diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index 31009bb..c7d97aa 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -731,9 +731,17 @@
 		case SCCP_MSG_TYPE_IT:
 			con = patch_sccp_src_ref_to_msc(msg, parsed, bsc);
 			if (con) {
-				con_bsc = con->bsc;
-				con_msc = con->msc_con;
-				con_filter = con->con_local;
+				filter = bsc_nat_filter_dt(bsc, msg, con, parsed);
+				if (filter == 0) {
+					con_bsc = con->bsc;
+					con_msc = con->msc_con;
+					con_filter = con->con_local;
+				} else {
+					LOGP(DNAT, LOGL_ERROR, "Should drop the connection.\n");
+					con_bsc = con->bsc;
+					con_msc = con->msc_con;
+					con_filter = con->con_local;
+				}
 			}
 			break;
 		case SCCP_MSG_TYPE_RLC:
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index e81a1e8..7387b51 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -431,6 +431,15 @@
 	}
 }
 
+int bsc_nat_filter_dt(struct bsc_connection *bsc, struct msgb *msg,
+		      struct sccp_connections *con, struct bsc_nat_parsed *parsed)
+{
+	if (con->imsi_checked)
+		return 0;
+
+	return 0;
+}
+
 void bsc_parse_reg(void *ctx, regex_t *reg, char **imsi, int argc, const char **argv)
 {
 	if (*imsi) {