diff --git a/openbsc/include/openbsc/gb_proxy.h b/openbsc/include/openbsc/gb_proxy.h
index 18ed81f..9610ca6 100644
--- a/openbsc/include/openbsc/gb_proxy.h
+++ b/openbsc/include/openbsc/gb_proxy.h
@@ -13,6 +13,7 @@
 	GBPROX_PATCH_LLC_ATTACH_REQ,	/*!< BSSGP and Attach Request */
 	GBPROX_PATCH_LLC_ATTACH,	/*!< BSSGP and Attach Request/Response */
 	GBPROX_PATCH_LLC_GMM,		/*!< BSSGP and all GMM msgs */
+	GBPROX_PATCH_LLC_GSM,		/*!< BSSGP and all GMM and GSM msgs */
 	GBPROX_PATCH_LLC,		/*!< BSSGP and all supported LLC msgs */
 };
 
@@ -26,6 +27,8 @@
 	/* force mcc/mnc */
 	int core_mnc;
 	int core_mcc;
+	uint8_t* core_apn;
+	size_t core_apn_size;
 	enum gbproxy_patch_mode patch_mode;
 };
 
@@ -54,4 +57,7 @@
 int gbprox_dump_global(FILE *stream, int indent);
 int gbprox_dump_peers(FILE *stream, int indent);
 void gbprox_reset();
+
+char *gbprox_apn_to_str(char *str, const uint8_t *apn_enc, size_t max_chars);
+int gbprox_str_to_apn(uint8_t *apn_enc, const char *str, size_t max_chars);
 #endif
diff --git a/openbsc/src/gprs/gb_proxy.c b/openbsc/src/gprs/gb_proxy.c
index 6daf450..5d508e7 100644
--- a/openbsc/src/gprs/gb_proxy.c
+++ b/openbsc/src/gprs/gb_proxy.c
@@ -61,6 +61,7 @@
 	GBPROX_GLOB_CTR_OTHER_ERR,
 	GBPROX_GLOB_CTR_RAID_PATCHED_BSS,
 	GBPROX_GLOB_CTR_RAID_PATCHED_SGSN,
+	GBPROX_GLOB_CTR_APN_PATCHED,
 	GBPROX_GLOB_CTR_PATCH_CRYPT_ERR,
 	GBPROX_GLOB_CTR_PATCH_ERR,
 };
@@ -79,6 +80,7 @@
 	{ "error",          "Other error                     " },
 	{ "raid-mod.bss",   "RAID patched              (BSS )" },
 	{ "raid-mod.sgsn",  "RAID patched              (SGSN)" },
+	{ "apn-mod.sgsn",   "APN patched                     " },
 	{ "mod-crypt-err",  "Patch error: encrypted          " },
 	{ "mod-err",        "Patch error: other              " },
 };
@@ -277,6 +279,89 @@
 	msgb_pull(msg, strip_len);
 }
 
+/* TODO: Move this to libosmocore/msgb.c */
+static int msgb_resize_area(struct msgb *msg, uint8_t *area,
+			    size_t old_size, size_t new_size)
+{
+	int rc;
+	uint8_t *rest = area + old_size;
+	int rest_len = msg->len - old_size - (area - msg->data);
+	int delta_size = (int)new_size - (int)old_size;
+
+	if (delta_size == 0)
+		return 0;
+
+	if (delta_size > 0) {
+		rc = msgb_trim(msg, msg->len + delta_size);
+		if (rc < 0)
+			return rc;
+	}
+
+	memmove(area + new_size, area + old_size, rest_len);
+
+	if (msg->l1h >= rest)
+		msg->l1h += delta_size;
+	if (msg->l2h >= rest)
+		msg->l2h += delta_size;
+	if (msg->l3h >= rest)
+		msg->l3h += delta_size;
+	if (msg->l4h >= rest)
+		msg->l4h += delta_size;
+
+	if (delta_size < 0)
+		msgb_trim(msg, msg->len + delta_size);
+
+	return 0;
+}
+
+/* TODO: Move these conversion functions to a utils file. */
+char * gbprox_apn_to_str(char *out_str, const uint8_t *apn_enc, size_t rest_chars)
+{
+	char *str = out_str;
+
+	while (rest_chars > 0 && apn_enc[0]) {
+		size_t label_size = apn_enc[0];
+		if (label_size + 1 > rest_chars)
+			return NULL;
+
+		memmove(str, apn_enc + 1, label_size);
+		str += label_size;
+		rest_chars -= label_size + 1;
+		apn_enc += label_size + 1;
+
+		if (rest_chars)
+			*(str++) = '.';
+	}
+	str[0] = '\0';
+
+	return out_str;
+}
+
+int gbprox_str_to_apn(uint8_t *apn_enc, const char *str, size_t max_chars)
+{
+	uint8_t *last_len_field = apn_enc;
+	int len = 1;
+	apn_enc += 1;
+
+	while (str[0]) {
+		if (str[0] == '.') {
+			*last_len_field = (apn_enc - last_len_field) - 1;
+			last_len_field = apn_enc;
+		} else {
+			*apn_enc = str[0];
+		}
+		apn_enc += 1;
+		str += 1;
+		len += 1;
+		if (len > max_chars)
+			return -1;
+	}
+
+	*last_len_field = (apn_enc - last_len_field) - 1;
+
+	return len;
+}
+
 /* check whether patching is enabled at this level */
 static int patching_is_enabled(enum gbproxy_patch_mode need_at_least)
 {
@@ -364,6 +449,56 @@
 	}
 }
 
+static void gbprox_patch_apn_ie(struct msgb *msg,
+				uint8_t *apn_ie, size_t apn_ie_len,
+				size_t *new_apn_ie_len, const char *log_text)
+{
+	struct apn_ie_hdr {
+		uint8_t iei;
+		uint8_t apn_len;
+		uint8_t apn[0];
+	} *hdr = (void *)apn_ie;
+
+	size_t apn_len = hdr->apn_len;
+	uint8_t *apn = hdr->apn;
+
+	OSMO_ASSERT(apn_ie_len == apn_len + sizeof(struct apn_ie_hdr));
+	OSMO_ASSERT(apn_ie_len > 2 && apn_ie_len <= 102);
+
+	if (gbcfg.core_apn_size == 0) {
+		char str1[110];
+		/* Remove the IE */
+		LOGP(DGPRS, LOGL_DEBUG,
+		     "Patching %s to SGSN: Removing APN '%s'\n",
+		     log_text,
+		     gbprox_apn_to_str(str1, apn, apn_len));
+
+		*new_apn_ie_len = 0;
+		msgb_resize_area(msg, apn_ie, apn_ie_len, 0);
+	} else {
+		/* Resize the IE */
+		char str1[110];
+		char str2[110];
+
+		OSMO_ASSERT(gbcfg.core_apn_size <= 100);
+
+		LOGP(DGPRS, LOGL_DEBUG,
+		     "Patching %s to SGSN: "
+		     "Replacing APN '%s' -> '%s'\n",
+		     log_text,
+		     gbprox_apn_to_str(str1, apn, apn_len),
+		     gbprox_apn_to_str(str2, gbcfg.core_apn,
+				       gbcfg.core_apn_size));
+
+		*new_apn_ie_len = gbcfg.core_apn_size + 2;
+		msgb_resize_area(msg, apn, apn_len, gbcfg.core_apn_size);
+		memcpy(apn, gbcfg.core_apn, gbcfg.core_apn_size);
+		hdr->apn_len = gbcfg.core_apn_size;
+	}
+
+	rate_ctr_inc(&get_global_ctrg()->ctr[GBPROX_GLOB_CTR_APN_PATCHED]);
+}
+
 static int gbprox_patch_gmm_attach_req(struct msgb *msg,
 				       uint8_t *data, size_t data_len,
 				       struct gbprox_patch_state *state,
@@ -480,6 +615,60 @@
 	return 1;
 }
 
+static int gbprox_patch_gsm_act_pdp_req(struct msgb *msg,
+					uint8_t *data, size_t data_len,
+					struct gbprox_patch_state *state,
+					int to_bss, int *len_change)
+{
+	size_t new_len, old_len;
+
+	/* Check minimum length, always contains length field of
+	 * Requested QoS */
+	if (data_len < 9)
+		return 0;
+
+	/* Skip Requested NSAPI */
+	/* Skip Requested LLC SAPI */
+	data_len -= 2;
+	data += 2;
+
+	/* Skip Requested QoS (support 04.08 and 24.008) */
+	if (data[0] < 4 || data[0] > 14 ||
+	    data_len - (data[0] + 1) < 0)
+		/* invalid */
+		return 0;
+	data_len -= data[0] + 1;
+	data += data[0] + 1;
+
+	/* Skip Requested PDP address */
+	if (data_len < 1 ||
+	    data[0] < 2 || data[0] > 18 ||
+	    data_len - (data[0] + 1) < 0)
+		/* invalid */
+		return 0;
+	data_len -= data[0] + 1;
+	data += data[0] + 1;
+
+	/* Access point name */
+	if (data_len < 2 || data[0] != GSM48_IE_GSM_APN)
+		return 0;
+
+	if (data[1] < 1 || data[1] > 100 ||
+	    data_len - (data[1] + 2) < 0)
+		/* invalid */
+		return 0;
+
+	old_len = data[1] + 2;
+
+	gbprox_patch_apn_ie(msg, data, old_len, &new_len, "LLC/ACT_PDP_REQ");
+
+	*len_change += (int)new_len - (int)old_len;
+	data_len -= old_len;
+	data += new_len;
+
+	return 1;
+}
+
 static int gbprox_patch_dtap(struct msgb *msg, uint8_t *data, size_t data_len,
 			     struct gbprox_patch_state *state, int to_bss,
 			     int *len_change)
@@ -529,6 +718,13 @@
 		return gbprox_patch_gmm_ptmsi_reall_cmd(msg, data, data_len,
 							state, to_bss, len_change);
 
+	case GSM48_MT_GSM_ACT_PDP_REQ:
+		if (!patching_is_enabled(GBPROX_PATCH_LLC_GSM))
+			break;
+		if (gbcfg.core_apn == NULL)
+			break;
+		return gbprox_patch_gsm_act_pdp_req(msg, data, data_len,
+						    state, to_bss, len_change);
 	default:
 		break;
 	};
@@ -640,7 +836,7 @@
 	uint8_t *data;
 	size_t data_len;
 
-	if (!gbcfg.core_mcc && !gbcfg.core_mnc)
+	if (!gbcfg.core_mcc && !gbcfg.core_mnc && !gbcfg.core_apn)
 		return;
 
 	bgph = (struct bssgp_normal_hdr *) msgb_bssgph(msg);
diff --git a/openbsc/src/gprs/gb_proxy_vty.c b/openbsc/src/gprs/gb_proxy_vty.c
index 4803347..6d24165 100644
--- a/openbsc/src/gprs/gb_proxy_vty.c
+++ b/openbsc/src/gprs/gb_proxy_vty.c
@@ -21,6 +21,7 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <string.h>
 
 #include <osmocom/core/talloc.h>
 
@@ -50,6 +51,7 @@
 	{GBPROX_PATCH_LLC_ATTACH_REQ, "llc-attach-req"},
 	{GBPROX_PATCH_LLC_ATTACH, "llc-attach"},
 	{GBPROX_PATCH_LLC_GMM, "llc-gmm"},
+	{GBPROX_PATCH_LLC_GSM, "llc-gsm"},
 	{GBPROX_PATCH_LLC, "llc"},
 	{0, NULL}
 };
@@ -67,6 +69,18 @@
 	if (g_cfg->core_mnc > 0)
 		vty_out(vty, " core-mobile-network-code %d%s",
 			g_cfg->core_mnc, VTY_NEWLINE);
+	if (g_cfg->core_apn != NULL) {
+	       if (g_cfg->core_apn_size > 0) {
+		       char str[500] = {0};
+		       vty_out(vty, " core-access-point-name %s%s",
+			       gbprox_apn_to_str(str, g_cfg->core_apn,
+						 g_cfg->core_apn_size),
+			       VTY_NEWLINE);
+	       } else {
+		       vty_out(vty, " core-access-point-name%s",
+			       VTY_NEWLINE);
+	       }
+	}
 
 	if (g_cfg->patch_mode != GBPROX_PATCH_DEFAULT)
 		vty_out(vty, " patch-mode %s%s",
@@ -138,15 +152,62 @@
 	return CMD_SUCCESS;
 }
 
+#define GBPROXY_CORE_APN_STR "Use this access point name (APN) for the backbone\n"
+
+DEFUN(cfg_gbproxy_core_apn_remove,
+      cfg_gbproxy_core_apn_remove_cmd,
+      "core-access-point-name",
+      GBPROXY_CORE_APN_STR)
+{
+	talloc_free(g_cfg->core_apn);
+	/* TODO: replace NULL */
+	g_cfg->core_apn = talloc_zero_size(NULL, 2);
+	g_cfg->core_apn_size = 0;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gbproxy_core_apn,
+      cfg_gbproxy_core_apn_cmd,
+      "core-access-point-name APN",
+      GBPROXY_CORE_APN_STR "Replacement APN\n")
+{
+	int apn_len = strlen(argv[0]) + 1;
+
+	if (apn_len > 100) {
+		vty_out(vty, "APN string too long (max 99 chars)%s",
+			VTY_NEWLINE);
+		return CMD_WARNING;
+	}
+
+	/* TODO: replace NULL */
+	g_cfg->core_apn = talloc_realloc_size(NULL, g_cfg->core_apn, apn_len);
+	g_cfg->core_apn_size = gbprox_str_to_apn(g_cfg->core_apn, argv[0], apn_len);
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gbproxy_no_core_apn,
+      cfg_gbproxy_no_core_apn_cmd,
+      "no core-access-point-name",
+      NO_STR GBPROXY_CORE_APN_STR)
+{
+	talloc_free(g_cfg->core_apn);
+	g_cfg->core_apn = NULL;
+	g_cfg->core_apn_size = 0;
+	return CMD_SUCCESS;
+}
+
 DEFUN(cfg_gbproxy_patch_mode,
       cfg_gbproxy_patch_mode_cmd,
-      "patch-mode (default|bssgp|llc-attach-req|llc-attach|llc)",
+      "patch-mode (default|bssgp|llc-attach-req|llc-attach|llc-gmm|llc-gsm|llc)",
       "Set patch mode\n"
-      "Use build-in default (at least llc-attach-req)\n"
+      "Use build-in default (best effort, try to patch everything)\n"
       "Only patch BSSGP headers\n"
       "Patch BSSGP headers and LLC Attach Request messages\n"
       "Patch BSSGP headers and LLC Attach Request/Accept messages\n"
-      "Patch BSSGP headers and all supported GMM LLC messages\n"
+      "Patch BSSGP headers and LLC GMM messages\n"
+      "Patch BSSGP headers, LLC GMM, and LLC GSM messages\n"
+      "Patch BSSGP headers and all supported LLC messages\n"
       )
 {
 	int val = get_string_value(patch_modes, argv[0]);
@@ -170,8 +231,11 @@
 	install_element(GBPROXY_NODE, &cfg_nsip_sgsn_nsei_cmd);
 	install_element(GBPROXY_NODE, &cfg_gbproxy_core_mcc_cmd);
 	install_element(GBPROXY_NODE, &cfg_gbproxy_core_mnc_cmd);
+	install_element(GBPROXY_NODE, &cfg_gbproxy_core_apn_remove_cmd);
+	install_element(GBPROXY_NODE, &cfg_gbproxy_core_apn_cmd);
 	install_element(GBPROXY_NODE, &cfg_gbproxy_no_core_mcc_cmd);
 	install_element(GBPROXY_NODE, &cfg_gbproxy_no_core_mnc_cmd);
+	install_element(GBPROXY_NODE, &cfg_gbproxy_no_core_apn_cmd);
 	install_element(GBPROXY_NODE, &cfg_gbproxy_patch_mode_cmd);
 
 	return 0;
diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index e93c354..33b0ac5 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -812,6 +812,8 @@
 	gbcfg.nsip_sgsn_nsei = SGSN_NSEI;
 	gbcfg.core_mcc = 123;
 	gbcfg.core_mnc = 456;
+	gbcfg.core_apn = talloc_zero_size(NULL, 100);
+	gbcfg.core_apn_size = gbprox_str_to_apn(gbcfg.core_apn, "foo.bar", 100);
 
 	configure_sgsn_peer(&sgsn_peer);
 	configure_bss_peers(bss_peer, ARRAY_SIZE(bss_peer));
@@ -856,7 +858,8 @@
 			 &bss_peer[0], 0x1002,
 			 bssgp_act_pdp_ctx_req, sizeof(bssgp_act_pdp_ctx_req));
 
-	/* TODO: Re-configure to test APN IE removal */
+	gbcfg.core_apn[0] = 0;
+	gbcfg.core_apn_size = 0;
 
 	/* Remove APN */
 	send_ns_unitdata(nsi, "ACT PDP CTX REQ (REMOVE APN)",
diff --git a/openbsc/tests/gbproxy/gbproxy_test.ok b/openbsc/tests/gbproxy/gbproxy_test.ok
index 64ed996..e73b254 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.ok
+++ b/openbsc/tests/gbproxy/gbproxy_test.ok
@@ -1617,11 +1617,11 @@
 CALLBACK, event 0, msg length 76, bvci 0x1002
 00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 11 22 33 40 50 60 75 30 00 80 0e 00 35 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 03 02 61 62 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 5a ff 02 
 
-NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 76 (gprs_ns_sendmsg)
-MESSAGE to SGSN at 0x05060708:32000, msg length 80
-00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 75 30 00 80 0e 00 35 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 03 02 61 62 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 5a ff 02 
+NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 81 (gprs_ns_sendmsg)
+MESSAGE to SGSN at 0x05060708:32000, msg length 85
+00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 75 30 00 80 0e 00 3a 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 08 03 66 6f 6f 03 62 61 72 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 24 9d 75 
 
-result (ACT PDP CTX REQ (REPLACE APN)) = 80
+result (ACT PDP CTX REQ (REPLACE APN)) = 85
 
 PROCESSING ACT PDP CTX REQ (REMOVE APN) from 0x01020304:1111
 00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 11 22 33 40 50 60 75 30 00 80 0e 00 35 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 03 02 61 62 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 5a ff 02 
@@ -1629,15 +1629,16 @@
 CALLBACK, event 0, msg length 76, bvci 0x1002
 00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 11 22 33 40 50 60 75 30 00 80 0e 00 35 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 03 02 61 62 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 5a ff 02 
 
-NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 76 (gprs_ns_sendmsg)
-MESSAGE to SGSN at 0x05060708:32000, msg length 80
-00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 75 30 00 80 0e 00 35 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 28 03 02 61 62 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 5a ff 02 
+NS UNITDATA MESSAGE to SGSN, BVCI 0x1002, msg length 71 (gprs_ns_sendmsg)
+MESSAGE to SGSN at 0x05060708:32000, msg length 75
+00 00 10 02 01 ef e2 b7 00 00 00 04 08 88 21 63 54 40 50 60 75 30 00 80 0e 00 30 01 c0 0d 0a 41 05 03 0c 00 00 1f 10 00 00 00 00 00 00 00 00 02 01 21 27 14 80 80 21 10 01 00 00 10 81 06 00 00 00 00 83 06 00 00 00 00 85 fa 60 
 
-result (ACT PDP CTX REQ (REMOVE APN)) = 80
+result (ACT PDP CTX REQ (REMOVE APN)) = 75
 
 Gbproxy global:
     RAID patched              (BSS ): 8
     RAID patched              (SGSN): 3
+    APN patched                     : 2
 Peers:
   NSEI 4096, BVCI 4098, not blocked, RAI 112-332-16464-96
 --- Bad cases ---
@@ -1667,6 +1668,7 @@
     Invalid Routing Area Identifier : 1
     RAID patched              (BSS ): 8
     RAID patched              (SGSN): 4
+    APN patched                     : 2
 Peers:
   NSEI 4096, BVCI 4098, not blocked, RAI 112-332-16464-96
 ===== GbProxy test END