}
+
+/*! \brief convert sockaddr to human readable string.
+ * \param[out] addr_str  Valid pointer to a buffer of length addr_str_len.
+ * \param[in] addr_str_len  Size of buffer addr_str points at.
+ * \param[out] port_str  Valid pointer to a buffer of length port_str_len.
+ * \param[in] port_str_len  Size of buffer port_str points at.
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \param[in] flags  flags as passed to getnameinfo().
+ * \returns  0 on success, an error code on error.
+ *
+ * Return the IPv4 or IPv6 address string and the port (a.k.a. service) string
+ * representations of the given struct osmo_sockaddr in two caller provided
+ * char buffers. Flags of (NI_NUMERICHOST | NI_NUMERICSERV) return numeric
+ * address and port. Either one of addr_str or port_str may be NULL, in which
+ * case nothing is returned there.
+ *
+ * See also osmo_sockaddr_to_str() (less flexible, but much more convenient). */
+int osmo_sockaddr_to_strs(char *addr_str, size_t addr_str_len,
+			  char *port_str, size_t port_str_len,
+			  const struct osmo_sockaddr *addr,
+			  int flags);
+
+
+/*! \brief conveniently concatenate the parts returned by osmo_sockaddr_to_strs().
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \param[in] buf  A buffer to use for string operations.
+ * \param[in] buf_len  Length of the buffer.
+ * \returns  Address string (in buffer).
+ *
+ * Compose a string of the numeric IP-address and port represented by *addr of
+ * the form "<ip-addr> port <port>". The returned string is valid until the
+ * next invocation of this function.
+ */
+const char *osmo_sockaddr_to_strb(const struct osmo_sockaddr *addr,
+				  char *buf, size_t buf_len);
+
+/*! \brief conveniently return osmo_sockaddr_to_strb() in a static buffer.
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \returns  Address string in static buffer.
+ *
+ * See osmo_sockaddr_to_strb().
+ *
+ * Note: only one osmo_sockaddr_to_str() call will work per print/log
+ * statement. For two or more, use osmo_sockaddr_to_strb() with a separate
+ * buffer each.
+ */
+const char *osmo_sockaddr_to_str(const struct osmo_sockaddr *addr);
+
+/*! \brief compare two osmo_sockaddr.
+ * \param[in] a  The first address to compare.
+ * \param[in] b  The other address to compare.
+ * \returns 0 if equal, otherwise -1 or 1.
+ */
+int osmo_sockaddr_cmp(const struct osmo_sockaddr *a, const struct osmo_sockaddr *b);
+
+/*! \brief Overwrite *dst with *src.
+ * Like memcpy(), but copy only the valid bytes. */
+void osmo_sockaddr_copy(struct osmo_sockaddr *dst, const struct osmo_sockaddr *src);
+
+
+/* general */
+
+enum gtphub_plane_idx {
+	GTPH_PLANE_CTRL = 0,
+	GTPH_PLANE_USER = 1,
+	GTPH_PLANE_N
+};
+
+extern const char* const gtphub_plane_idx_names[GTPH_PLANE_N];
+extern const uint16_t gtphub_plane_idx_default_port[GTPH_PLANE_N];
+
+/* A host address in the form that is expected in the 7.7.32 GSN Address IE.
+ * len is either 4 (IPv4) or 16 (IPv6), any other value is invalid. If no
+ * address is set, len shall be 0. */
+struct gsn_addr {
+	uint16_t len;
+	uint8_t buf[16];
+};
+
+void gsn_addr_copy(struct gsn_addr *gsna, const struct gsn_addr *src);
+int gsn_addr_from_str(struct gsn_addr *gsna, const char *numeric_addr_str);
+
+/* Return gsna in numeric string form, in a static buffer. */
+const char *gsn_addr_to_str(const struct gsn_addr *gsna);
+
+/* note: strbuf_len doesn't need to be larger than INET6_ADDRSTRLEN + 1. */
+const char *gsn_addr_to_strb(const struct gsn_addr *gsna,
+			     char *strbuf, int strbuf_len);
+
+/* Return 1 on match, zero otherwise. */
+int gsn_addr_same(const struct gsn_addr *a, const struct gsn_addr *b);
+
+
+/* expiry */
+
+struct expiring_item;
+typedef void (*del_cb_t)(struct expiring_item *);
+
+struct expiring_item {
+	struct llist_head entry;
+	time_t expiry;
+	del_cb_t del_cb;
+};
+
+struct expiry {
+	int expiry_in_seconds;
+	struct llist_head items;
+};
+
+/* Initialize an expiry queue. */
+void expiry_init(struct expiry *exq, int expiry_in_seconds);
+
+/* Add a new mapping, or restart the expiry timeout for an already listed mapping. */
+void expiry_add(struct expiry *exq, struct expiring_item *mapping, time_t now);
+
+/* Remove the given item from its expiry queue, and call item->del_cb, if set.
+ * This sets item->del_cb to NULL and is harmless when run a second time on the
+ * same item, so the del_cb may choose to call this function, too, to allow
+ * deleting items from several code paths. */
+void expiring_item_del(struct expiring_item *item);
+
+/* Carry out due expiry of mappings. Must be invoked regularly.
+ * 'now' is the current clock count in seconds and must correspond to the clock
+ * count passed to nr_map_add(). A monotonous clock counter should be used. */
+int expiry_tick(struct expiry *exq, time_t now);
+
+
+/* number map */
+
+/* A number map assigns a "random" mapped number to each user provided number.
+ * If the same number is requested multiple times, the same mapped number is
+ * returned.
+ *
+ * Number maps plug into possibly shared pools and expiry queues, for example:
+ *
+ *     mapA -----------+-> pool1           <-+-- mapB
+ *     {10->1, 11->5}  |   {1, 2, 3, ...}    |   {10->2, 11->3}
+ *                     |                     |
+ *                     |                     |
+ *                 /-> \-> expiry1         <-/
+ *                 |       (30 seconds)
+ *                 |
+ *     mapC -------+-----> pool2           <-+-- mapD
+ *     {10->1, 11->3}      {1, 2, 3, ...}    |   {10->2, 11->5}
+ *                                           |
+ *                         expiry2         <-/
+ *                         (60 seconds)
+ *
+ * A map contains mappings ("10->1"). Each map needs a number pool, which can
+ * be shared with other maps. Each new mapping receives a number from the pool,
+ * which is then unavailable to any other map using the same pool.
+ *
+ * A map may point at an expiry queue, in which case all mappings added to it
+ * are also appended to the expiry queue (using a separate llist entry in the
+ * mapping). Any number of maps may submit to the same expiry queue, if they
+ * desire the same expiry timeout. An expiry queue stores the mappings in
+ * chronological order, so that expiry checking is needed only from the start
+ * of the queue; hence only mappings with identical expiry timeout can be added
+ * to the same expiry queue. Upon expiry, a mapping is dropped from the map it
+ * was submitted at. expiry_tick() needs to be called regularly for each expiry
+ * queue.
+ *
+ * A nr_mapping can be embedded in a larger struct: each mapping can have a
+ * distinct destructor (del_cb), and each del_cb can figure out the container
+ * struct's address and free that upon expiry or manual deletion. So in expiry
+ * queues (and even maps), mappings of different container types can be mixed.
+ * This can help to drastically reduce the amount of unnecessary visits during
+ * expiry checking, for the case that no expiry is pending. An expiry queue
+ * always knows which mappings to expire next, because they are right at the
+ * start of its list.
+ *
+ * Mapping allocation and a del_cb are provided by the caller. If del_cb is
+ * NULL, no deallocation will be done (allowing statically allocated entries).
+ */
+/* TODO at some point I thought the allocation & del_cb complexity was
+ * needed/helpful, but by now it seems like overkill. Maybe lose that again. */
+
+typedef int nr_t;
+
+/* Generator for unused numbers. So far this counts upwards from zero, but the
+ * implementation may change in the future. Treat this like an opaque struct.
+ * If this becomes random, the tests need to be fixed. */
+struct nr_pool {
+	nr_t last_nr;
+	/* TODO add min, max, for safe wrapping */
+};
+
+struct nr_mapping {
+	struct llist_head entry;
+	struct expiring_item expiry_entry;
+
+	void *origin;
+	nr_t orig;
+	nr_t repl;
+};
+
+struct nr_map {
+	struct nr_pool *pool; /* multiple nr_maps can share a nr_pool. */
+	struct expiry *add_items_to_expiry;
+	struct llist_head mappings;
+};
+
+
+void nr_pool_init(struct nr_pool *pool);
+
+/* Return the next unused number from the nr_pool. */
+nr_t nr_pool_next(struct nr_pool *pool);
+
+/* Initialize the nr_mapping to zero/empty values. */
+void nr_mapping_init(struct nr_mapping *mapping);
+
+/* Remove the given mapping from its parent map and expiry queue, and call
+ * mapping->del_cb, if set. */
+void nr_mapping_del(struct nr_mapping *mapping);
+
+/* Initialize an (already allocated) nr_map, and set the map's number pool.
+ * Multiple nr_map instances may use the same nr_pool. Set the nr_map's expiry
+ * queue to exq, so that all added mappings are automatically expired after the
+ * time configured in exq. exq may be NULL to disable automatic expiry. */
+void nr_map_init(struct nr_map *map, struct nr_pool *pool,
+		 struct expiry *exq);
+
+/* Add a new entry to the map. mapping->orig, mapping->origin and
+ * mapping->del_cb must be set before calling this function. The remaining
+ * fields of *mapping will be overwritten. mapping->repl is set to the next
+ * available mapped number from map->pool. 'now' is the current clock count in
+ * seconds; if no map->expiry is used, just pass 0 for 'now'. */
+void nr_map_add(struct nr_map *map, struct nr_mapping *mapping,
+		time_t now);
+
+/* Return a known mapping from nr_orig and the given origin. If nr_orig is
+ * unknown, return NULL. */
+struct nr_mapping *nr_map_get(const struct nr_map *map,
+			      void *origin, nr_t nr_orig);
+
+/* Return a known mapping to nr_repl. If nr_repl is unknown, return NULL. */
+struct nr_mapping *nr_map_get_inv(const struct nr_map *map, nr_t nr_repl);
+
+/* Remove all mappings from map. */
+void nr_map_clear(struct nr_map *map);
+
+/* Return 1 if map has no entries, 0 otherwise. */
+int nr_map_empty(const struct nr_map *map);
+
+
+/* config */
+
+static const int GTPH_SEQ_MAPPING_EXPIRY_SECS = 30; /* TODO is there a spec for this? */
+static const int GTPH_TEI_MAPPING_EXPIRY_MINUTES = 6 * 60; /* TODO is there a spec for this? */
+
+struct gtphub_cfg_addr {
+	const char *addr_str;
+	uint16_t port;
+};
+
+struct gtphub_cfg_bind {
+	struct gtphub_cfg_addr bind;
+};
+
+struct gtphub_cfg {
+	struct gtphub_cfg_bind to_sgsns[GTPH_PLANE_N];
+	struct gtphub_cfg_bind to_ggsns[GTPH_PLANE_N];
+	struct gtphub_cfg_addr sgsn_proxy[GTPH_PLANE_N];
+	struct gtphub_cfg_addr ggsn_proxy[GTPH_PLANE_N];
+};
+
+
+/* state */
+
+struct gtphub_peer {
+	struct llist_head entry;
+
+	struct llist_head addresses; /* Alternatives, not load balancing. */
+	struct nr_pool seq_pool;
+	struct nr_map seq_map;
+};
+
+struct gtphub_peer_addr {
+	struct llist_head entry;
+
+	struct gtphub_peer *peer;
+	struct gsn_addr addr;
+	struct llist_head ports;
+};
+
+struct gtphub_peer_port {
+	struct llist_head entry;
+
+	struct gtphub_peer_addr *peer_addr;
+	uint16_t port;
+	unsigned int ref_count; /* references from other peers' seq_maps */
+	struct osmo_sockaddr sa;
+};
+
+struct gtphub_bind {
+	struct gsn_addr local_addr;
+	struct osmo_fd ofd;
+
+	/* list of struct gtphub_peer */
+	struct llist_head peers;
+};
+
+struct gtphub {
+	struct gtphub_bind to_sgsns[GTPH_PLANE_N];
+	struct gtphub_bind to_ggsns[GTPH_PLANE_N];
+
+	/* pointers to an entry of to_sgsns[x].peers */
+	struct gtphub_peer_port *sgsn_proxy[GTPH_PLANE_N];
+
+	/* pointers to an entry of to_ggsns[x].peers */
+	struct gtphub_peer_port *ggsn_proxy[GTPH_PLANE_N];
+
+	struct nr_map tei_map[GTPH_PLANE_N];
+	struct nr_pool tei_pool[GTPH_PLANE_N];
+
+	struct osmo_timer_list gc_timer;
+	struct expiry expire_seq_maps;
+	struct expiry expire_tei_maps;
+};
+
+struct gtp_packet_desc;
+
+
+/* api */
+
+int gtphub_vty_init(void);
+int gtphub_cfg_read(struct gtphub_cfg *cfg, const char *config_file);
+
+/* Initialize and start gtphub: bind to ports, run expiry timers. */
+int gtphub_start(struct gtphub *hub, struct gtphub_cfg *cfg);
+
+time_t gtphub_now(void);
+
+/* Remove expired items, empty peers, ... */
+void gtphub_gc(struct gtphub *hub, time_t now);
+
+/* Return the string of the first address for this peer. */
+const char *gtphub_peer_str(struct gtphub_peer *peer);
+/* Same with a different static buffer. We often want to print two peers. */
+const char *gtphub_peer_str2(struct gtphub_peer *peer);
+
+int gtphub_from_sgsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 time_t now,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr *to_addr);
+
+int gtphub_from_ggsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 time_t now,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr *to_addr);
+
+struct gtphub_peer_port *gtphub_port_find_sa(const struct gtphub_bind *bind,
+					     const struct osmo_sockaddr *addr);
diff --git a/openbsc/include/openbsc/vty.h b/openbsc/include/openbsc/vty.h
index 818a20e..bc30e23 100644
--- a/openbsc/include/openbsc/vty.h
+++ b/openbsc/include/openbsc/vty.h
@@ -36,6 +36,7 @@
 	BSC_NODE,
 	SMPP_NODE,
 	SMPP_ESME_NODE,
+	GTPHUB_NODE,
 };
 
 extern int bsc_vty_is_config_node(struct vty *vty, int node);
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index c8e3696..0dd38f9 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -11,6 +11,7 @@
 bin_PROGRAMS = osmo-gbproxy
 
 if HAVE_LIBGTP
+bin_PROGRAMS += osmo-gtphub
 if HAVE_LIBCARES
 bin_PROGRAMS += osmo-sgsn
 endif
@@ -33,3 +34,8 @@
 			$(top_builddir)/src/libcommon/libcommon.a \
 			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) \
 			$(LIBCRYPTO_LIBS) -lrt
+
+osmo_gtphub_SOURCES =	gtphub_main.c gtphub.c gtphub_ext.c gtphub_vty.c
+osmo_gtphub_LDADD = 	\
+			$(top_builddir)/src/libcommon/libcommon.a \
+			-lgtp $(LIBOSMOCORE_LIBS) $(LIBOSMOVTY_LIBS) -lrt
diff --git a/openbsc/src/gprs/gtphub.c b/openbsc/src/gprs/gtphub.c
new file mode 100644
index 0000000..440f00f
--- /dev/null
+++ b/openbsc/src/gprs/gtphub.c
@@ -0,0 +1,2080 @@
+/* GTP Hub Implementation */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <time.h>
+#include <limits.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <gtp.h>
+#include <gtpie.h>
+
+#include <openbsc/gtphub.h>
+#include <openbsc/debug.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/socket.h>
+
+#define GTPHUB_DEBUG 1
+
+static const int GTPH_GC_TICK_SECONDS = 1;
+
+void *osmo_gtphub_ctx;
+
+#define LOGERR(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_ERROR, fmt, ##args)
+
+#define LOG(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_NOTICE, fmt, ##args)
+
+#define ZERO_STRUCT(struct_pointer) memset(struct_pointer, '\0', sizeof(*(struct_pointer)))
+
+/* TODO move this to osmocom/core/select.h ? */
+typedef int (*osmo_fd_cb_t)(struct osmo_fd *fd, unsigned int what);
+
+/* TODO move this to osmocom/core/linuxlist.h ? */
+#define __llist_first(head) (((head)->next == (head)) ? NULL : (head)->next)
+#define llist_first(head, type, entry) llist_entry(__llist_first(head), type, entry)
+
+/* TODO move GTP header stuff to openggsn/gtp/ ? See gtp_decaps*() */
+
+enum gtp_rc {
+	GTP_RC_UNKNOWN = 0,
+	GTP_RC_TINY = 1,    /* no IEs (like ping/pong) */
+	GTP_RC_PDU = 2,     /* a real packet with IEs */
+
+	GTP_RC_TOOSHORT = -1,
+	GTP_RC_UNSUPPORTED_VERSION = -2,
+	GTP_RC_INVALID_IE = -3,
+};
+
+struct gtp_packet_desc {
+	union gtp_packet *data;
+	int data_len;
+	int header_len;
+	int version;
+	uint8_t type;
+	uint16_t seq;
+	uint32_t header_tei;
+	int rc; /* enum gtp_rc */
+	unsigned int plane_idx;
+	union gtpie_member *ie[GTPIE_SIZE];
+};
+
+void gsn_addr_copy(struct gsn_addr *gsna, const struct gsn_addr *src)
+{
+	memcpy(gsna, src, sizeof(struct gsn_addr));
+}
+
+/* Decode sa to gsna. Return 0 on success. If port is non-NULL, the port number
+ * from sa is also returned. */
+int gsn_addr_from_sockaddr(struct gsn_addr *gsna, uint16_t *port,
+			   const struct osmo_sockaddr *sa)
+{
+	char addr_str[256];
+	char port_str[6];
+
+	if (osmo_sockaddr_to_strs(addr_str, sizeof(addr_str),
+				  port_str, sizeof(port_str),
+				  sa, (NI_NUMERICHOST | NI_NUMERICSERV))
+	    != 0) {
+		return -1;
+	}
+
+	if (port)
+		*port = atoi(port_str);
+
+	return gsn_addr_from_str(gsna, addr_str);
+}
+
+int gsn_addr_from_str(struct gsn_addr *gsna, const char *numeric_addr_str)
+{
+	int af = AF_INET;
+	gsna->len = 4;
+	const char *pos = numeric_addr_str;
+	for (; *pos; pos++) {
+		if (*pos == ':') {
+			af = AF_INET6;
+			gsna->len = 16;
+			break;
+		}
+	}
+
+	int rc = inet_pton(af, numeric_addr_str, gsna->buf);
+	if (rc != 1) {
+		LOGERR("Cannot resolve numeric address: '%s'\n", numeric_addr_str);
+		return -1;
+	}
+	return 0;
+}
+
+const char *gsn_addr_to_str(const struct gsn_addr *gsna)
+{
+	static char buf[INET6_ADDRSTRLEN + 1];
+	return gsn_addr_to_strb(gsna, buf, sizeof(buf));
+}
+
+const char *gsn_addr_to_strb(const struct gsn_addr *gsna,
+			     char *strbuf,
+			     int strbuf_len)
+{
+	int af;
+	switch (gsna->len) {
+	case 4:
+		af = AF_INET;
+		break;
+	case 16:
+		af = AF_INET6;
+		break;
+	default:
+		return NULL;
+	}
+
+	const char *r = inet_ntop(af, gsna->buf, strbuf, strbuf_len);
+	if (!r) {
+		LOGERR("Cannot convert gsn_addr to string: %s: len=%d, buf=%s\n",
+		       strerror(errno),
+		       (int)gsna->len,
+		       osmo_hexdump(gsna->buf, sizeof(gsna->buf)));
+	}
+	return r;
+}
+
+int gsn_addr_same(const struct gsn_addr *a, const struct gsn_addr *b)
+{
+	if (a == b)
+		return 1;
+	if ((!a) || (!b))
+		return 0;
+	if (a->len != b->len)
+		return 0;
+	return (memcmp(a->buf, b->buf, a->len) == 0)? 1 : 0;
+}
+
+static int gsn_addr_get(struct gsn_addr *gsna, const struct gtp_packet_desc *p, int idx)
+{
+	if (p->rc != GTP_RC_PDU)
+		return -1;
+
+	unsigned int len;
+	/* gtpie.h fails to declare gtpie_gettlv()'s first arg as const. */
+	if (gtpie_gettlv((union gtpie_member**)p->ie, GTPIE_GSN_ADDR, idx,
+			 &len, gsna->buf, sizeof(gsna->buf))
+	    != 0)
+		return -1;
+	gsna->len = len;
+	return 0;
+}
+
+static int gsn_addr_put(const struct gsn_addr *gsna, struct gtp_packet_desc *p, int idx)
+{
+	if (p->rc != GTP_RC_PDU)
+		return -1;
+
+	int ie_idx;
+	ie_idx = gtpie_getie(p->ie, GTPIE_GSN_ADDR, idx);
+
+	if (ie_idx < 0)
+		return -1;
+
+	struct gtpie_tlv *ie = &p->ie[ie_idx]->tlv;
+	int ie_l = ntoh16(ie->l);
+	if (ie_l != gsna->len) {
+		LOG("Not implemented: replace an IE address of different size:"
+		    " replace %d with %d\n", (int)ie_l, (int)gsna->len);
+		return -1;
+	}
+
+	memcpy(ie->v, gsna->buf, (int)ie_l);
+	return 0;
+}
+
+/* Validate GTP version 0 data; analogous to validate_gtp1_header(), see there.
+ */
+void validate_gtp0_header(struct gtp_packet_desc *p)
+{
+	const struct gtp0_header *pheader = &(p->data->gtp0.h);
+	p->rc = GTP_RC_UNKNOWN;
+	p->header_len = 0;
+
+	OSMO_ASSERT(p->data_len >= 1);
+	OSMO_ASSERT(p->version == 0);
+
+	if (p->data_len < GTP0_HEADER_SIZE) {
+		LOGERR("GTP0 packet too short: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->type = ntoh8(pheader->type);
+	p->seq = ntoh16(pheader->seq);
+	p->header_tei = 0; /* TODO */
+
+	if (p->data_len == GTP0_HEADER_SIZE) {
+		p->rc = GTP_RC_TINY;
+		p->header_len = GTP0_HEADER_SIZE;
+		return;
+	}
+
+	/* Check packet length field versus length of packet */
+	if (p->data_len != (ntoh16(pheader->length) + GTP0_HEADER_SIZE)) {
+		LOGERR("GTP packet length field (%d + %d) does not match"
+		       " actual length (%d)\n",
+		       GTP0_HEADER_SIZE, (int)ntoh16(pheader->length),
+		       p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	LOG("GTP v0 TID = %" PRIu64 "\n", pheader->tid);
+	p->header_len = GTP0_HEADER_SIZE;
+	p->rc = GTP_RC_PDU;
+}
+
+/* Validate GTP version 1 data, and update p->rc with the result, as well as
+ * p->header_len in case of a valid header. */
+void validate_gtp1_header(struct gtp_packet_desc *p)
+{
+	const struct gtp1_header_long *pheader = &(p->data->gtp1l.h);
+	p->rc = GTP_RC_UNKNOWN;
+	p->header_len = 0;
+
+	OSMO_ASSERT(p->data_len >= 1);
+	OSMO_ASSERT(p->version == 1);
+
+	if ((p->data_len < GTP1_HEADER_SIZE_LONG)
+	    && (p->data_len != GTP1_HEADER_SIZE_SHORT)){
+		LOGERR("GTP packet too short: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->type = ntoh8(pheader->type);
+	p->header_tei = ntoh32(pheader->tei);
+	p->seq = ntoh16(pheader->seq);
+
+	LOG("|GTPv1\n");
+	LOG("| type = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    p->type, p->type);
+	LOG("| length = %" PRIu16 " 0x%04" PRIx16 "\n",
+	    ntoh16(pheader->length), ntoh16(pheader->length));
+	LOG("| TEI = %" PRIu32 " 0x%08" PRIx32 "\n",
+	    p->header_tei, p->header_tei);
+	LOG("| seq = %" PRIu16 " 0x%04" PRIx16 "\n",
+	    p->seq, p->seq);
+	LOG("| npdu = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    pheader->npdu, pheader->npdu);
+	LOG("| next = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    pheader->next, pheader->next);
+
+	if (p->data_len <= GTP1_HEADER_SIZE_LONG) {
+		p->rc = GTP_RC_TINY;
+		p->header_len = GTP1_HEADER_SIZE_SHORT;
+		return;
+	}
+
+	/* Check packet length field versus length of packet */
+	if (p->data_len != (ntoh16(pheader->length) + GTP1_HEADER_SIZE_SHORT)) {
+		LOGERR("GTP packet length field (%d + %d) does not match"
+		       " actual length (%d)\n",
+		       GTP1_HEADER_SIZE_SHORT, (int)ntoh16(pheader->length),
+		       p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->rc = GTP_RC_PDU;
+	p->header_len = GTP1_HEADER_SIZE_LONG;
+}
+
+/* Examine whether p->data of size p->data_len has a valid GTP header. Set
+ * p->version, p->rc and p->header_len. On error, p->rc <= 0 (see enum
+ * gtp_rc). p->data must point at a buffer with p->data_len set. */
+void validate_gtp_header(struct gtp_packet_desc *p)
+{
+	p->rc = GTP_RC_UNKNOWN;
+
+	/* Need at least 1 byte in order to check version */
+	if (p->data_len < 1) {
+		LOGERR("Discarding packet - too small: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->version = p->data->flags >> 5;
+
+	switch (p->version) {
+	case 0:
+		validate_gtp0_header(p);
+		break;
+	case 1:
+		validate_gtp1_header(p);
+		break;
+	default:
+		LOGERR("Unsupported GTP version: %d\n", p->version);
+		p->rc = GTP_RC_UNSUPPORTED_VERSION;
+		break;
+	}
+}
+
+
+/* Return the value of the i'th IMSI IEI by copying to *imsi.
+ * The first IEI is reached by passing i = 0.
+ * imsi must point at allocated space of (at least) 8 bytes.
+ * Return 1 on success, or 0 if not found. */
+static int get_ie_imsi(union gtpie_member *ie[], uint8_t *imsi, int i)
+{
+	return gtpie_gettv0(ie, GTPIE_IMSI, i, imsi, 8) == 0;
+}
+
+/* Analogous to get_ie_imsi(). nsapi must point at a single uint8_t. */
+static int get_ie_nsapi(union gtpie_member *ie[], uint8_t *nsapi, int i)
+{
+	return gtpie_gettv1(ie, GTPIE_NSAPI, i, nsapi) == 0;
+}
+
+static char imsi_digit_to_char(uint8_t nibble)
+{
+	nibble &= 0x0f;
+	if (nibble > 9)
+		return (nibble == 0x0f) ? '\0' : '?';
+	return '0' + nibble;
+}
+
+/* Return a human readable IMSI string, in a static buffer.
+ * imsi must point at 8 octets of IMSI IE encoded IMSI data. */
+static const char *imsi_to_str(uint8_t *imsi)
+{
+	static char str[17];
+	int i;
+
+	for (i = 0; i < 8; i++) {
+		str[2*i] = imsi_digit_to_char(imsi[i]);
+		str[2*i + 1] = imsi_digit_to_char(imsi[i] >> 4);
+	}
+	str[16] = '\0';
+	return str;
+}
+
+/* Validate header, and index information elements. Write decoded packet
+ * information to *res. res->data will point at the given data buffer. On
+ * error, p->rc is set <= 0 (see enum gtp_rc). */
+static void gtp_decode(const uint8_t *data, int data_len,
+		       unsigned int from_plane_idx,
+		       struct gtp_packet_desc *res)
+{
+	ZERO_STRUCT(res);
+	res->data = (union gtp_packet*)data;
+	res->data_len = data_len;
+	res->plane_idx = from_plane_idx;
+
+	validate_gtp_header(res);
+
+	if (res->rc <= 0) {
+		LOGERR("INVALID: dropping GTP packet.\n");
+		return;
+	}
+
+	LOG("Valid GTP header (v%d)\n", res->version);
+
+	if (res->rc != GTP_RC_PDU) {
+		LOG("no IEs in this GTP packet\n");
+		return;
+	}
+
+	if (gtpie_decaps(res->ie, res->version,
+			 (void*)(data + res->header_len),
+			 res->data_len - res->header_len) != 0) {
+		res->rc = GTP_RC_INVALID_IE;
+		return;
+	}
+
+#if GTPHUB_DEBUG
+	int i;
+
+	for (i = 0; i < 10; i++) {
+		uint8_t imsi[8];
+		if (!get_ie_imsi(res->ie, imsi, i))
+			break;
+		LOG("| IMSI %s\n", imsi_to_str(imsi));
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint8_t nsapi;
+		if (!get_ie_nsapi(res->ie, &nsapi, i))
+			break;
+		LOG("| NSAPI %d\n", (int)nsapi);
+	}
+
+	for (i = 0; i < 2; i++) {
+		struct gsn_addr addr;
+		if (gsn_addr_get(&addr, res, i) == 0)
+			LOG("| addr %s\n", gsn_addr_to_str(&addr));
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint32_t tei;
+		if (gtpie_gettv4(res->ie, GTPIE_TEI_DI, i, &tei) != 0)
+			break;
+		LOG("| TEI DI (USER) %" PRIu32 " 0x%08" PRIx32 "\n",
+		    tei, tei);
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint32_t tei;
+		if (gtpie_gettv4(res->ie, GTPIE_TEI_C, i, &tei) != 0)
+			break;
+		LOG("| TEI (CTRL) %" PRIu32 " 0x%08" PRIx32 "\n",
+		    tei, tei);
+	}
+#endif
+}
+
+
+/* expiry */
+
+void expiry_init(struct expiry *exq, int expiry_in_seconds)
+{
+	ZERO_STRUCT(exq);
+	exq->expiry_in_seconds = expiry_in_seconds;
+	INIT_LLIST_HEAD(&exq->items);
+}
+
+void expiry_add(struct expiry *exq, struct expiring_item *item, time_t now)
+{
+	item->expiry = now + exq->expiry_in_seconds;
+
+	/* Add/move to the tail to always sort by expiry, ascending. */
+	llist_del(&item->entry);
+	llist_add_tail(&item->entry, &exq->items);
+}
+
+int expiry_tick(struct expiry *exq, time_t now)
+{
+	int expired = 0;
+	struct expiring_item *m, *n;
+	llist_for_each_entry_safe(m, n, &exq->items, entry) {
+		if (m->expiry <= now) {
+			expiring_item_del(m);
+			expired ++;
+		} else {
+			LOG("Not expired: %d > %d\n", (int)m->expiry, (int)now);
+			/* The items are added sorted by expiry. So when we hit
+			 * an unexpired entry, only more unexpired ones will
+			 * follow. */
+			break;
+		}
+	}
+	return expired;
+}
+
+void expiring_item_init(struct expiring_item *item)
+{
+	ZERO_STRUCT(item);
+	INIT_LLIST_HEAD(&item->entry);
+}
+
+void expiring_item_del(struct expiring_item *item)
+{
+	OSMO_ASSERT(item);
+	llist_del(&item->entry);
+	INIT_LLIST_HEAD(&item->entry);
+	if (item->del_cb) {
+		/* avoid loops */
+		del_cb_t del_cb = item->del_cb;
+		item->del_cb = 0;
+		(del_cb)(item);
+	}
+}
+
+
+/* nr_map, nr_pool */
+
+void nr_pool_init(struct nr_pool *pool)
+{
+	*pool = (struct nr_pool){};
+}
+
+nr_t nr_pool_next(struct nr_pool *pool)
+{
+	pool->last_nr ++;
+
+	OSMO_ASSERT(pool->last_nr > 0);
+	/* TODO: gracefully handle running out of TEIs. */
+	/* TODO: random TEIs. */
+
+	return pool->last_nr;
+}
+
+void nr_map_init(struct nr_map *map, struct nr_pool *pool,
+		 struct expiry *exq)
+{
+	ZERO_STRUCT(map);
+	map->pool = pool;
+	map->add_items_to_expiry = exq;
+	INIT_LLIST_HEAD(&map->mappings);
+}
+
+void nr_mapping_init(struct nr_mapping *m)
+{
+	ZERO_STRUCT(m);
+	INIT_LLIST_HEAD(&m->entry);
+	expiring_item_init(&m->expiry_entry);
+}
+
+void nr_map_add(struct nr_map *map, struct nr_mapping *mapping, time_t now)
+{
+	/* Generate a mapped number */
+	mapping->repl = nr_pool_next(map->pool);
+
+	/* Add to the tail to always yield a list sorted by expiry, in
+	 * ascending order. */
+	llist_add_tail(&mapping->entry, &map->mappings);
+	if (map->add_items_to_expiry)
+		expiry_add(map->add_items_to_expiry,
+			   &mapping->expiry_entry,
+			   now);
+}
+
+void nr_map_clear(struct nr_map *map)
+{
+	struct nr_mapping *m;
+	struct nr_mapping *n;
+	llist_for_each_entry_safe(m, n, &map->mappings, entry) {
+		nr_mapping_del(m);
+	}
+}
+
+int nr_map_empty(const struct nr_map *map)
+{
+	return llist_empty(&map->mappings);
+}
+
+struct nr_mapping *nr_map_get(const struct nr_map *map,
+			      void *origin, nr_t nr_orig)
+{
+	struct nr_mapping *mapping;
+	llist_for_each_entry(mapping, &map->mappings, entry) {
+		if ((mapping->origin == origin)
+		    && (mapping->orig == nr_orig))
+			return mapping;
+	}
+	/* Not found. */
+	return NULL;
+}
+
+struct nr_mapping *nr_map_get_inv(const struct nr_map *map, nr_t nr_repl)
+{
+	struct nr_mapping *mapping;
+	llist_for_each_entry(mapping, &map->mappings, entry) {
+		if (mapping->repl == nr_repl) {
+			return mapping;
+		}
+	}
+	/* Not found. */
+	return NULL;
+}
+
+void nr_mapping_del(struct nr_mapping *mapping)
+{
+	OSMO_ASSERT(mapping);
+	llist_del(&mapping->entry);
+	INIT_LLIST_HEAD(&mapping->entry);
+	expiring_item_del(&mapping->expiry_entry);
+}
+
+
+/* gtphub */
+
+const char* const gtphub_plane_idx_names[GTPH_PLANE_N] = {
+	"CTRL",
+	"USER",
+};
+
+const uint16_t gtphub_plane_idx_default_port[GTPH_PLANE_N] = {
+	2123,
+	2152,
+};
+
+time_t gtphub_now(void)
+{
+	struct timespec now_tp;
+	OSMO_ASSERT(clock_gettime(CLOCK_MONOTONIC, &now_tp) >= 0);
+	return now_tp.tv_sec;
+}
+
+/* Remove a gtphub_peer from its list and free it. */
+static void gtphub_peer_del(struct gtphub_peer *peer)
+{
+	nr_map_clear(&peer->seq_map);
+	llist_del(&peer->entry);
+	talloc_free(peer);
+}
+
+static void gtphub_peer_addr_del(struct gtphub_peer_addr *pa)
+{
+	OSMO_ASSERT(llist_empty(&pa->ports));
+	llist_del(&pa->entry);
+	talloc_free(pa);
+}
+
+static void gtphub_peer_port_del(struct gtphub_peer_port *pp)
+{
+	OSMO_ASSERT(pp->ref_count == 0);
+	llist_del(&pp->entry);
+	talloc_free(pp);
+}
+
+/* From the information in the gtp_packet_desc, return the address of a GGSN.
+ * Return -1 on error. */
+static struct gtphub_peer_port *gtphub_resolve_ggsn(struct gtphub *hub,
+						    struct gtp_packet_desc *p);
+
+/* See gtphub_ext.c (wrapped by unit test) */
+int gtphub_resolve_ggsn_addr(struct gtphub *hub,
+			     struct osmo_sockaddr *result,
+			     struct gtp_packet_desc *p);
+
+static struct gtphub_peer_port *gtphub_port_find(const struct gtphub_bind *bind,
+						 const struct gsn_addr *addr,
+						 uint16_t port);
+
+static struct gtphub_peer_port *gtphub_port_have(struct gtphub *hub,
+						 struct gtphub_bind *bind,
+						 const struct gsn_addr *addr,
+						 uint16_t port);
+
+static void gtphub_zero(struct gtphub *hub)
+{
+	ZERO_STRUCT(hub);
+}
+
+static int gtphub_sock_init(struct osmo_fd *ofd,
+			    const struct gtphub_cfg_addr *addr,
+			    osmo_fd_cb_t cb,
+			    void *data,
+			    int ofd_id)
+{
+	if (!addr->addr_str) {
+		LOGERR("Cannot bind: empty address.\n");
+		return -1;
+	}
+	if (!addr->port) {
+		LOGERR("Cannot bind: zero port not permitted.\n");
+		return -1;
+	}
+
+	ofd->when = BSC_FD_READ;
+	ofd->cb = cb;
+	ofd->data = data;
+	ofd->priv_nr = ofd_id;
+
+	int rc;
+	rc = osmo_sock_init_ofd(ofd,
+				AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				addr->addr_str, addr->port,
+				OSMO_SOCK_F_BIND);
+	if (rc < 1) {
+		LOGERR("Cannot bind to %s port %d (rc %d)\n",
+		       addr->addr_str, (int)addr->port, rc);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void gtphub_bind_init(struct gtphub_bind *b)
+{
+	ZERO_STRUCT(b);
+
+	INIT_LLIST_HEAD(&b->peers);
+}
+
+static int gtphub_bind_start(struct gtphub_bind *b,
+			     const struct gtphub_cfg_bind *cfg,
+			     osmo_fd_cb_t cb, void *cb_data,
+			     unsigned int ofd_id)
+{
+	if (gsn_addr_from_str(&b->local_addr, cfg->bind.addr_str) != 0)
+		return -1;
+	if (gtphub_sock_init(&b->ofd, &cfg->bind, cb, cb_data, ofd_id) != 0)
+		return -1;
+	return 0;
+}
+
+/* Recv datagram from from->fd, optionally write sender's address to *from_addr.
+ * Return the number of bytes read, zero on error. */
+static int gtphub_read(const struct osmo_fd *from,
+		       struct osmo_sockaddr *from_addr,
+		       uint8_t *buf, size_t buf_len)
+{
+	/* recvfrom requires the available length to be set in *from_addr_len. */
+	if (from_addr)
+		from_addr->l = sizeof(from_addr->a);
+
+	errno = 0;
+	ssize_t received = recvfrom(from->fd, buf, buf_len, 0,
+				    (struct sockaddr*)&from_addr->a, &from_addr->l);
+	/* TODO use recvmsg and get a MSG_TRUNC flag to make sure the message
+	 * is not truncated. Then maybe reduce buf's size. */
+
+	if (received <= 0) {
+		if (errno != EAGAIN)
+			LOGERR("error: %s\n", strerror(errno));
+		return 0;
+	}
+
+	if (from_addr) {
+		LOG("from %s\n", osmo_sockaddr_to_str(from_addr));
+	}
+
+	if (received <= 0) {
+		LOGERR("error: %s\n", strerror(errno));
+		return 0;
+	}
+
+	LOG("Received %d\n%s\n", (int)received, osmo_hexdump(buf, received));
+	return received;
+}
+
+inline void gtphub_port_ref_count_inc(struct gtphub_peer_port *pp)
+{
+	OSMO_ASSERT(pp->ref_count < UINT_MAX);
+	pp->ref_count++;
+}
+
+inline void gtphub_port_ref_count_dec(struct gtphub_peer_port *pp)
+{
+	OSMO_ASSERT(pp->ref_count > 0);
+	pp->ref_count--;
+}
+
+inline void set_seq(struct gtp_packet_desc *p, uint16_t seq)
+{
+	OSMO_ASSERT(p->version == 1);
+	p->data->gtp1l.h.seq = hton16(seq);
+	p->seq = seq;
+}
+
+inline void set_tei(struct gtp_packet_desc *p, uint32_t tei)
+{
+	OSMO_ASSERT(p->version == 1);
+	p->data->gtp1l.h.tei = hton32(tei);
+	p->header_tei = tei;
+}
+
+static void gtphub_mapping_del_cb(struct expiring_item *expi);
+
+static struct nr_mapping *gtphub_mapping_new()
+{
+	struct nr_mapping *nrm;
+	nrm = talloc_zero(osmo_gtphub_ctx, struct nr_mapping);
+	OSMO_ASSERT(nrm);
+
+	nr_mapping_init(nrm);
+	nrm->expiry_entry.del_cb = gtphub_mapping_del_cb;
+	return nrm;
+}
+
+static const char *gtphub_peer_strb(struct gtphub_peer *peer, char *buf, int buflen)
+{
+	if (llist_empty(&peer->addresses))
+		return "(addressless)";
+
+	struct gtphub_peer_addr *a = llist_first(&peer->addresses,
+						 struct gtphub_peer_addr,
+						 entry);
+	return gsn_addr_to_strb(&a->addr, buf, buflen);
+}
+
+static const char *gtphub_port_strb(struct gtphub_peer_port *port, char *buf, int buflen)
+{
+	if (!port)
+		return "(null port)";
+
+	snprintf(buf, buflen, "%s port %d",
+		 gsn_addr_to_str(&port->peer_addr->addr),
+		 (int)port->port);
+	return buf;
+}
+
+const char *gtphub_peer_str(struct gtphub_peer *peer)
+{
+	static char buf[256];
+	return gtphub_peer_strb(peer, buf, sizeof(buf));
+}
+
+const char *gtphub_peer_str2(struct gtphub_peer *peer)
+{
+	static char buf[256];
+	return gtphub_peer_strb(peer, buf, sizeof(buf));
+}
+
+static const char *gtphub_port_str(struct gtphub_peer_port *port)
+{
+	static char buf[256];
+	return gtphub_port_strb(port, buf, sizeof(buf));
+}
+
+static const char *gtphub_port_str2(struct gtphub_peer_port *port)
+{
+	static char buf[256];
+	return gtphub_port_strb(port, buf, sizeof(buf));
+}
+
+static void gtphub_mapping_del_cb(struct expiring_item *expi)
+{
+	expi->del_cb = 0; /* avoid recursion loops */
+
+	struct nr_mapping *nrm = container_of(expi,
+					      struct nr_mapping,
+					      expiry_entry);
+	llist_del(&nrm->entry);
+	INIT_LLIST_HEAD(&nrm->entry); /* mark unused */
+
+	/* Just for log */
+	struct gtphub_peer_port *from = nrm->origin;
+	OSMO_ASSERT(from);
+	LOG("expired: %d: nr mapping from %s: %d->%d\n",
+	    (int)nrm->expiry_entry.expiry,
+	    gtphub_port_str(from),
+	    (int)nrm->orig, (int)nrm->repl);
+
+	gtphub_port_ref_count_dec(from);
+
+	talloc_free(nrm);
+}
+
+static struct nr_mapping *gtphub_mapping_have(struct nr_map *map,
+					      struct gtphub_peer_port *from,
+					      nr_t orig_nr,
+					      time_t now)
+{
+	struct nr_mapping *nrm;
+
+	nrm = nr_map_get(map, from, orig_nr);
+
+	if (!nrm) {
+		nrm = gtphub_mapping_new();
+		nrm->orig = orig_nr;
+		nrm->origin = from;
+		nr_map_add(map, nrm, now);
+		gtphub_port_ref_count_inc(from);
+		LOG("peer %s: MAP %d --> %d\n",
+		    gtphub_port_str(from),
+		    (int)(nrm->orig), (int)(nrm->repl));
+	} else {
+		/* restart expiry timeout */
+		expiry_add(map->add_items_to_expiry, &nrm->expiry_entry,
+			   now);
+	}
+
+	OSMO_ASSERT(nrm);
+	return nrm;
+}
+
+static uint32_t gtphub_tei_mapping_have(struct gtphub *hub,
+					int plane_idx,
+					struct gtphub_peer_port *from,
+					uint32_t orig_tei,
+					time_t now)
+{
+	struct nr_mapping *nrm = gtphub_mapping_have(&hub->tei_map[plane_idx],
+						     from, orig_tei, now);
+	LOG("New %s TEI: (from %s, TEI %d) <-- TEI %d\n",
+	    gtphub_plane_idx_names[plane_idx],
+	    gtphub_port_str(from),
+	    (int)orig_tei, (int)nrm->repl);
+
+	return (uint32_t)nrm->repl;
+}
+
+static int gtphub_map_seq(struct gtp_packet_desc *p,
+			  struct gtphub_peer_port *from_port,
+			  struct gtphub_peer_port *to_port,
+			  time_t now)
+{
+	/* Store a mapping in to_peer's map, so when we later receive a GTP
+	 * packet back from to_peer, the seq nr can be unmapped back to its
+	 * origin (from_peer here). */
+	struct nr_mapping *nrm;
+	nrm = gtphub_mapping_have(&to_port->peer_addr->peer->seq_map,
+				  from_port, p->seq, now);
+
+	/* Change the GTP packet to yield the new, mapped seq nr */
+	set_seq(p, nrm->repl);
+
+	return 0;
+}
+
+static struct gtphub_peer_port *gtphub_unmap_seq(struct gtp_packet_desc *p,
+						 struct gtphub_peer_port *responding_port)
+{
+	OSMO_ASSERT(p->version == 1);
+	struct nr_mapping *nrm = nr_map_get_inv(&responding_port->peer_addr->peer->seq_map,
+						p->seq);
+	if (!nrm)
+		return NULL;
+	LOG("peer %p: UNMAP %d <-- %d\n", nrm->origin, (int)(nrm->orig), (int)(nrm->repl));
+	set_seq(p, nrm->orig);
+	return nrm->origin;
+}
+
+static void gtphub_check_restart_counter(struct gtphub *hub,
+					 struct gtp_packet_desc *p,
+					 struct gtphub_peer_port *from)
+{
+	/* TODO */
+	/* If the peer is sending a Recovery IE (7.7.11) with a restart counter
+	 * that doesn't match the peer's previously sent restart counter, clear
+	 * that peer and cancel PDP contexts. */
+}
+
+static void gtphub_map_restart_counter(struct gtphub *hub,
+				       struct gtp_packet_desc *p,
+				       struct gtphub_peer_port *from,
+				       struct gtphub_peer_port *to)
+{
+	/* TODO */
+}
+
+/* gtphub_map_ie_teis() and gtphub_unmap_header_tei():
+ *
+ * TEI mapping must happen symmetrically. An SGSN contacts gtphub instead of N
+ * GGSNs, and a GGSN replies to gtphub for N SGSNs. From either end, TEIs may
+ * collide: two GGSNs picking the same TEIs, or two SGSNs picking the same
+ * TEIs. Since the opposite side sees the sender address being gtphub's
+ * address, TEIs among the SGSNs, and among the GGSNs, must not overlap. If a
+ * peer sends a TEI already sent before from a peer of the same side, gtphub
+ * replaces it with a TEI not yet seen from that side and remembers the
+ * mapping.
+ *
+ * Consider two SGSNs A and B contacting two GGSNs C and D thru gtphub.
+ *
+ * A: Create PDP Ctx, I have TEI 1.
+ *    --->   gtphub: A has TEI 1, sending 1 for C.
+ *              --->   C: gtphub has TEI 1.
+ *      	<---   C: Response to TEI 1: I have TEI 11.
+ *    <---   gtphub: ok, telling A: 11.
+ * A: gtphub's first TEI is 11.                                         (1)
+ *
+ * B: Create PDP Ctx, I have TEIs 1.
+ *    --->   gtphub: 1 already taken for C, sending 2 for B. (map)
+ *              --->   C: gtphub also has 2.
+ *      	<---   C: Response to TEI 2: I have TEI 12.
+ *    <---   gtphub: ok, TEI 2 is actually B with TEI 1. (unmap)
+ * B: gtphub's first TEI is 12, as far as I can tell.
+ *
+ * Now the second GGSN comes into play:
+ *
+ * A: Create PDP Ctx, I have TEI 2.
+ *    --->   gtphub: A also has TEI 2, but for D, sending 1.            (2)
+ *              --->   D: gtphub has 1.
+ *      	<---   D: Response to TEI 1: I have TEI 11.
+ *    <---   gtphub: from D, 1 is A. 11 already taken by C, sending 13. (3)
+ * A: gtphub also has TEI 13.                                           (4)
+ *
+ * And some messages routed through:
+ *
+ * A: message to TEI 11, see (1).
+ *    --->   gtphub: ok, telling C with TEI 11.
+ *              --->   C: I see, 11 means reply with 1.
+ *      	<---   C: Response to TEI 1
+ *    <---   gtphub: 1 from C is actually for A with TEI 1.
+ * A: ah, my TEI 1, thanks!
+ *
+ * A: message to TEI 13, see (4).
+ *    --->   gtphub: ok, but not 13, D wanted TEI 11 instead, see (3).
+ *              --->   D: I see, 11 means reply with 1.
+ *      	<---   D: Response to TEI 1
+ *    <---   gtphub: 1 from D is actually for A with TEI 2, see (2).
+ * A: ah, my TEI 2, thanks!
+ *
+ * What if a GGSN initiates a request:
+ *
+ *              <---   D: Request to gtphub TEI 1
+ *    <---   gtphub: 1 from D is for A with 2, see (2).
+ * A: my TEI 2 means reply with 13.
+ *    --->   gtphub: 13 was D with 11, see (3).
+ *              --->   D: 11 from gtphub: a reply to my request for TEI 1.
+ *
+ * Note that usually, it's the sequence numbers that route a response back to
+ * the requesting peer. Nevertheless, the TEI mappings must be carried out to
+ * replace the TEIs in the GTP packet that is relayed.
+ *
+ * Also note: the TEI in the GTP header is "reversed" from the TEI in the IEs:
+ * the TEI in the header is used to send something *to* a peer, while the TEI
+ * in e.g. a Create PDP Context Request's IE is for routing messages *back*
+ * later. */
+
+static int gtphub_unmap_header_tei(struct gtphub_peer_port **to_port_p,
+				   struct gtphub *hub,
+				   struct gtp_packet_desc *p,
+				   struct gtphub_peer_port *from_port)
+{
+	OSMO_ASSERT(p->version == 1);
+	*to_port_p = NULL;
+
+	/* If the header's TEI is zero, no PDP context has been established
+	 * yet. If nonzero, a mapping should actually already exist for this
+	 * TEI, since it must have been announced in a PDP context creation. */
+	uint32_t tei = p->header_tei;
+	if (!tei)
+		return 0;
+
+	/* to_peer has previously announced a TEI, which was stored and
+	 * mapped in from_peer's tei_map. */
+	struct nr_mapping *nrm;
+	nrm = nr_map_get_inv(&hub->tei_map[p->plane_idx], tei);
+	if (!nrm) {
+		LOGERR("Received unknown TEI %" PRIu32 " from %s\n",
+		       tei, gtphub_port_str(from_port));
+		return -1;
+	}
+
+	struct gtphub_peer_port *to_port = nrm->origin;
+	uint32_t unmapped_tei = nrm->orig;
+	set_tei(p, unmapped_tei);
+
+	LOG("Unmapped TEI coming from %s: %d -> %d (to %s)\n",
+	    gtphub_port_str(from_port), tei, unmapped_tei,
+	    gtphub_port_str2(to_port));
+
+	*to_port_p = to_port;
+	return 0;
+}
+
+/* Read GSN address IEs from p, and make sure these peer addresses exist in
+ * bind[plane_idx] with default ports, in their respective planes (both Ctrl
+ * and User). Map TEIs announced in IEs, and write mapped TEIs in-place into
+ * the packet p. */
+static int gtphub_handle_pdp_ctx_ies(struct gtphub *hub,
+				     struct gtphub_bind from_bind[],
+				     struct gtphub_bind to_bind[],
+				     struct gtp_packet_desc *p,
+				     time_t now)
+{
+	OSMO_ASSERT(p->plane_idx == GTPH_PLANE_CTRL);
+
+	int rc;
+	int plane_idx;
+
+	switch (p->type) {
+	case GTP_CREATE_PDP_REQ:
+	case GTP_CREATE_PDP_RSP:
+		/* Go for it below */
+		break;
+	default:
+		/* Nothing to do for this message type. */
+		return 0;
+	}
+
+	/* TODO enforce a Request only from SGSN, a Response only from GGSN? */
+
+	osmo_static_assert((GTPH_PLANE_CTRL == 0) && (GTPH_PLANE_USER == 1),
+			   plane_nrs_match_GSN_addr_IE_indices);
+
+	uint8_t ie_type[] = { GTPIE_TEI_C, GTPIE_TEI_DI };
+	int ie_mandatory = (p->type == GTP_CREATE_PDP_REQ);
+
+	for (plane_idx = 0; plane_idx < 2; plane_idx++) {
+		struct gsn_addr addr_from_ie;
+		uint32_t tei_from_ie;
+		int ie_idx;
+
+		/* Fetch GSN Address and TEI from IEs */
+		rc = gsn_addr_get(&addr_from_ie, p, plane_idx);
+		if (rc) {
+			LOGERR("Cannot read %s GSN Address IE\n",
+			       gtphub_plane_idx_names[plane_idx]);
+			return -1;
+		}
+		LOG("Read %s GSN addr %s (%d)\n",
+		    gtphub_plane_idx_names[plane_idx],
+		    gsn_addr_to_str(&addr_from_ie),
+		    addr_from_ie.len);
+
+		ie_idx = gtpie_getie(p->ie, ie_type[plane_idx], 0);
+		if (ie_idx < 0) {
+			if (ie_mandatory) {
+				LOGERR("Create PDP Context message invalid:"
+				       " missing IE %d\n", (int)ie_type[plane_idx]);
+				return -1;
+			}
+			tei_from_ie = 0;
+		}
+		else
+			tei_from_ie = ntoh32(p->ie[ie_idx]->tv4.v);
+
+		/* Make sure an entry for this peer address with default port
+		 * exists */
+		struct gtphub_peer_port *peer_from_ie =
+			gtphub_port_have(hub, &from_bind[plane_idx],
+					 &addr_from_ie,
+					 gtphub_plane_idx_default_port[plane_idx]);
+
+		if (tei_from_ie) {
+			/* Create TEI mapping and replace in GTP packet IE */
+			uint32_t mapped_tei =
+				gtphub_tei_mapping_have(hub, plane_idx,
+							peer_from_ie,
+							tei_from_ie,
+							now);
+			p->ie[ie_idx]->tv4.v = hton32(mapped_tei);
+		}
+
+		/* Replace the GSN address to reflect gtphub. */
+		rc = gsn_addr_put(&to_bind[plane_idx].local_addr, p, plane_idx);
+		if (rc) {
+			LOGERR("Cannot write %s GSN Address IE\n",
+			       gtphub_plane_idx_names[plane_idx]);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+static int gtphub_write(const struct osmo_fd *to,
+			const struct osmo_sockaddr *to_addr,
+			const uint8_t *buf, size_t buf_len)
+{
+	errno = 0;
+	ssize_t sent = sendto(to->fd, buf, buf_len, 0,
+			      (struct sockaddr*)&to_addr->a, to_addr->l);
+
+	if (to_addr) {
+		LOG("to %s\n", osmo_sockaddr_to_str(to_addr));
+	}
+
+	if (sent == -1) {
+		LOGERR("error: %s\n", strerror(errno));
+		return -EINVAL;
+	}
+
+	if (sent != buf_len)
+		LOGERR("sent(%d) != data_len(%d)\n", (int)sent, (int)buf_len);
+	else
+		LOG("Sent %d\n%s\n", (int)sent, osmo_hexdump(buf, sent));
+
+	return 0;
+}
+
+static int from_ggsns_read_cb(struct osmo_fd *from_ggsns_ofd, unsigned int what)
+{
+	unsigned int plane_idx = from_ggsns_ofd->priv_nr;
+	OSMO_ASSERT(plane_idx < GTPH_PLANE_N);
+	LOG("\n\n=== reading from GGSN (%s)\n", gtphub_plane_idx_names[plane_idx]);
+	if (!(what & BSC_FD_READ))
+		return 0;
+
+	struct gtphub *hub = from_ggsns_ofd->data;
+
+	static uint8_t buf[4096];
+	struct osmo_sockaddr from_addr;
+	struct osmo_sockaddr to_addr;
+	struct osmo_fd *to_ofd;
+	size_t len;
+
+	len = gtphub_read(from_ggsns_ofd, &from_addr, buf, sizeof(buf));
+	if (len < 1)
+		return 0;
+
+	len = gtphub_from_ggsns_handle_buf(hub, plane_idx, &from_addr, buf, len,
+					   gtphub_now(),
+					   &to_ofd, &to_addr);
+	if (len < 1)
+		return 0;
+
+	return gtphub_write(to_ofd, &to_addr, buf, len);
+}
+
+static int gtphub_unmap(struct gtphub *hub,
+			struct gtp_packet_desc *p,
+			struct gtphub_peer_port *from,
+			struct gtphub_peer_port *to_proxy,
+			struct gtphub_peer_port **final_unmapped,
+			struct gtphub_peer_port **unmapped_from_seq,
+			struct gtphub_peer_port **unmapped_from_tei)
+{
+	/* Always (try to) unmap sequence and TEI numbers, which need to be
+	 * replaced in the packet. Either way, give precedence to the proxy, if
+	 * configured. */
+
+	struct gtphub_peer_port *from_seq = NULL;
+	struct gtphub_peer_port *from_tei = NULL;
+	struct gtphub_peer_port *unmapped = NULL;
+
+	if (unmapped_from_seq)
+		*unmapped_from_seq = from_seq;
+	if (unmapped_from_tei)
+		*unmapped_from_tei = from_tei;
+	if (final_unmapped)
+		*final_unmapped = unmapped;
+
+	from_seq = gtphub_unmap_seq(p, from);
+
+	if (gtphub_unmap_header_tei(&from_tei, hub, p, from) < 0)
+		return -1;
+
+	struct gtphub_peer *from_peer = from->peer_addr->peer;
+	if (from_seq && from_tei && (from_seq != from_tei)) {
+		LOGERR("Seq unmap and TEI unmap yield two different peers. Using seq unmap."
+		       "(from %s %s: seq %d yields %s, tei %u yields %s)\n",
+		       gtphub_plane_idx_names[p->plane_idx],
+		       gtphub_peer_str(from_peer),
+		       (int)p->seq,
+		       gtphub_port_str(from_seq),
+		       (int)p->header_tei,
+		       gtphub_port_str2(from_tei)
+		       );
+	}
+	unmapped = (from_seq? from_seq : from_tei);
+
+	if (unmapped && to_proxy && (unmapped != to_proxy)) {
+		LOGERR("Unmap yields a different peer than the configured proxy. Using proxy."
+		       " unmapped: %s  proxy: %s\n",
+		       gtphub_port_str(unmapped),
+		       gtphub_port_str2(to_proxy)
+		       );
+	}
+	unmapped = (to_proxy? to_proxy : unmapped);
+
+	if (!unmapped) {
+		/* Return no error, but returned pointers are all NULL. */
+		return 0;
+	}
+
+	LOG("from seq %p; from tei %p; unmapped => %p\n",
+	    from_seq, from_tei, unmapped);
+
+	if (unmapped_from_seq)
+		*unmapped_from_seq = from_seq;
+	if (unmapped_from_tei)
+		*unmapped_from_tei = from_tei;
+	if (final_unmapped)
+		*final_unmapped = unmapped;
+	return 0;
+}
+
+static int gsn_addr_to_sockaddr(struct gsn_addr *src,
+				uint16_t port,
+				struct osmo_sockaddr *dst)
+{
+	return osmo_sockaddr_init_udp(dst, gsn_addr_to_str(src), port);
+}
+
+static int gtphub_handle_echo(const struct gtp_packet_desc *p)
+{
+	/* TODO */
+	return 0;
+}
+
+/* Parse buffer as GTP packet, replace elements in-place and return the ofd and
+ * address to forward to. Return a pointer to the osmo_fd, but copy the
+ * sockaddr to *to_addr. The reason for this is that the sockaddr may expire at
+ * any moment, while the osmo_fd is guaranteed to persist. Return the number of
+ * bytes to forward, 0 or less on failure. */
+int gtphub_from_ggsns_handle_buf(struct gtphub *hub,
+				 unsigned int plane_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 time_t now,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr *to_addr)
+{
+	LOG("<- rx from GGSN %s\n", osmo_sockaddr_to_str(from_addr));
+
+	*to_ofd = &hub->to_sgsns[plane_idx].ofd;
+
+	static struct gtp_packet_desc p;
+	gtp_decode(buf, received, plane_idx, &p);
+
+	if (p.rc <= 0)
+		return -1;
+
+	int rc;
+	rc = gtphub_handle_echo(&p);
+	if (rc == 1) {
+		/* It was en echo. Nothing left to do. */
+		/* (*to_ofd already set above.) */
+		osmo_sockaddr_copy(to_addr, from_addr);
+		return 0;
+	}
+	if (rc < 0)
+		return -1; /* Invalid packet. */
+
+	/* If a GGSN proxy is configured, check that it's indeed that proxy
+	 * talking to us. A proxy is a forced 1:1 connection, e.g. to another
+	 * gtphub, so no-one else is allowed to talk to us from that side. */
+	struct gtphub_peer_port *ggsn = hub->ggsn_proxy[plane_idx];
+	if (ggsn) {
+		if (osmo_sockaddr_cmp(&ggsn->sa, from_addr) != 0) {
+			LOGERR("Rejecting: GGSN proxy configured, but GTP packet"
+			       " received on GGSN bind is from another sender:"
+			       " proxy: %s  sender: %s\n",
+			       gtphub_port_str(ggsn),
+			       osmo_sockaddr_to_str(from_addr));
+			return -1;
+		}
+	}
+
+	if (!ggsn) {
+		ggsn = gtphub_port_find_sa(&hub->to_ggsns[plane_idx], from_addr);
+	}
+
+	/* If any PDP context has been created, we already have an entry for
+	 * this GGSN. If we don't have an entry, the GGSN has nothing to tell
+	 * us about. */
+	if (!ggsn) {
+		LOGERR("Invalid GGSN peer. Dropping packet.\n");
+		return -1;
+	}
+
+	LOG("GGSN peer: %s\n", gtphub_port_str(ggsn));
+
+	struct gtphub_peer_port *sgsn_from_seq;
+	struct gtphub_peer_port *sgsn;
+	if (gtphub_unmap(hub, &p, ggsn,
+			 hub->sgsn_proxy[plane_idx],
+			 &sgsn, &sgsn_from_seq,
+			 NULL /* not interested, got it in &sgsn already */
+			)
+	    != 0) {
+		return -1;
+	}
+
+	if (!sgsn) {
+		/* A GGSN initiated request would go to a known TEI. So this is
+		 * bogus. */
+		LOGERR("No SGSN to send to. Dropping packet.\n");
+		return -1;
+	}
+
+	if (plane_idx == GTPH_PLANE_CTRL) {
+		/* This may be a Create PDP Context response. If it is, there are other
+		 * addresses in the GTP message to set up apart from the sender. */
+		if (gtphub_handle_pdp_ctx_ies(hub, hub->to_ggsns,
+					      hub->to_sgsns, &p, now)
+		    != 0)
+			return -1;
+	}
+
+	gtphub_check_restart_counter(hub, &p, ggsn);
+	gtphub_map_restart_counter(hub, &p, ggsn, sgsn);
+
+	/* If the GGSN is replying to an SGSN request, the sequence nr has
+	 * already been unmapped above (sgsn_from_seq != NULL), and we need not
+	 * create a new mapping. */
+	if (!sgsn_from_seq)
+		gtphub_map_seq(&p, ggsn, sgsn, now);
+
+	osmo_sockaddr_copy(to_addr, &sgsn->sa);
+	return received;
+}
+
+static int from_sgsns_read_cb(struct osmo_fd *from_sgsns_ofd, unsigned int what)
+{
+	unsigned int plane_idx = from_sgsns_ofd->priv_nr;
+	OSMO_ASSERT(plane_idx < GTPH_PLANE_N);
+	LOG("\n\n=== reading from SGSN (%s)\n", gtphub_plane_idx_names[plane_idx]);
+
+	if (!(what & BSC_FD_READ))
+		return 0;
+
+	struct gtphub *hub = from_sgsns_ofd->data;
+
+	static uint8_t buf[4096];
+	struct osmo_sockaddr from_addr;
+	struct osmo_sockaddr to_addr;
+	struct osmo_fd *to_ofd;
+	size_t len;
+
+	len = gtphub_read(from_sgsns_ofd, &from_addr, buf, sizeof(buf));
+	if (len < 1)
+		return 0;
+
+	len = gtphub_from_sgsns_handle_buf(hub, plane_idx, &from_addr, buf, len,
+					   gtphub_now(),
+					   &to_ofd, &to_addr);
+	if (len < 1)
+		return 0;
+
+	return gtphub_write(to_ofd, &to_addr, buf, len);
+}
+
+/* Analogous to gtphub_from_ggsns_handle_buf(), see the comment there. */
+int gtphub_from_sgsns_handle_buf(struct gtphub *hub,
+				 unsigned int plane_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 time_t now,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr *to_addr)
+{
+	LOG("-> rx from SGSN %s\n", osmo_sockaddr_to_str(from_addr));
+
+	*to_ofd = &hub->to_ggsns[plane_idx].ofd;
+
+	static struct gtp_packet_desc p;
+	gtp_decode(buf, received, plane_idx, &p);
+
+	if (p.rc <= 0)
+		return -1;
+
+	int rc;
+	rc = gtphub_handle_echo(&p);
+	if (rc == 1) {
+		/* It was en echo. Nothing left to do. */
+		/* (*to_ofd already set above.) */
+		osmo_sockaddr_copy(to_addr, from_addr);
+		return 0;
+	}
+	if (rc < 0)
+		return -1; /* Invalid packet. */
+
+	/* If an SGSN proxy is configured, check that it's indeed that proxy
+	 * talking to us. A proxy is a forced 1:1 connection, e.g. to another
+	 * gtphub, so no-one else is allowed to talk to us from that side. */
+	struct gtphub_peer_port *sgsn = hub->sgsn_proxy[plane_idx];
+	if (sgsn) {
+		if (osmo_sockaddr_cmp(&sgsn->sa, from_addr) != 0) {
+			LOGERR("Rejecting: GGSN proxy configured, but GTP packet"
+			       " received on GGSN bind is from another sender:"
+			       " proxy: %s  sender: %s\n",
+			       gtphub_port_str(sgsn),
+			       osmo_sockaddr_to_str(from_addr));
+			return -1;
+		}
+	}
+
+	if (!sgsn) {
+		/* If any contact has been made before, we already have an
+		 * entry for this SGSN. */
+		sgsn = gtphub_port_find_sa(&hub->to_sgsns[plane_idx], from_addr);
+	}
+
+	if (!sgsn) {
+		/* A new peer. If this is on the Ctrl plane, an SGSN may make
+		 * first contact without being known yet, so create the peer
+		 * struct for the current sender. */
+		if (plane_idx != GTPH_PLANE_CTRL) {
+			LOGERR("User plane peer was not announced by PDP Context, discarding: %s\n",
+			       osmo_sockaddr_to_str(from_addr));
+			return -1;
+		}
+
+		struct gsn_addr from_gsna;
+		uint16_t from_port;
+		if (gsn_addr_from_sockaddr(&from_gsna, &from_port, from_addr) != 0)
+			return -1;
+
+		sgsn = gtphub_port_have(hub, &hub->to_sgsns[plane_idx],
+					&from_gsna, from_port);
+	}
+
+	if (!sgsn) {
+		/* This could theoretically happen for invalid address data or somesuch. */
+		LOGERR("Invalid SGSN peer. Dropping packet.\n");
+		return -1;
+	}
+	LOG("SGSN peer: %s\n", gtphub_port_str(sgsn));
+
+	struct gtphub_peer_port *ggsn_from_seq;
+	struct gtphub_peer_port *ggsn;
+	if (gtphub_unmap(hub, &p, sgsn,
+			 hub->ggsn_proxy[plane_idx],
+			 &ggsn, &ggsn_from_seq,
+			 NULL /* not interested, got it in &ggsn already */
+			)
+	    != 0) {
+		return -1;
+	}
+
+	/* See what our GGSN guess would be from the packet data per se. */
+	/* TODO maybe not do this always? */
+	struct gtphub_peer_port *ggsn_from_packet;
+	ggsn_from_packet = gtphub_resolve_ggsn(hub, &p);
+
+	if (ggsn_from_packet && ggsn
+	    && (ggsn_from_packet != ggsn)) {
+		LOGERR("GGSN implied from packet does not match unmapped"
+		       " GGSN, using unmapped GGSN:"
+		       " from packet: %s  unmapped: %s\n",
+		       gtphub_port_str(ggsn_from_packet),
+		       gtphub_port_str2(ggsn));
+		/* TODO return -1; ? */
+	}
+
+	if (!ggsn)
+		ggsn = ggsn_from_packet;
+
+	if (!ggsn) {
+		LOGERR("No GGSN to send to. Dropping packet.\n");
+		return -1;
+	}
+
+	if (plane_idx == GTPH_PLANE_CTRL) {
+		/* This may be a Create PDP Context requst. If it is, there are other
+		 * addresses in the GTP message to set up apart from the sender. */
+		if (gtphub_handle_pdp_ctx_ies(hub, hub->to_sgsns,
+					      hub->to_ggsns, &p, now)
+		    != 0)
+			return -1;
+	}
+
+	gtphub_check_restart_counter(hub, &p, sgsn);
+	gtphub_map_restart_counter(hub, &p, sgsn, ggsn);
+
+	/* If the SGSN is replying to a GGSN request, the sequence nr has
+	 * already been unmapped above (unmap_ggsn != NULL), and we need not
+	 * create a new outgoing sequence map. */
+	if (!ggsn_from_seq)
+		gtphub_map_seq(&p, sgsn, ggsn, now);
+
+	osmo_sockaddr_copy(to_addr, &ggsn->sa);
+
+	return received;
+}
+
+static int gtphub_gc_peer_port(struct gtphub_peer_port *pp)
+{
+	return pp->ref_count == 0;
+}
+
+static int gtphub_gc_peer_addr(struct gtphub_peer_addr *pa)
+{
+	struct gtphub_peer_port *pp, *npp;
+	llist_for_each_entry_safe(pp, npp, &pa->ports, entry) {
+		if (gtphub_gc_peer_port(pp)) {
+			LOG("expired: peer %s\n",
+			    gtphub_port_str(pp));
+			gtphub_peer_port_del(pp);
+		}
+	}
+	return llist_empty(&pa->ports);
+}
+
+static int gtphub_gc_peer(struct gtphub_peer *p)
+{
+	struct gtphub_peer_addr *pa, *npa;
+	llist_for_each_entry_safe(pa, npa, &p->addresses, entry) {
+		if (gtphub_gc_peer_addr(pa)) {
+			gtphub_peer_addr_del(pa);
+		}
+	}
+
+	/* Note that there's a ref_count in each gtphub_peer_port instance
+	 * listed within p->addresses, referenced by TEI mappings from
+	 * hub->tei_map. As long as those don't expire, this peer will stay. */
+
+	LOG("gc peer %p llist_empty %d  seq_map_empty %d\n", p,
+	(int)llist_empty(&p->addresses), (int) nr_map_empty(&p->seq_map));
+	if (! nr_map_empty(&p->seq_map)) {
+		printf("not empty\n");
+		struct nr_mapping *nrm;
+		llist_for_each_entry(nrm, &p->seq_map.mappings, entry) {
+			printf("%p %s %d -> %d\n",
+			       nrm->origin, gtphub_port_str(nrm->origin),nrm->orig, nrm->repl);
+		}
+	}
+	return llist_empty(&p->addresses)
+		&& nr_map_empty(&p->seq_map);
+}
+
+static void gtphub_gc_bind(struct gtphub_bind *b)
+{
+	struct gtphub_peer *p, *n;
+	llist_for_each_entry_safe(p, n, &b->peers, entry) {
+		if (gtphub_gc_peer(p)) {
+			gtphub_peer_del(p);
+		}
+	}
+}
+
+void gtphub_gc(struct gtphub *hub, time_t now)
+{
+	int expired;
+	expired = expiry_tick(&hub->expire_seq_maps, now);
+	expired += expiry_tick(&hub->expire_tei_maps, now);
+
+	/* ... */
+
+	if (expired) {
+		int i;
+		for (i = 0; i < GTPH_PLANE_N; i++) {
+			gtphub_gc_bind(&hub->to_sgsns[i]);
+			gtphub_gc_bind(&hub->to_ggsns[i]);
+		}
+	}
+}
+
+static void gtphub_gc_cb(void *data)
+{
+	struct gtphub *hub = data;
+	gtphub_gc(hub, gtphub_now());
+	osmo_timer_schedule(&hub->gc_timer, GTPH_GC_TICK_SECONDS, 0);
+}
+
+static void gtphub_gc_start(struct gtphub *hub)
+{
+	hub->gc_timer.cb = gtphub_gc_cb;
+	hub->gc_timer.data = hub;
+
+	osmo_timer_schedule(&hub->gc_timer, GTPH_GC_TICK_SECONDS, 0);
+}
+
+/* called by unit tests */
+void gtphub_init(struct gtphub *hub)
+{
+	gtphub_zero(hub);
+
+	expiry_init(&hub->expire_seq_maps, GTPH_SEQ_MAPPING_EXPIRY_SECS);
+	expiry_init(&hub->expire_tei_maps, GTPH_TEI_MAPPING_EXPIRY_MINUTES * 60);
+
+	int plane_idx;
+	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
+		nr_pool_init(&hub->tei_pool[plane_idx]);
+		nr_map_init(&hub->tei_map[plane_idx],
+			    &hub->tei_pool[plane_idx],
+			    &hub->expire_tei_maps);
+
+		gtphub_bind_init(&hub->to_ggsns[plane_idx]);
+		gtphub_bind_init(&hub->to_sgsns[plane_idx]);
+	}
+}
+
+static int gtphub_make_proxy(struct gtphub *hub,
+			     struct gtphub_peer_port **pp,
+			     struct gtphub_bind *bind,
+			     const struct gtphub_cfg_addr *addr)
+{
+	if (!addr->addr_str)
+		return 0;
+
+	struct gsn_addr gsna;
+	if (gsn_addr_from_str(&gsna, addr->addr_str) != 0)
+		return -1;
+
+	*pp = gtphub_port_have(hub, bind, &gsna, addr->port);
+
+	/* This is *the* proxy. Make sure it is never expired. */
+	gtphub_port_ref_count_inc(*pp);
+	return 0;
+}
+
+int gtphub_start(struct gtphub *hub, struct gtphub_cfg *cfg)
+{
+	int rc;
+
+	gtphub_init(hub);
+
+	int plane_idx;
+	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
+		rc = gtphub_bind_start(&hub->to_ggsns[plane_idx],
+				       &cfg->to_ggsns[plane_idx],
+				       from_ggsns_read_cb, hub, plane_idx);
+		if (rc) {
+			LOGERR("Failed to bind for GGSNs (%s)\n",
+			       gtphub_plane_idx_names[plane_idx]);
+			return rc;
+		}
+
+		rc = gtphub_bind_start(&hub->to_sgsns[plane_idx],
+				       &cfg->to_sgsns[plane_idx],
+				       from_sgsns_read_cb, hub, plane_idx);
+		if (rc) {
+			LOGERR("Failed to bind for SGSNs (%s)\n",
+			       gtphub_plane_idx_names[plane_idx]);
+			return rc;
+		}
+	}
+
+
+	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
+		if (gtphub_make_proxy(hub,
+				      &hub->sgsn_proxy[plane_idx],
+				      &hub->to_sgsns[plane_idx],
+				      &cfg->sgsn_proxy[plane_idx])
+		    != 0) {
+			LOGERR("Cannot configure SGSN proxy %s port %d.\n",
+			       cfg->sgsn_proxy[plane_idx].addr_str,
+			       (int)cfg->sgsn_proxy[plane_idx].port);
+			return -1;
+		}
+		if (gtphub_make_proxy(hub,
+				      &hub->ggsn_proxy[plane_idx],
+				      &hub->to_ggsns[plane_idx],
+				      &cfg->ggsn_proxy[plane_idx])
+		    != 0) {
+			LOGERR("Cannot configure GGSN proxy.\n");
+			return -1;
+		}
+	}
+
+	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
+		if (hub->sgsn_proxy[plane_idx])
+			LOG("Using SGSN %s proxy %s\n",
+			    gtphub_plane_idx_names[plane_idx],
+			    gtphub_port_str(hub->sgsn_proxy[plane_idx]));
+	}
+
+	for (plane_idx = 0; plane_idx < GTPH_PLANE_N; plane_idx++) {
+		if (hub->sgsn_proxy[plane_idx])
+			LOG("Using GGSN %s proxy %s\n",
+			    gtphub_plane_idx_names[plane_idx],
+			    gtphub_port_str(hub->ggsn_proxy[plane_idx]));
+	}
+
+	gtphub_gc_start(hub);
+	return 0;
+}
+
+static struct gtphub_peer_addr *gtphub_peer_find_addr(const struct gtphub_peer *peer,
+						      const struct gsn_addr *addr)
+{
+	struct gtphub_peer_addr *a;
+	llist_for_each_entry(a, &peer->addresses, entry) {
+		if (gsn_addr_same(&a->addr, addr))
+			return a;
+	}
+	return NULL;
+}
+
+static struct gtphub_peer_port *gtphub_addr_find_port(const struct gtphub_peer_addr *a,
+						      uint16_t port)
+{
+	OSMO_ASSERT(port);
+	struct gtphub_peer_port *pp;
+	llist_for_each_entry(pp, &a->ports, entry) {
+		if (pp->port == port)
+			return pp;
+	}
+	return NULL;
+}
+
+static struct gtphub_peer_addr *gtphub_addr_find(const struct gtphub_bind *bind,
+						 const struct gsn_addr *addr)
+{
+	struct gtphub_peer *peer;
+	llist_for_each_entry(peer, &bind->peers, entry) {
+		struct gtphub_peer_addr *a = gtphub_peer_find_addr(peer, addr);
+		if (a)
+			return a;
+	}
+	return NULL;
+}
+
+static struct gtphub_peer_port *gtphub_port_find(const struct gtphub_bind *bind,
+						 const struct gsn_addr *addr,
+						 uint16_t port)
+{
+	struct gtphub_peer_addr *a = gtphub_addr_find(bind, addr);
+	if (!a)
+		return NULL;
+	return gtphub_addr_find_port(a, port);
+}
+
+struct gtphub_peer_port *gtphub_port_find_sa(const struct gtphub_bind *bind,
+					     const struct osmo_sockaddr *addr)
+{
+	struct gsn_addr gsna;
+	uint16_t port;
+	gsn_addr_from_sockaddr(&gsna, &port, addr);
+	return gtphub_port_find(bind, &gsna, port);
+}
+
+static struct gtphub_peer *gtphub_peer_new(struct gtphub *hub,
+					   struct gtphub_bind *bind)
+{
+	struct gtphub_peer *peer = talloc_zero(osmo_gtphub_ctx, struct gtphub_peer);
+	OSMO_ASSERT(peer);
+
+	INIT_LLIST_HEAD(&peer->addresses);
+
+	nr_pool_init(&peer->seq_pool);
+	nr_map_init(&peer->seq_map, &peer->seq_pool, &hub->expire_seq_maps);
+
+	/* TODO use something random to pick the initial sequence nr.
+	   0x6d31 produces the ASCII character sequence 'm1', currently used in
+	   gtphub_nc_test.sh. */
+	peer->seq_pool.last_nr = 0x6d31 - 1;
+
+	llist_add(&peer->entry, &bind->peers);
+	return peer;
+}
+
+static struct gtphub_peer_addr *gtphub_peer_add_addr(struct gtphub_peer *peer,
+						     const struct gsn_addr *addr)
+{
+	struct gtphub_peer_addr *a;
+	a = talloc_zero(osmo_gtphub_ctx, struct gtphub_peer_addr);
+	OSMO_ASSERT(a);
+	a->peer = peer;
+	gsn_addr_copy(&a->addr, addr);
+	INIT_LLIST_HEAD(&a->ports);
+	llist_add(&a->entry, &peer->addresses);
+
+	return a;
+}
+
+static struct gtphub_peer_addr *gtphub_addr_have(struct gtphub *hub,
+						 struct gtphub_bind *bind,
+						 const struct gsn_addr *addr)
+{
+	struct gtphub_peer_addr *a = gtphub_addr_find(bind, addr);
+	if (a)
+		return a;
+
+	/* If we haven't found an address, that means we need to create an
+	 * entirely new peer for the new address. More addresses may be added
+	 * to this peer later, but not via this function. */
+	struct gtphub_peer *peer = gtphub_peer_new(hub, bind);
+	return gtphub_peer_add_addr(peer, addr);
+}
+
+static struct gtphub_peer_port *gtphub_addr_add_port(struct gtphub_peer_addr *a,
+						     uint16_t port)
+{
+	struct gtphub_peer_port *pp;
+
+	pp = talloc_zero(osmo_gtphub_ctx, struct gtphub_peer_port);
+	OSMO_ASSERT(pp);
+	pp->peer_addr = a;
+	pp->port = port;
+
+	if (gsn_addr_to_sockaddr(&a->addr, port, &pp->sa) != 0) {
+		talloc_free(pp);
+		return NULL;
+	}
+
+	llist_add(&pp->entry, &a->ports);
+
+	LOG("New peer: %s port %d\n",
+	    gsn_addr_to_str(&a->addr),
+	    (int)port);
+
+	return pp;
+}
+
+static struct gtphub_peer_port *gtphub_port_have(struct gtphub *hub,
+						 struct gtphub_bind *bind,
+						 const struct gsn_addr *addr,
+						 uint16_t port)
+{
+	struct gtphub_peer_addr *a = gtphub_addr_have(hub, bind, addr);
+
+	struct gtphub_peer_port *pp = gtphub_addr_find_port(a, port);
+	if (pp)
+		return pp;
+
+	return gtphub_addr_add_port(a, port);
+}
+
+/* port_override: <=0: use port from addr; >0: use this number as port. Return
+ * NULL if the address cannot be parsed. */
+static struct gtphub_peer_port *gtphub_port_have_sockaddr(struct gtphub *hub,
+							  struct gtphub_bind *bind,
+							  const struct osmo_sockaddr *addr,
+							  int port_override)
+{
+	struct gsn_addr gsna;
+	uint16_t port;
+	if (gsn_addr_from_sockaddr(&gsna, &port, addr) != 0)
+		return NULL;
+
+	if (port_override > 0)
+		port = port_override;
+	return gtphub_port_have(hub, bind, &gsna, port);
+}
+
+static struct gtphub_peer_port *gtphub_have_ggsn(struct gtphub *hub,
+						 struct osmo_sockaddr *addr,
+						 unsigned int plane_idx,
+						 int port_override)
+{
+	if (port_override == 0)
+		port_override = gtphub_plane_idx_default_port[plane_idx];
+
+	return gtphub_port_have_sockaddr(hub, &hub->to_ggsns[plane_idx], addr,
+					 port_override);
+}
+
+static struct gtphub_peer_port *gtphub_resolve_ggsn(struct gtphub *hub,
+						    struct gtp_packet_desc *p)
+{
+	int rc;
+
+	struct osmo_sockaddr addr;
+
+	rc = gtphub_resolve_ggsn_addr(hub, &addr, p);
+	if (rc < 0)
+		return NULL;
+
+	return gtphub_have_ggsn(hub, &addr, p->plane_idx, -1);
+}
+
+
+/* TODO move to osmocom/core/socket.c ? */
+/* The caller is required to call freeaddrinfo(*result), iff zero is returned. */
+/* use this in osmo_sock_init() to remove dup. */
+static int _osmo_getaddrinfo(struct addrinfo **result,
+			     uint16_t family, uint16_t type, uint8_t proto,
+			     const char *host, uint16_t port)
+{
+	struct addrinfo hints;
+	char portbuf[16];
+
+	sprintf(portbuf, "%u", port);
+	memset(&hints, '\0', sizeof(struct addrinfo));
+	hints.ai_family = family;
+	if (type == SOCK_RAW) {
+		/* Workaround for glibc, that returns EAI_SERVICE (-8) if
+		 * SOCK_RAW and IPPROTO_GRE is used.
+		 */
+		hints.ai_socktype = SOCK_DGRAM;
+		hints.ai_protocol = IPPROTO_UDP;
+	} else {
+		hints.ai_socktype = type;
+		hints.ai_protocol = proto;
+	}
+
+	return getaddrinfo(host, portbuf, &hints, result);
+}
+
+/* TODO move to osmocom/core/socket.c ? */
+int osmo_sockaddr_init(struct osmo_sockaddr *addr,
+		       uint16_t family, uint16_t type, uint8_t proto,
+		       const char *host, uint16_t port)
+{
+	struct addrinfo *res;
+	int rc;
+	rc = _osmo_getaddrinfo(&res, family, type, proto, host, port);
+
+	if (rc != 0) {
+		LOGERR("getaddrinfo returned error %d\n", (int)rc);
+		return -EINVAL;
+	}
+
+	OSMO_ASSERT(res->ai_addrlen <= sizeof(addr->a));
+	memcpy(&addr->a, res->ai_addr, res->ai_addrlen);
+	addr->l = res->ai_addrlen;
+	freeaddrinfo(res);
+
+	return 0;
+}
+
+int osmo_sockaddr_to_strs(char *addr_str, size_t addr_str_len,
+			  char *port_str, size_t port_str_len,
+			  const struct osmo_sockaddr *addr,
+			  int flags)
+{
+       int rc;
+
+       if ((addr->l < 1) || (addr->l > sizeof(addr->a))) {
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address size: %d\n", addr->l);
+	       return -1;
+       }
+
+       if (addr->l > sizeof(addr->a)) {
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address: too long: %d\n", addr->l);
+	       return -1;
+       }
+
+       rc = getnameinfo((struct sockaddr*)&addr->a, addr->l,
+			addr_str, addr_str_len,
+			port_str, port_str_len,
+			flags);
+
+       if (rc)
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address: %s: %s\n", gai_strerror(rc),
+		    osmo_hexdump((uint8_t*)&addr->a, addr->l));
+
+       return rc;
+}
+
+const char *osmo_sockaddr_to_strb(const struct osmo_sockaddr *addr,
+				  char *buf, size_t buf_len)
+{
+	const int portbuf_len = 6;
+	OSMO_ASSERT(buf_len > portbuf_len);
+	char *portbuf = buf + buf_len - portbuf_len;
+	buf_len -= portbuf_len;
+	if (osmo_sockaddr_to_strs(buf, buf_len,
+				  portbuf, portbuf_len,
+				  addr,
+				  NI_NUMERICHOST | NI_NUMERICSERV))
+		return NULL;
+
+	char *pos = buf + strnlen(buf, buf_len-1);
+	size_t len = buf_len - (pos - buf);
+
+	snprintf(pos, len, " port %s", portbuf);
+	buf[buf_len-1] = '\0';
+
+	return buf;
+}
+
+const char *osmo_sockaddr_to_str(const struct osmo_sockaddr *addr)
+{
+	static char buf[256];
+	const char *result = osmo_sockaddr_to_strb(addr, buf, sizeof(buf));
+	if (! result)
+		return "(invalid)";
+	return result;
+}
+
+int osmo_sockaddr_cmp(const struct osmo_sockaddr *a, const struct osmo_sockaddr *b)
+{
+	if (a == b)
+		return 0;
+	if (!a)
+		return -1;
+	if (!b)
+		return 1;
+	if (a->l != b->l) {
+		/* Lengths are not the same, but determine the order. Will
+		 * anyone ever sort a list by osmo_sockaddr though...? */
+		int cmp = memcmp(&a->a, &b->a, (a->l < b->l)? a->l : b->l);
+		if (cmp == 0) {
+			if (a->l < b->l)
+				return -1;
+			else
+				return 1;
+		}
+		return cmp;
+	}
+	return memcmp(&a->a, &b->a, a->l);
+}
+
+void osmo_sockaddr_copy(struct osmo_sockaddr *dst, const struct osmo_sockaddr *src)
+{
+	OSMO_ASSERT(src->l <= sizeof(dst->a));
+	memcpy(&dst->a, &src->a, src->l);
+	dst->l = src->l;
+}
diff --git a/openbsc/src/gprs/gtphub_ext.c b/openbsc/src/gprs/gtphub_ext.c
new file mode 100644
index 0000000..0a4164c
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_ext.c
@@ -0,0 +1,58 @@
+/* GTP Hub Implementation */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * gtphub_ext.c -- ext means extern. This file is kept separate so that these
+ * functions can be wrapped for gtphub_test.c. When a function and its callers
+ * are in the same compilational unit, the wrappability may be optimized away.
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+
+#include <openbsc/gtphub.h>
+#include <osmocom/core/utils.h>
+
+#define __llist_first(head) (((head)->next == (head)) ? NULL : (head)->next)
+#define llist_first(head, type, entry) llist_entry(__llist_first(head), type, entry)
+
+int gtphub_resolve_ggsn_addr(struct gtphub *hub,
+			     struct osmo_sockaddr *result,
+			     struct gtp_packet_desc *p)
+{
+	/* TODO  This is just hardcodedly returning the first known address.
+	 * Should resolve from actual subscriber data. */
+	struct gtphub_peer *peer = llist_first(&hub->to_ggsns[GTPH_PLANE_CTRL].peers,
+					       struct gtphub_peer, entry);
+	if (!peer)
+		return -1;
+
+	struct gtphub_peer_addr *pa = llist_first(&peer->addresses,
+						  struct gtphub_peer_addr, entry);
+	if (!pa)
+		return -1;
+
+	struct gtphub_peer_port *pp = llist_first(&pa->ports,
+						  struct gtphub_peer_port, entry);
+	if (!pp)
+		return -1;
+
+	*result = pp->sa;
+	return 0;
+}
+
diff --git a/openbsc/src/gprs/gtphub_main.c b/openbsc/src/gprs/gtphub_main.c
new file mode 100644
index 0000000..e0df0d6
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_main.c
@@ -0,0 +1,282 @@
+/* GTP Hub main program */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <unistd.h>
+#include <signal.h>
+#include <string.h>
+#include <errno.h>
+
+#define _GNU_SOURCE
+#include <getopt.h>
+
+#include <osmocom/core/signal.h>
+#include <osmocom/core/application.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/rate_ctr.h>
+
+#include <osmocom/vty/logging.h>
+#include <osmocom/vty/telnet_interface.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gtphub.h>
+#include <openbsc/vty.h>
+
+#include "../../bscconfig.h"
+
+#define LOGERR(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_ERROR, fmt, ##args)
+
+#define LOG(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_NOTICE, fmt, ##args)
+
+#ifndef OSMO_VTY_PORT_GTPHUB
+/* should come from libosmocore */
+#define OSMO_VTY_PORT_GTPHUB	4253
+#endif
+
+extern void *osmo_gtphub_ctx;
+
+
+const char *gtphub_copyright =
+	"Copyright (C) 2015 sysmocom s.f.m.c GmbH <info@sysmocom.de>\r\n"
+	"License AGPLv3+: GNU AGPL version 2 or later <http://gnu.org/licenses/agpl-3.0.html>\r\n"
+	"This is free software: you are free to change and redistribute it.\r\n"
+	"There is NO WARRANTY, to the extent permitted by law.\r\n";
+
+static struct log_info_cat gtphub_categories[] = {
+	[DGTPHUB] = {
+		.name = "DGTPHUB",
+		.description = "GTP Hub",
+		.color = "\033[1;33m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+int gtphub_log_filter_fn(const struct log_context *ctx,
+			 struct log_target *tar)
+{
+	return 0;
+}
+
+static const struct log_info gtphub_log_info = {
+	.filter_fn = gtphub_log_filter_fn,
+	.cat = gtphub_categories,
+	.num_cat = ARRAY_SIZE(gtphub_categories),
+};
+
+void log_cfg(struct gtphub_cfg *cfg)
+{
+	struct gtphub_cfg_addr *a;
+	a = &cfg->to_sgsns[GTPH_PLANE_CTRL].bind;
+	LOG("to-SGSNs bind, Control: %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_sgsns[GTPH_PLANE_USER].bind;
+	LOG("to-SGSNs bind, User:    %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_ggsns[GTPH_PLANE_CTRL].bind;
+	LOG("to-GGSNs bind, Control: %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_ggsns[GTPH_PLANE_USER].bind;
+	LOG("to-GGSNs bind, User:    %s port %d\n",
+	    a->addr_str, a->port);
+}
+
+static void signal_handler(int signal)
+{
+	fprintf(stdout, "signal %u received\n", signal);
+
+	switch (signal) {
+	case SIGINT:
+		osmo_signal_dispatch(SS_L_GLOBAL, S_L_GLOBAL_SHUTDOWN, NULL);
+		sleep(1);
+		exit(0);
+		break;
+	case SIGABRT:
+		/* in case of abort, we want to obtain a talloc report
+		 * and then return to the caller, who will abort the process */
+	case SIGUSR1:
+	case SIGUSR2:
+		talloc_report_full(osmo_gtphub_ctx, stderr);
+		break;
+	default:
+		break;
+	}
+}
+
+extern int bsc_vty_go_parent(struct vty *vty);
+
+static struct vty_app_info vty_info = {
+	.name 		= "OsmoGTPhub",
+	.version	= PACKAGE_VERSION,
+	.go_parent_cb	= bsc_vty_go_parent,
+	.is_config_node	= bsc_vty_is_config_node,
+};
+
+struct cmdline_cfg {
+	const char *config_file;
+	int daemonize;
+};
+
+static void print_help(struct cmdline_cfg *ccfg)
+{
+	printf("gtphub commandline options\n");
+	printf("  -h --help            This text.\n");
+	printf("  -D --daemonize       Fork the process into a background daemon.\n");
+	printf("  -d,--debug <cat>     Enable Debugging for this category.\n");
+	printf("                       Pass '-d list' to get a category listing.\n");
+	printf("  -s --disable-color");
+	printf("  -c --config-file     The config file to use [%s].\n", ccfg->config_file);
+	printf("  -e,--log-level <nr>  Set a global log level.\n");
+}
+
+static void list_categories(void)
+{
+	printf("Avaliable debug categories:\n");
+	int i;
+	for (i = 0; i < gtphub_log_info.num_cat; ++i) {
+		if (!gtphub_log_info.cat[i].name)
+			continue;
+
+		printf("%s\n", gtphub_log_info.cat[i].name);
+	}
+}
+
+static void handle_options(struct cmdline_cfg *ccfg, int argc, char **argv)
+{
+	while (1) {
+		int option_index = 0, c;
+		static struct option long_options[] = {
+			{"help", 0, 0, 'h'},
+			{"debug", 1, 0, 'd'},
+			{"daemonize", 0, 0, 'D'},
+			{"config-file", 1, 0, 'c'},
+			{"disable-color", 0, 0, 's'},
+			{"timestamp", 0, 0, 'T'},
+			{"log-level", 1, 0, 'e'},
+			{NULL, 0, 0, 0}
+		};
+
+		c = getopt_long(argc, argv, "hd:Dc:sTe:",
+				long_options, &option_index);
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'h':
+			//print_usage();
+			print_help(ccfg);
+			exit(0);
+		case 's':
+			log_set_use_color(osmo_stderr_target, 0);
+			break;
+		case 'd':
+			if (strcmp("list", optarg) == 0) {
+				list_categories();
+				exit(0);
+			} else
+				log_parse_category_mask(osmo_stderr_target, optarg);
+			break;
+		case 'D':
+			ccfg->daemonize = 1;
+			break;
+		case 'c':
+			ccfg->config_file = optarg;
+			break;
+		case 'T':
+			log_set_print_timestamp(osmo_stderr_target, 1);
+			break;
+		case 'e':
+			log_set_log_level(osmo_stderr_target, atoi(optarg));
+			break;
+		default:
+			/* ignore */
+			break;
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int rc;
+
+	osmo_gtphub_ctx = talloc_named_const(NULL, 0, "osmo_gtphub");
+
+	signal(SIGINT, &signal_handler);
+	signal(SIGABRT, &signal_handler);
+	signal(SIGUSR1, &signal_handler);
+	signal(SIGUSR2, &signal_handler);
+	osmo_init_ignore_signals();
+
+	osmo_init_logging(&gtphub_log_info);
+
+	vty_info.copyright = gtphub_copyright;
+	vty_init(&vty_info);
+	logging_vty_add_cmds(&gtphub_log_info);
+        gtphub_vty_init();
+
+	rate_ctr_init(osmo_gtphub_ctx);
+	rc = telnet_init(osmo_gtphub_ctx, 0, OSMO_VTY_PORT_GTPHUB);
+	if (rc < 0)
+		exit(1);
+
+	struct cmdline_cfg _ccfg;
+	struct cmdline_cfg *ccfg = &_ccfg;
+	memset(ccfg, '\0', sizeof(*ccfg));
+	ccfg->config_file = "./gtphub.conf";
+
+	struct gtphub_cfg _cfg;
+	struct gtphub_cfg *cfg = &_cfg;
+	memset(cfg, '\0', sizeof(*cfg));
+
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+
+	handle_options(ccfg, argc, argv);
+
+	rc = gtphub_cfg_read(cfg, ccfg->config_file);
+	if (rc < 0) {
+		LOGP(DGTPHUB, LOGL_FATAL, "Cannot parse config file '%s'\n", ccfg->config_file);
+		exit(2);
+	}
+
+	if (gtphub_start(hub, cfg) != 0)
+		return -1;
+
+	log_cfg(cfg);
+
+	if (ccfg->daemonize) {
+		rc = osmo_daemonize();
+		if (rc < 0) {
+			LOGERR("Error during daemonize");
+			exit(1);
+		}
+	}
+
+	while (1) {
+		rc = osmo_select_main(0);
+		if (rc < 0)
+			exit(3);
+	}
+
+	/* not reached */
+	exit(0);
+}
diff --git a/openbsc/src/gprs/gtphub_vty.c b/openbsc/src/gprs/gtphub_vty.c
new file mode 100644
index 0000000..aead178
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_vty.c
@@ -0,0 +1,258 @@
+/* (C) 2015 by sysmocom s.f.m.c. GmbH
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <string.h>
+
+#include <osmocom/core/talloc.h>
+#include <osmocom/vty/command.h>
+
+#include <openbsc/vty.h>
+#include <openbsc/gtphub.h>
+
+static struct gtphub_cfg *g_cfg = 0;
+
+static struct cmd_node gtphub_node = {
+	GTPHUB_NODE,
+	"%s(config-gtphub)# ",
+	1,
+};
+
+#define GTPH_DEFAULT_CONTROL_PORT 2123
+#define GTPH_DEFAULT_USER_PORT 2152
+
+static void write_addrs(struct vty *vty, const char *name,
+			struct gtphub_cfg_addr *c, struct gtphub_cfg_addr *u)
+{
+	if ((c->port == GTPH_DEFAULT_CONTROL_PORT)
+	    && (u->port == GTPH_DEFAULT_USER_PORT)
+	    && (strcmp(c->addr_str, u->addr_str) == 0)) {
+		/* Default port numbers and same IP address: write "short"
+		 * variant. */
+		vty_out(vty, " %s %s%s",
+			name,
+			c->addr_str,
+			VTY_NEWLINE);
+		return;
+	}
+
+	vty_out(vty, " %s ctrl %s %d user %s %d%s",
+		name,
+		c->addr_str, (int)c->port,
+		u->addr_str, (int)u->port,
+		VTY_NEWLINE);
+}
+
+static int config_write_gtphub(struct vty *vty)
+{
+	vty_out(vty, "gtphub%s", VTY_NEWLINE);
+
+	write_addrs(vty, "bind-to-sgsns",
+		    &g_cfg->to_sgsns[GTPH_PLANE_CTRL].bind,
+		    &g_cfg->to_sgsns[GTPH_PLANE_USER].bind);
+
+	write_addrs(vty, "bind-to-ggsns",
+		    &g_cfg->to_ggsns[GTPH_PLANE_CTRL].bind,
+		    &g_cfg->to_ggsns[GTPH_PLANE_USER].bind);
+
+	if (g_cfg->ggsn_proxy[GTPH_PLANE_CTRL].addr_str) {
+		write_addrs(vty, "ggsn-proxy",
+			    &g_cfg->ggsn_proxy[GTPH_PLANE_CTRL],
+			    &g_cfg->ggsn_proxy[GTPH_PLANE_USER]);
+	}
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub, cfg_gtphub_cmd,
+      "gtphub",
+      "Configure the GTP hub")
+{
+	vty->node = GTPHUB_NODE;
+	return CMD_SUCCESS;
+}
+
+#define BIND_ARGS  "ctrl ADDR <0-65535> user ADDR <0-65535>"
+#define BIND_DOCS  \
+	"Set GTP-C bind\n" \
+	"GTP-C local IP address (v4 or v6)\n" \
+	"GTP-C local port\n" \
+	"Set GTP-U bind\n" \
+	"GTP-U local IP address (v4 or v6)\n" \
+	"GTP-U local port\n"
+
+
+DEFUN(cfg_gtphub_bind_to_sgsns_short, cfg_gtphub_bind_to_sgsns_short_cmd,
+	"bind-to-sgsns ADDR",
+	"GTP Hub Parameters\n"
+	"Set the local bind address to listen for SGSNs, for both GTP-C and GTP-U\n"
+	"Local IP address (v4 or v6)\n"
+	)
+{
+	int i;
+	for (i = 0; i < GTPH_PLANE_N; i++)
+		g_cfg->to_sgsns[i].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->to_sgsns[GTPH_PLANE_CTRL].bind.port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->to_sgsns[GTPH_PLANE_USER].bind.port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_bind_to_ggsns_short, cfg_gtphub_bind_to_ggsns_short_cmd,
+	"bind-to-ggsns ADDR",
+	"GTP Hub Parameters\n"
+	"Set the local bind address to listen for GGSNs, for both GTP-C and GTP-U\n"
+	"Local IP address (v4 or v6)\n"
+	)
+{
+	int i;
+	for (i = 0; i < GTPH_PLANE_N; i++)
+		g_cfg->to_ggsns[i].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->to_ggsns[GTPH_PLANE_CTRL].bind.port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->to_ggsns[GTPH_PLANE_USER].bind.port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+
+static int handle_binds(struct gtphub_cfg_bind *b, const char **argv)
+{
+	b[GTPH_PLANE_CTRL].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	b[GTPH_PLANE_CTRL].bind.port = atoi(argv[1]);
+	b[GTPH_PLANE_USER].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	b[GTPH_PLANE_USER].bind.port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_bind_to_sgsns, cfg_gtphub_bind_to_sgsns_cmd,
+	"bind-to-sgsns " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Set the local bind addresses and ports to listen for SGSNs\n"
+	BIND_DOCS
+	)
+{
+	return handle_binds(g_cfg->to_sgsns, argv);
+}
+
+DEFUN(cfg_gtphub_bind_to_ggsns, cfg_gtphub_bind_to_ggsns_cmd,
+	"bind-to-ggsns " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Set the local bind addresses and ports to listen for GGSNs\n"
+	BIND_DOCS
+	)
+{
+	return handle_binds(g_cfg->to_ggsns, argv);
+}
+
+DEFUN(cfg_gtphub_ggsn_proxy_short, cfg_gtphub_ggsn_proxy_short_cmd,
+	"ggsn-proxy ADDR",
+	"GTP Hub Parameters\n"
+	"Redirect all GGSN bound traffic to default ports on this address (another gtphub)\n"
+	"Remote IP address (v4 or v6)\n"
+	)
+{
+	g_cfg->ggsn_proxy[GTPH_PLANE_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PLANE_CTRL].port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->ggsn_proxy[GTPH_PLANE_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PLANE_USER].port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_ggsn_proxy, cfg_gtphub_ggsn_proxy_cmd,
+	"ggsn-proxy " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Redirect all GGSN bound traffic to these addresses and ports (another gtphub)\n"
+	BIND_DOCS
+	)
+{
+	g_cfg->ggsn_proxy[GTPH_PLANE_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PLANE_CTRL].port = atoi(argv[1]);
+	g_cfg->ggsn_proxy[GTPH_PLANE_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	g_cfg->ggsn_proxy[GTPH_PLANE_USER].port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_sgsn_proxy_short, cfg_gtphub_sgsn_proxy_short_cmd,
+	"sgsn-proxy ADDR",
+	"GTP Hub Parameters\n"
+	"Redirect all SGSN bound traffic to default ports on this address (another gtphub)\n"
+	"Remote IP address (v4 or v6)\n"
+	)
+{
+	g_cfg->sgsn_proxy[GTPH_PLANE_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PLANE_CTRL].port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->sgsn_proxy[GTPH_PLANE_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PLANE_USER].port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_sgsn_proxy, cfg_gtphub_sgsn_proxy_cmd,
+	"sgsn-proxy " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Redirect all SGSN bound traffic to these addresses and ports (another gtphub)\n"
+	BIND_DOCS
+	)
+{
+	g_cfg->sgsn_proxy[GTPH_PLANE_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PLANE_CTRL].port = atoi(argv[1]);
+	g_cfg->sgsn_proxy[GTPH_PLANE_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	g_cfg->sgsn_proxy[GTPH_PLANE_USER].port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(show_gtphub, show_gtphub_cmd, "show gtphub",
+      SHOW_STR "Display information about the GTP hub")
+{
+	vty_out(vty, "gtphub has nothing to say yet%s", VTY_NEWLINE);
+	return CMD_SUCCESS;
+}
+
+
+int gtphub_vty_init(void)
+{
+	install_element_ve(&show_gtphub_cmd);
+
+	install_element(CONFIG_NODE, &cfg_gtphub_cmd);
+	install_node(&gtphub_node, config_write_gtphub);
+	vty_install_default(GTPHUB_NODE);
+
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_sgsns_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_sgsns_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_ggsns_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_ggsns_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_ggsn_proxy_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_ggsn_proxy_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_sgsn_proxy_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_sgsn_proxy_cmd);
+
+	return 0;
+}
+
+int gtphub_cfg_read(struct gtphub_cfg *cfg, const char *config_file)
+{
+	int rc;
+
+	g_cfg = cfg;
+
+	rc = vty_read_config_file(config_file, NULL);
+	if (rc < 0) {
+		fprintf(stderr, "Failed to parse the config file: '%s'\n", config_file);
+		return rc;
+	}
+
+	return 0;
+}
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 1b557d4..aacfe0b 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr oap
+SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr oap gtphub
 
 if BUILD_NAT
 SUBDIRS += bsc-nat bsc-nat-trie
diff --git a/openbsc/tests/gtphub/Makefile.am b/openbsc/tests/gtphub/Makefile.am
new file mode 100644
index 0000000..ecc6d62
--- /dev/null
+++ b/openbsc/tests/gtphub/Makefile.am
@@ -0,0 +1,20 @@
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include
+AM_CFLAGS=-Wall -ggdb3 $(LIBOSMOCORE_CFLAGS)
+
+EXTRA_DIST = \
+	gtphub_test.ok \
+	gtphub_nc_test.sh \
+	gtphub_nc_test.ok \
+	hex2bin.py
+
+noinst_PROGRAMS = gtphub_test
+
+gtphub_test_SOURCES = gtphub_test.c
+gtphub_test_LDFLAGS = \
+	-Wl,--wrap=gtphub_resolve_ggsn_addr
+
+gtphub_test_LDADD = \
+	$(top_builddir)/src/gprs/gtphub.o \
+	$(LIBOSMOCORE_LIBS) \
+	-lgtp -lrt
+
diff --git a/openbsc/tests/gtphub/gtphub_test.c b/openbsc/tests/gtphub/gtphub_test.c
new file mode 100644
index 0000000..af8f3ed
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_test.c
@@ -0,0 +1,709 @@
+/* Test the GTP hub */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmcom.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <unistd.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/application.h>
+
+#include <openbsc/debug.h>
+
+#include <openbsc/gtphub.h>
+#include <gtp.h>
+#include <gtpie.h>
+
+#define EXPIRE_ALL ((60 * GTPH_TEI_MAPPING_EXPIRY_MINUTES) + 1)
+
+/* Make non-public API accessible */
+
+void gtphub_init(struct gtphub *hub);
+
+void *osmo_gtphub_ctx;
+
+/* TODO copied from libosmo-abis/src/subchan_demux.c, remove dup */
+static int llist_len(struct llist_head *head)
+{
+	struct llist_head *entry;
+	int i = 0;
+
+	llist_for_each(entry, head)
+		i++;
+
+	return i;
+}
+
+static void nr_mapping_free(struct expiring_item *e)
+{
+	struct nr_mapping *m = container_of(e, struct nr_mapping,
+					    expiry_entry);
+	nr_mapping_del(m);
+	talloc_free(m);
+}
+
+static struct nr_mapping *nr_mapping_alloc(void)
+{
+	struct nr_mapping *m;
+	m = talloc(osmo_gtphub_ctx, struct nr_mapping);
+	nr_mapping_init(m);
+	m->expiry_entry.del_cb = nr_mapping_free;
+	return m;
+}
+
+static struct nr_mapping *nr_map_have(struct nr_map *map, void *origin, nr_t orig, time_t now)
+{
+	struct nr_mapping *mapping;
+
+	mapping = nr_map_get(map, origin, orig);
+	if (!mapping) {
+		mapping = nr_mapping_alloc();
+		mapping->origin = origin;
+		mapping->orig = orig;
+		nr_map_add(map, mapping, now);
+	}
+
+	return mapping;
+}
+
+static nr_t nr_map_verify(const struct nr_map *map, void *origin, nr_t orig, nr_t expect_repl)
+{
+	struct nr_mapping *m;
+	m = nr_map_get(map, origin, orig);
+
+	if (!m) {
+		printf("mapping not found for %p %d\n", origin, orig);
+		return 0;
+	}
+
+	if (m->repl != expect_repl) {
+		printf("mapping found, but nr mismatches: expect %d, got %d\n",
+		       (int)expect_repl, (int)m->repl);
+		return 0;
+	}
+
+	return 1;
+}
+
+static int nr_map_verify_inv(const struct nr_map *map, nr_t repl,
+			     void *expect_origin, nr_t expect_orig)
+{
+	struct nr_mapping *m;
+	m = nr_map_get_inv(map, repl);
+	if (!m) {
+		printf("mapping not found for %d\n", (int)repl);
+		return 0;
+	}
+
+	if (m->origin != expect_origin) {
+		printf("mapping found, but origin mismatches: expect %p, got %p\n",
+		       expect_origin, m->origin);
+		return 0;
+	}
+
+	if (m->orig != expect_orig) {
+		printf("mapping found, but nr mismatches: expect %d, got %d\n",
+		       (int)expect_orig, (int)m->orig);
+		return 0;
+	}
+
+	return 1;
+}
+
+
+static void test_nr_map_basic(void)
+{
+	struct nr_pool _pool;
+	struct nr_pool *pool = &_pool;
+	struct nr_map _map;
+	struct nr_map *map = &_map;
+
+	nr_pool_init(pool);
+	nr_map_init(map, pool, NULL);
+
+	OSMO_ASSERT(llist_empty(&map->mappings));
+
+#define TEST_N_HALF 100
+#define TEST_N (2*TEST_N_HALF)
+#define TEST_I 123
+	uint32_t i, check_i;
+	uint32_t m[TEST_N];
+	struct nr_mapping *mapping;
+
+	/* create half of TEST_N mappings from one origin */
+	void *origin1 = (void*)0x1234;
+	for (i = 0; i < TEST_N_HALF; i++) {
+		nr_t orig = TEST_I + i;
+		mapping = nr_map_have(map, origin1, orig, 0);
+		m[i] = mapping->repl;
+		OSMO_ASSERT(m[i] != 0);
+		OSMO_ASSERT(llist_len(&map->mappings) == (i+1));
+		for (check_i = 0; check_i < i; check_i++)
+			OSMO_ASSERT(m[check_i] != m[i]);
+	}
+	OSMO_ASSERT(llist_len(&map->mappings) == TEST_N_HALF);
+
+	/* create another TEST_N mappings with the same original numbers, but
+	 * from a different origin */
+	void *origin2 = (void*)0x5678;
+	for (i = 0; i < TEST_N_HALF; i++) {
+		int i2 = TEST_N_HALF + i;
+		nr_t orig = TEST_I + i;
+		mapping = nr_map_have(map, origin2, orig, 0);
+		m[i2] = mapping->repl;
+		OSMO_ASSERT(m[i2] != 0);
+		OSMO_ASSERT(llist_len(&map->mappings) == (i2+1));
+		for (check_i = 0; check_i < i2; check_i++)
+			OSMO_ASSERT(m[check_i] != m[i2]);
+	}
+	OSMO_ASSERT(llist_len(&map->mappings) == TEST_N);
+
+	/* verify mappings */
+	for (i = 0; i < TEST_N_HALF; i++) {
+		nr_t orig = TEST_I + i;
+		{
+			OSMO_ASSERT(nr_map_verify(map, origin1, orig, m[i]));
+			OSMO_ASSERT(nr_map_verify_inv(map, m[i], origin1, orig));
+		}
+		{
+			int i2 = TEST_N_HALF + i;
+			OSMO_ASSERT(nr_map_verify(map, origin2, orig, m[i2]));
+			OSMO_ASSERT(nr_map_verify_inv(map, m[i2], origin2, orig));
+		}
+	}
+
+	/* remove all mappings */
+	for (i = 0; i < TEST_N_HALF; i++) {
+		OSMO_ASSERT(llist_len(&map->mappings) == (TEST_N - 2*i));
+
+		nr_t orig = TEST_I + i;
+		nr_mapping_del(nr_map_get(map, origin1, orig));
+		nr_mapping_del(nr_map_get(map, origin2, orig));
+	}
+	OSMO_ASSERT(llist_empty(&map->mappings));
+#undef TEST_N
+#undef TEST_I
+}
+
+static int nr_map_is(struct nr_map *map, const char *str)
+{
+	static char buf[4096];
+	char *pos = buf;
+	size_t len = sizeof(buf);
+	struct nr_mapping *m;
+	llist_for_each_entry(m, &map->mappings, entry) {
+		size_t wrote = snprintf(pos, len, "(%d->%d@%d), ",
+					(int)m->orig,
+					(int)m->repl,
+					(int)m->expiry_entry.expiry);
+		OSMO_ASSERT(wrote < len);
+		pos += wrote;
+		len -= wrote;
+	}
+	*pos = '\0';
+
+	if (strncmp(buf, str, sizeof(buf)) != 0) {
+		printf("FAILURE: nr_map_is() mismatches expected value:\n"
+		       "expected: \"%s\"\n"
+		       "is:       \"%s\"\n",
+		       str, buf);
+		return 0;
+	}
+	return 1;
+}
+
+static void test_expiry(void)
+{
+	struct expiry expiry;
+	struct nr_pool pool;
+	struct nr_map map;
+	int i;
+
+	expiry_init(&expiry, 30);
+	nr_pool_init(&pool);
+	nr_map_init(&map, &pool, &expiry);
+	OSMO_ASSERT(nr_map_is(&map, ""));
+
+	/* tick on empty map */
+	OSMO_ASSERT(expiry_tick(&expiry, 10000) == 0);
+	OSMO_ASSERT(nr_map_is(&map, ""));
+
+#define MAP1 \
+	"(10->1@10040), " \
+	""
+
+#define MAP2 \
+	"(20->2@10050), " \
+	"(21->3@10051), " \
+	"(22->4@10052), " \
+	"(23->5@10053), " \
+	"(24->6@10054), " \
+	"(25->7@10055), " \
+	"(26->8@10056), " \
+	"(27->9@10057), " \
+	""
+
+#define MAP3 \
+	"(420->10@10072), " \
+	"(421->11@10072), " \
+	"(422->12@10072), " \
+	"(423->13@10072), " \
+	"(424->14@10072), " \
+	"(425->15@10072), " \
+	"(426->16@10072), " \
+	"(427->17@10072), " \
+	""
+
+	/* add mapping at time 10010. */
+	nr_map_have(&map, 0, 10, 10010);
+	OSMO_ASSERT(nr_map_is(&map, MAP1));
+
+	/* tick on unexpired item. */
+	OSMO_ASSERT(expiry_tick(&expiry, 10010) == 0);
+	OSMO_ASSERT(expiry_tick(&expiry, 10011) == 0);
+	OSMO_ASSERT(nr_map_is(&map, MAP1));
+
+	/* Spread mappings at 10020, 10021, ... 10027. */
+	for (i = 0; i < 8; i++)
+		nr_map_have(&map, 0, 20 + i, 10020 + i);
+	OSMO_ASSERT(nr_map_is(&map, MAP1 MAP2));
+
+	/* tick on unexpired items. */
+	OSMO_ASSERT(expiry_tick(&expiry, 10030) == 0);
+	OSMO_ASSERT(expiry_tick(&expiry, 10039) == 0);
+	OSMO_ASSERT(nr_map_is(&map, MAP1 MAP2));
+
+	/* expire the first item (from 10010). */
+	OSMO_ASSERT(expiry_tick(&expiry, 10010 + 30) == 1);
+	OSMO_ASSERT(nr_map_is(&map, MAP2));
+
+	/* again nothing to expire */
+	OSMO_ASSERT(expiry_tick(&expiry, 10041) == 0);
+	OSMO_ASSERT(nr_map_is(&map, MAP2));
+
+	/* Mappings all at the same time. */
+	for (i = 0; i < 8; i++)
+		nr_map_have(&map, 0, 420 + i, 10042);
+	OSMO_ASSERT(nr_map_is(&map, MAP2 MAP3));
+
+	/* Eight to expire, were added further above to be chronologically
+	 * correct, at 10020..10027. */
+	OSMO_ASSERT(expiry_tick(&expiry, 10027 + 30) == 8);
+	OSMO_ASSERT(nr_map_is(&map, MAP3));
+
+	/* again nothing to expire */
+	OSMO_ASSERT(expiry_tick(&expiry, 10027 + 30) == 0);
+	OSMO_ASSERT(nr_map_is(&map, MAP3));
+
+	/* Eight to expire, from 10042. Now at 10042 + 30: */
+	OSMO_ASSERT(expiry_tick(&expiry, 10042 + 30) == 8);
+	OSMO_ASSERT(nr_map_is(&map, ""));
+
+#undef MAP1
+#undef MAP2
+#undef MAP3
+}
+
+
+
+/* override, requires '-Wl,--wrap=gtphub_resolve_ggsn_addr' */
+int __real_gtphub_resolve_ggsn_addr(struct gtphub *hub,
+				    struct osmo_sockaddr *result,
+				    struct gtp_packet_desc *p);
+
+struct osmo_sockaddr resolved_ggsn_addr = {.l = 0};
+int __wrap_gtphub_resolve_ggsn_addr(struct gtphub *hub,
+				    struct osmo_sockaddr *result,
+				    struct gtp_packet_desc *p)
+{
+	osmo_sockaddr_copy(result, &resolved_ggsn_addr);
+	printf("Wrap: returning GGSN addr: %s\n",
+	       osmo_sockaddr_to_str(result));
+	return (resolved_ggsn_addr.l != 0)? 0 : -1;
+}
+
+#define buf_len 1024
+static uint8_t buf[buf_len];
+
+static unsigned int msg(const char *hex)
+{
+	unsigned int l = osmo_hexparse(hex, buf, buf_len);
+	OSMO_ASSERT(l > 0);
+	return l;
+}
+
+/* Compare static buf to given string constant. The amount of bytes is obtained
+ * from parsing the GTP header in buf.  hex must match an osmo_hexdump() of the
+ * desired message. Return 1 if size and content match. */
+#define msg_is(MSG) _msg_is(MSG, __FILE__, __LINE__)
+static int _msg_is(const char *hex, const char *file, int line)
+{
+	struct gtp1_header_long *h = (void*)buf;
+	int len = ntoh16(h->length) + 8;
+	const char *dump = osmo_hexdump_nospc(buf, len);
+	int cmp = strcmp(dump, hex);
+
+	if (cmp != 0) {
+		printf("\n%s:%d: msg_is(): MISMATCH\n"
+		       "  expecting:\n'%s'\n"
+		       "        got:\n'%s'\n\n",
+		       file,
+		       line,
+		       hex, dump);
+		int i;
+		int l = strlen(hex);
+		int m = strlen(dump);
+		if (m < l)
+			l = m;
+		for (i = 0; i < l; i++) {
+			if (hex[i] != dump[i]) {
+				printf("First mismatch at position %d:\n"
+				       "  %s\n  %s\n", i, hex + i, dump + i);
+				break;
+			}
+		}
+	}
+	return cmp == 0;
+}
+
+#define same_addr(GOT, EXPECTED) _same_addr((GOT),(EXPECTED), __FILE__, __LINE__)
+static int _same_addr(const struct osmo_sockaddr *got,
+		      const struct osmo_sockaddr *expected,
+		      const char *file, int line)
+{
+	int cmp = osmo_sockaddr_cmp(got, expected);
+	if (!cmp)
+		return 1;
+	char buf[256];
+	printf("\n%s:%d: addr_is(): MISMATCH\n"
+	       "  expecting: '%s'\n"
+	       "        got: '%s'\n\n",
+	       file, line,
+	       osmo_sockaddr_to_str(expected),
+	       osmo_sockaddr_to_strb(got, buf, sizeof(buf)));
+	return 0;
+}
+
+static void test_echo(void)
+{
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+	time_t now = 123;
+
+	gtphub_init(hub);
+
+	const char *gtp_ping_from_sgsn =
+		"32"	/* 0b001'1 0010: version 1, protocol GTP, with seq nr. */
+		"01"	/* type 01: Echo request */
+		"0004"	/* length of 4 after header TEI */
+		"00000000" /* header TEI == 0 in Echo */
+		"abcd"	/* some 16 octet sequence nr */
+		"0000"	/* N-PDU 0, no extension header (why is this here?) */
+		;
+
+	/* Same with mapped sequence number */
+	const char *gtp_ping_to_ggsn =
+		"32" "01" "0004" "00000000"
+		"6d31"	/* mapped seq */
+		"00" "00";
+
+	const char *gtp_pong_from_ggsn =
+		"32"
+		"02"	/* type 02: Echo response */
+		"0006"	/* len */
+		"00000000" /* tei */
+		"6d31"	/* mapped seq */
+		"0000"	/* ext */
+		"0e01"	/* 0e: Recovery, val == 1 */
+		;
+	/* Same with unmapped sequence number */
+	const char *gtp_pong_to_sgsn =
+		"32" "02" "0006" "00000000"
+		"abcd"	/* unmapped seq */
+		"00" "00" "0e01";
+
+	/* Set the GGSN address that gtphub is forced to resolve to. */
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&resolved_ggsn_addr,
+					   "192.168.43.34", 434)
+		    == 0);
+
+	/* according to spec, we'd always send to port 2123 instead...
+	struct osmo_sockaddr ggsn_standard_port;
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&ggsn_standard_port,
+					   "192.168.43.34", 2123)
+		    == 0);
+	 */
+
+	struct osmo_sockaddr orig_sgsn_addr;
+	OSMO_ASSERT(osmo_sockaddr_init(&orig_sgsn_addr,
+				       AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				       "192.168.42.23", 423) == 0);
+	struct osmo_fd *ggsn_ofd = NULL;
+	struct osmo_sockaddr ggsn_addr;
+	int send;
+	send = gtphub_from_sgsns_handle_buf(hub, GTPH_PLANE_CTRL, &orig_sgsn_addr,
+					    buf, msg(gtp_ping_from_sgsn), now,
+					    &ggsn_ofd, &ggsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(ggsn_addr.l);
+	OSMO_ASSERT(same_addr(&ggsn_addr, &resolved_ggsn_addr));
+	OSMO_ASSERT(msg_is(gtp_ping_to_ggsn));
+
+	struct osmo_fd *sgsn_ofd;
+	struct osmo_sockaddr sgsn_addr;
+	send = gtphub_from_ggsns_handle_buf(hub, GTPH_PLANE_CTRL, &ggsn_addr,
+					    buf, msg(gtp_pong_from_ggsn), now,
+					    &sgsn_ofd, &sgsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(same_addr(&sgsn_addr, &orig_sgsn_addr));
+	OSMO_ASSERT(msg_is(gtp_pong_to_sgsn));
+
+	struct gtphub_peer_port *ggsn_port =
+		gtphub_port_find_sa(&hub->to_ggsns[GTPH_PLANE_CTRL],
+				    &resolved_ggsn_addr);
+	OSMO_ASSERT(ggsn_port);
+	struct gtphub_peer *ggsn = ggsn_port->peer_addr->peer;
+	/* now == 123; now + 30 == 153. */
+	OSMO_ASSERT(nr_map_is(&ggsn->seq_map, "(43981->27953@153), "));
+
+	OSMO_ASSERT(nr_map_is(&hub->tei_map[GTPH_PLANE_CTRL], ""));
+	OSMO_ASSERT(nr_map_is(&hub->tei_map[GTPH_PLANE_USER], ""));
+
+	gtphub_gc(hub, now + EXPIRE_ALL);
+}
+
+static void test_create_pdp_ctx(void)
+{
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+	time_t now = 345;
+
+	gtphub_init(hub);
+
+	/* Tell this mock gtphub its local address for this test. */
+	OSMO_ASSERT(gsn_addr_from_str(&hub->to_sgsns[GTPH_PLANE_CTRL].local_addr,
+				      "127.0.1.1") == 0);
+	OSMO_ASSERT(gsn_addr_from_str(&hub->to_sgsns[GTPH_PLANE_USER].local_addr,
+				      "127.0.1.2") == 0);
+	OSMO_ASSERT(gsn_addr_from_str(&hub->to_ggsns[GTPH_PLANE_CTRL].local_addr,
+				      "127.0.2.1") == 0);
+	OSMO_ASSERT(gsn_addr_from_str(&hub->to_ggsns[GTPH_PLANE_USER].local_addr,
+				      "127.0.2.2") == 0);
+
+	/* This is copied from a packet that sgsnemu sends. */
+	const char *gtp_req_from_sgsn =
+		"32" 	/* 0b001'1 0010: version 1, protocol GTP, with seq nr. */
+		"10" 	/* type 16: Create PDP Context Request */
+		"0067"	/* length = 8 + 103 */
+		"00000000" /* No TEI yet */
+		"abcd"	/* Sequence nr */
+		"00"	/* N-PDU 0 */
+		"00"	/* No extensions */
+		/* IEs */
+		"02"	/* 2 = IMSI */
+		  "42000121436587f9"
+		"0e" "60" /* 14: Recovery = 96 */
+		"0f01"	/* 15: Selection mode = MS provided APN, subscription not verified*/
+		"10"	/* 16: TEI Data I */
+		  "00000123"
+		"11"	/* 17: TEI Control Plane */
+		  "00000321"
+		"1400"	/* 20: NSAPI = 0*/
+		"1a"	/* 26: Charging Characteristics */
+		  "0800"
+		"80"	/* 128: End User Address */
+		  "0002" /* length = 2: empty PDP Address */
+		  "f121" /* spare 0xf0, PDP organization 1, PDP type number 0x21 = 33 */
+		"83"	/* 131: Access Point Name */
+		  "0008" /* length = 8 */
+		  "696e7465726e6574" /* "internet" */
+		"84"	/* 132: Protocol Configuration Options */
+		  "0015" /* length = 21 */
+		  "80c0231101010011036d69670868656d6d656c6967"
+		"85"	/* 133: GSN Address */
+		  "0004" /* length */
+		  "abcdef00"
+		"85"	/* 133: GSN Address (second entry) */
+		  "0004" /* length */
+		  "fedcba00"
+		"86"	/* 134: MS International PSTN/ISDN Number (MSISDN) */
+		  "0007" /* length */
+		  "916407123254f6" /* 1946702123456(f) */
+		"87"	/* 135: Quality of Service (QoS) Profile */
+		  "0004" /* length */
+		  "00"	/* priority */
+		  "0b921f" /* QoS profile data */
+		;
+
+	const char *gtp_req_to_ggsn =
+		"32" "10" "0067" "00000000"
+		"6d31"	/* mapped seq ("abcd") */
+		"00" "00" "02" "42000121436587f9" "0e60" "0f01"
+		"10" "00000001" /* mapped TEI Data I ("123") */
+		"11" "00000001" /* mapped TEI Control ("321") */
+		"1400" "1a" "0800" "80" "0002" "f121" "83"
+		"0008" "696e7465726e6574" "84" "0015"
+		"80c0231101010011036d69670868656d6d656c6967" "85" "0004"
+		"7f000201" /* replaced with gtphub's address ggsn ctrl */
+		"85" "0004"
+		"7f000202" /* replaced with gtphub's address ggsn user */
+		"86" "0007" "916407123254f6"
+		"87" "0004" "00" "0b921f"
+		;
+
+	const char *gtp_resp_from_ggsn =
+		"32"
+		"11"	/* Create PDP Context Response */
+		"004e"	/* length = 78 + 8 */
+		"00000001" /* destination TEI (sent in req above) */
+		"6d31"	/* mapped seq */
+		"00" "00"
+		/* IEs */
+		"01"	/* 1: Cause */
+		  "80"	/* value = 0b10000000 = response, no rejection. */
+		"08"	/* 8: Reordering Required */
+		  "00"	/* not required. */
+		"0e" "01" /* 14: Recovery = 1 */
+		"10"	/* 16: TEI Data I */
+		  "00000567"
+		"11"	/* 17: TEI Control */
+		  "00000765"
+		"7f"	/* 127: Charging ID */
+		  "00000001"
+		"80"	/* 128: End User Address */
+		  "0006" /* length = 6 */
+		  "f121" /* spare 0xf0, PDP organization 1, PDP type number 0x21 = 33 */
+		  "7f000002"
+		"84"	/* 132: Protocol Configuration Options */
+		  "0014" /* len = 20 */
+		  "8080211002000010810608080808830600000000"
+		"85"	/* 133: GSN Address (Ctrl) */
+		  "0004" /* length */
+		  "7f000002"
+		"85"	/* 133: GSN Address (User) */
+		  "0004" /* length */
+		  "7f000002"
+		"87"	/* 135: Quality of Service (QoS) Profile */
+		  "0004" /* length */
+		  "00"	/* priority */
+		  "0b921f" /* QoS profile data */
+		;
+
+	const char *gtp_resp_to_sgsn =
+		"32" "11" "004e"
+		"00000321" /* unmapped TEI ("001") */
+		"abcd" /* unmapped seq ("6d31") */
+		"00" "00" "01" "80" "08" "00" "0e" "01"
+		"10" "00000002" /* mapped TEI from GGSN ("567") */
+		"11" "00000002" /* mapped TEI from GGSN ("765") */
+		"7f" "00000001" "80" "0006" "f121" "7f000002" "84" "0014"
+		"8080211002000010810608080808830600000000"
+		"85" "0004"
+		  "7f000101" /* gtphub's address towards SGSNs (Ctrl) */
+		"85" "0004"
+		  "7f000102" /* gtphub's address towards SGSNs (User) */
+		"87" "0004" "00" "0b921f"
+		;
+
+	/* Set the GGSN address that gtphub is forced to resolve to. */
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&resolved_ggsn_addr,
+					   "192.168.43.34", 434)
+		    == 0);
+
+	struct osmo_sockaddr orig_sgsn_addr;
+	OSMO_ASSERT(osmo_sockaddr_init(&orig_sgsn_addr,
+				       AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				       "192.168.42.23", 423) == 0);
+	struct osmo_fd *ggsn_ofd = NULL;
+	struct osmo_sockaddr ggsn_addr;
+	int send;
+	send = gtphub_from_sgsns_handle_buf(hub, GTPH_PLANE_CTRL, &orig_sgsn_addr,
+					    buf, msg(gtp_req_from_sgsn), now,
+					    &ggsn_ofd, &ggsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(same_addr(&ggsn_addr, &resolved_ggsn_addr));
+	OSMO_ASSERT(msg_is(gtp_req_to_ggsn));
+
+	struct osmo_fd *sgsn_ofd;
+	struct osmo_sockaddr sgsn_addr;
+	send = gtphub_from_ggsns_handle_buf(hub, GTPH_PLANE_CTRL, &ggsn_addr,
+					    buf, msg(gtp_resp_from_ggsn), now,
+					    &sgsn_ofd, &sgsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(same_addr(&sgsn_addr, &orig_sgsn_addr));
+	OSMO_ASSERT(msg_is(gtp_resp_to_sgsn));
+
+	struct gtphub_peer_port *ggsn_port =
+		gtphub_port_find_sa(&hub->to_ggsns[GTPH_PLANE_CTRL],
+				    &resolved_ggsn_addr);
+	OSMO_ASSERT(ggsn_port);
+	struct gtphub_peer *ggsn = ggsn_port->peer_addr->peer;
+	/* now == 345; now + 30 == 375.
+	 * seq mapping from above:
+	 *   0xabcd == 43981 (sent in the packet)
+	 *   0x6d31 == 27953 (harcoded seq mapping start val) */
+	OSMO_ASSERT(nr_map_is(&ggsn->seq_map, "(43981->27953@375), "));
+
+	/* now == 345; now + (6 * 60 * 60) == 21600 + 345 == 21945.
+	 * 0x00000321 == 801 (TEI from SGSN Ctrl)
+	 * 0x00000123 == 291 (TEI from SGSN User)
+	 * 0x00000765 == 1893 (TEI from GGSN Ctrl)
+	 * 0x00000567 == 1383 (TEI from GGSN User)
+	 * Mapped TEIs should be 1 and 2. */
+	OSMO_ASSERT(nr_map_is(&hub->tei_map[GTPH_PLANE_CTRL], "(801->1@21945), (1893->2@21945), "));
+	OSMO_ASSERT(nr_map_is(&hub->tei_map[GTPH_PLANE_USER], "(291->1@21945), (1383->2@21945), "));
+
+	gtphub_gc(hub, now + EXPIRE_ALL);
+}
+
+static struct log_info_cat gtphub_categories[] = {
+	[DGTPHUB] = {
+		.name = "DGTPHUB",
+		.description = "GTP Hub",
+		.color = "\033[1;33m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+static struct log_info info = {
+	.cat = gtphub_categories,
+	.num_cat = ARRAY_SIZE(gtphub_categories),
+};
+
+int main(int argc, char **argv)
+{
+	osmo_init_logging(&info);
+	osmo_gtphub_ctx = talloc_named_const(NULL, 0, "osmo_gtphub");
+
+	test_nr_map_basic();
+	test_expiry();
+	test_echo();
+	test_create_pdp_ctx();
+	printf("Done\n");
+
+	talloc_report_full(osmo_gtphub_ctx, stderr);
+	OSMO_ASSERT(talloc_total_blocks(osmo_gtphub_ctx) == 1);
+	return 0;
+}
+
diff --git a/openbsc/tests/gtphub/gtphub_test.ok b/openbsc/tests/gtphub/gtphub_test.ok
new file mode 100644
index 0000000..7be13fe
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_test.ok
@@ -0,0 +1,3 @@
+Wrap: returning GGSN addr: 192.168.43.34 port 434
+Wrap: returning GGSN addr: 192.168.43.34 port 434
+Done
diff --git a/openbsc/tests/testsuite.at b/openbsc/tests/testsuite.at
index 78aa47e..6a1c77f 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -110,3 +110,10 @@
 cat $abs_srcdir/oap/oap_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/oap/oap_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([gtphub])
+AT_KEYWORDS([gtphub])
+AT_CHECK([test "$enable_gtphub_test" != no || exit 77])
+cat $abs_srcdir/gtphub/gtphub_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/gtphub/gtphub_test], [], [expout], [ignore])
+AT_CLEANUP