bgpd: add [no]neighbor capability fqdn command

cisco routers are not dealing fairly whith unsupported capabilities.
When a cisco router receive an unsupported capabilities it reset the
negociation without notifying the unmatching capability as described in
RFC2842.
Cisco suggest the use of
neighbor x.x.x.x capability fqdn
to avoid the use of fqdn in open message.

this new command is to remove the use of fqdn capability in the
open message with the peer "x.x.x.x".

Link: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/116189-problemsolution-technology-00.pdf

Signed-off-by: Francois Dumontet <francois.dumontet@6wind.com>

bgpd/bgp_open.c

@@ -1897,8 +1897,9 @@ uint16_t bgp_open_capability(struct stream *s, struct peer *peer,
 		stream_putc(s, CAPABILITY_CODE_DYNAMIC_LEN);
 	}
 
-	/* Hostname capability */
-	if (cmd_hostname_get()) {
+	/* FQDN capability */
+	if (CHECK_FLAG(peer->flags, PEER_FLAG_CAPABILITY_FQDN)
+	    && cmd_hostname_get()) {
 		SET_FLAG(peer->cap, PEER_CAP_HOSTNAME_ADV);
 		stream_putc(s, BGP_OPEN_OPT_CAP);
 		rcapp = stream_get_endp(s); /* Ptr to length placeholder */

bgpd/bgp_vty.c

@@ -5735,6 +5735,30 @@ DEFUN (no_neighbor_dont_capability_negotiate,
 				   PEER_FLAG_DONT_CAPABILITY);
 }
 
+/* neighbor capability fqdn */
+DEFPY (neighbor_capability_fqdn,
+       neighbor_capability_fqdn_cmd,
+       "[no$no] neighbor <A.B.C.D|X:X::X:X|WORD>$neighbor capability fqdn",
+       NO_STR
+       NEIGHBOR_STR
+       NEIGHBOR_ADDR_STR2
+       "Advertise capability to the peer\n"
+       "Advertise fqdn capability to the peer\n")
+{
+	struct peer *peer;
+
+	peer = peer_and_group_lookup_vty(vty, neighbor);
+	if (!peer)
+		return CMD_WARNING_CONFIG_FAILED;
+
+	if (no)
+		return peer_flag_unset_vty(vty, neighbor,
+					  PEER_FLAG_CAPABILITY_FQDN);
+	else
+		return peer_flag_set_vty(vty, neighbor,
+					PEER_FLAG_CAPABILITY_FQDN);
+}
+
 /* neighbor capability extended next hop encoding */
 DEFUN (neighbor_capability_enhe,
        neighbor_capability_enhe_cmd,
@@ -18189,6 +18213,12 @@ static void bgp_config_write_peer_global(struct vty *vty, struct bgp *bgp,
 	if (peergroup_flag_check(peer, PEER_FLAG_DONT_CAPABILITY))
 		vty_out(vty, " neighbor %s dont-capability-negotiate\n", addr);
 
+	/* capability fqdn */
+	if (peergroup_flag_check(peer, PEER_FLAG_CAPABILITY_FQDN))
+		vty_out(vty,
+			" no neighbor %s capability fqdn\n",
+			addr);
+
 	/* override-capability */
 	if (peergroup_flag_check(peer, PEER_FLAG_OVERRIDE_CAPABILITY))
 		vty_out(vty, " neighbor %s override-capability\n", addr);
@@ -20525,6 +20555,9 @@ void bgp_vty_init(void)
 	install_element(BGP_NODE, &neighbor_dont_capability_negotiate_cmd);
 	install_element(BGP_NODE, &no_neighbor_dont_capability_negotiate_cmd);
 
+	/* "neighbor capability fqdn" command. */
+	install_element(BGP_NODE, &neighbor_capability_fqdn_cmd);
+
 	/* "neighbor ebgp-multihop" commands. */
 	install_element(BGP_NODE, &neighbor_ebgp_multihop_cmd);
 	install_element(BGP_NODE, &neighbor_ebgp_multihop_ttl_cmd);

bgpd/bgpd.c

@@ -1535,6 +1535,9 @@ struct peer *peer_new(struct bgp *bgp)
 	if (CHECK_FLAG(bgp->flags, BGP_FLAG_ENFORCE_FIRST_AS))
 		SET_FLAG(peer->flags, PEER_FLAG_ENFORCE_FIRST_AS);
 
+	SET_FLAG(peer->flags_invert, PEER_FLAG_CAPABILITY_FQDN);
+	SET_FLAG(peer->flags, PEER_FLAG_CAPABILITY_FQDN);
+
 	/* Initialize per peer bgp GR FSM */
 	bgp_peer_gr_init(peer);
 
@@ -4571,6 +4574,7 @@ static const struct peer_flag_action peer_flag_action_list[] = {
 	{PEER_FLAG_AIGP, 0, peer_change_none},
 	{PEER_FLAG_GRACEFUL_SHUTDOWN, 0, peer_change_none},
 	{PEER_FLAG_CAPABILITY_SOFT_VERSION, 0, peer_change_none},
+	{PEER_FLAG_CAPABILITY_FQDN, 0, peer_change_reset},
 	{0, 0, 0}};
 
 static const struct peer_flag_action peer_af_flag_action_list[] = {

bgpd/bgpd.h

@@ -1460,6 +1460,7 @@ struct peer {
 #define PEER_FLAG_AIGP (1ULL << 34)
 #define PEER_FLAG_GRACEFUL_SHUTDOWN (1ULL << 35)
 #define PEER_FLAG_CAPABILITY_SOFT_VERSION (1ULL << 36)
+#define PEER_FLAG_CAPABILITY_FQDN (1ULL << 37)  /* fqdn capability */
 
 	/*
 	 *GR-Disabled mode means unset PEER_FLAG_GRACEFUL_RESTART

tests/bgpd/test_peer_attr.c

@@ -282,6 +282,13 @@ static struct test_peer_attr test_peer_attrs[] = {
 		.u.flag = PEER_FLAG_DONT_CAPABILITY,
 		.type = PEER_AT_GLOBAL_FLAG,
 	},
+	{
+		.cmd = "capability fqdn",
+		.u.flag = PEER_FLAG_CAPABILITY_FQDN,
+		.type = PEER_AT_GLOBAL_FLAG,
+		.o.invert_peer = true,
+		.o.invert_group = true,
+	},
 	{
 		.cmd = "local-as",
 		.peer_cmd = "local-as 1",

tests/bgpd/test_peer_attr.py

@@ -15,6 +15,7 @@ TestFlag.okfail("peer\\capability extended-nexthop")
 TestFlag.okfail("peer\\description")
 TestFlag.okfail("peer\\disable-connected-check")
 TestFlag.okfail("peer\\dont-capability-negotiate")
+TestFlag.okfail("peer\\capability fqdn")
 TestFlag.okfail("peer\\local-as")
 TestFlag.okfail("peer\\local-as 1 no-prepend")
 TestFlag.okfail("peer\\local-as 1 no-prepend replace-as")