sgsn: Allow to resolve the IPv4 address of a GGSN through DNS

For real networks we need to check if the requested APN string
is allowed and then resolve the GGSN address through DNS. There
are countries with two or three digit MNCs and one could either
try to keep a list of countries that have two/three digits or
just try both of them. I have opted for the later for the ease
of the implementation.

C-Ares doesn't allow to cancel a request so we will need to
have the MMCTX and the Lookup have different lifetimes. We simply
set ->mmctx to NULL in case the MMCTX dies more early.

The selected and verified apn_str will be copied into the out
parameter. In case no static APN/GGSN config is present and the
dynamic mode is enabled a request will be made.

1 files changed, 15 insertions, 0 deletions

diff --git a/openbsc/src/gprs/sgsn_vty.c b/openbsc/src/gprs/sgsn_vty.c
index b7023adb2..65b5a39e1 100644
--- a/openbsc/src/gprs/sgsn_vty.c
+++ b/openbsc/src/gprs/sgsn_vty.c
@@ -135,12 +135,18 @@ static int config_write_sgsn(struct vty *vty)
 		inet_ntoa(g_cfg->gtp_listenaddr.sin_addr), VTY_NEWLINE);
 
 	llist_for_each_entry(gctx, &sgsn_ggsn_ctxts, list) {
+		if (gctx->id == UINT32_MAX)
+			continue;
+
 		vty_out(vty, " ggsn %u remote-ip %s%s", gctx->id,
 			inet_ntoa(gctx->remote_addr), VTY_NEWLINE);
 		vty_out(vty, " ggsn %u gtp-version %u%s", gctx->id,
 			gctx->gtp_version, VTY_NEWLINE);
 	}
 
+	if (sgsn->cfg.dynamic_lookup)
+		vty_out(vty, " ggsn dynamic%s", VTY_NEWLINE);
+
 	vty_out(vty, " auth-policy %s%s",
 		get_value_string(sgsn_auth_pol_strs, g_cfg->auth_policy),
 		VTY_NEWLINE);
@@ -236,6 +242,14 @@ DEFUN(cfg_ggsn_gtp_version, cfg_ggsn_gtp_version_cmd,
 	return CMD_SUCCESS;
 }
 
+DEFUN(cfg_ggsn_dynamic_lookup, cfg_ggsn_dynamic_lookup_cmd,
+	"ggsn dynamic",
+	GGSN_STR "Enable dynamic GRX based look-up (requires restart)\n")
+{
+	sgsn->cfg.dynamic_lookup = 1;
+	return CMD_SUCCESS;
+}
+
 #define APN_STR	"Configure the information per APN\n"
 #define APN_GW_STR "The APN gateway name optionally prefixed by '*' (wildcard)\n"
 
@@ -878,6 +892,7 @@ int sgsn_vty_init(void)
 	install_element(SGSN_NODE, &cfg_cdr_filename_cmd);
 	install_element(SGSN_NODE, &cfg_no_cdr_filename_cmd);
 	install_element(SGSN_NODE, &cfg_cdr_interval_cmd);
+	install_element(SGSN_NODE, &cfg_ggsn_dynamic_lookup_cmd);
 
 	return 0;
 }