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;
+}