pimd: MSDP SA forwarding

* If the MSDP peer receives the SA from a non-RPF peer towards the
originating RP, it will drop the message.
* SA messages are forwarded away from the RP address only.
* SA messages are not forwarded within the mesh group.
* Preventing the MSDP connection from being dropped due to RPF check
failure (RFC3618, section 13 "MSDP Error Handling")

Signed-off-by: Adriano Marto Reis <adrianomarto@gmail.com>
Signed-off-by: Adriano Reis <areis@barrukka.local>

4 files changed, 58 insertions, 13 deletions

diff --git a/pimd/pim_cmd.c b/pimd/pim_cmd.c
index db3f0b8b23..6256774464 100644
--- a/pimd/pim_cmd.c
+++ b/pimd/pim_cmd.c
@@ -9694,7 +9694,7 @@ static int ip_msdp_peer_cmd_worker(struct pim_instance *pim, struct vty *vty,
 	return ret;
 }
 
-DEFUN_HIDDEN (ip_msdp_peer,
+DEFUN (ip_msdp_peer,
        ip_msdp_peer_cmd,
        "ip msdp peer A.B.C.D source A.B.C.D",
        IP_STR
@@ -9735,7 +9735,7 @@ static int ip_no_msdp_peer_cmd_worker(struct pim_instance *pim, struct vty *vty,
 	return result ? CMD_WARNING_CONFIG_FAILED : CMD_SUCCESS;
 }
 
-DEFUN_HIDDEN (no_ip_msdp_peer,
+DEFUN (no_ip_msdp_peer,
        no_ip_msdp_peer_cmd,
        "no ip msdp peer A.B.C.D",
        NO_STR
diff --git a/pimd/pim_msdp.c b/pimd/pim_msdp.c
index b42092a464..7336cdfef8 100644
--- a/pimd/pim_msdp.c
+++ b/pimd/pim_msdp.c
@@ -423,6 +423,7 @@ void pim_msdp_sa_ref(struct pim_instance *pim, struct pim_msdp_peer *mp,
 					   sa->sg_str);
 			}
 			/* send an immediate SA update to peers */
+			sa->rp = pim->msdp.originator_id;
 			pim_msdp_pkt_sa_tx_one(sa);
 		}
 		sa->flags &= ~PIM_MSDP_SAF_STALE;
@@ -721,10 +722,18 @@ static int pim_msdp_sa_comp(const void *p1, const void *p2)
 /* XXX: this can use a bit of refining and extensions */
 bool pim_msdp_peer_rpf_check(struct pim_msdp_peer *mp, struct in_addr rp)
 {
+	struct pim_nexthop nexthop;
+
 	if (mp->peer.s_addr == rp.s_addr) {
 		return true;
 	}
 
+	/* check if the MSDP peer is the nexthop for the RP */
+	if (pim_nexthop_lookup(mp->pim, &nexthop, rp, 0)
+	    && nexthop.mrib_nexthop_addr.u.prefix4.s_addr == mp->peer.s_addr) {
+		return true;
+	}
+
 	return false;
 }
 
diff --git a/pimd/pim_msdp_packet.c b/pimd/pim_msdp_packet.c
index 39e39b9557..4aaf0f53d1 100644
--- a/pimd/pim_msdp_packet.c
+++ b/pimd/pim_msdp_packet.c
@@ -348,7 +348,8 @@ static void pim_msdp_pkt_sa_push(struct pim_instance *pim,
 	}
 }
 
-static int pim_msdp_pkt_sa_fill_hdr(struct pim_instance *pim, int local_cnt)
+static int pim_msdp_pkt_sa_fill_hdr(struct pim_instance *pim, int local_cnt,
+				    struct in_addr rp)
 {
 	int curr_tlv_ecnt;
 
@@ -361,7 +362,7 @@ static int pim_msdp_pkt_sa_fill_hdr(struct pim_instance *pim, int local_cnt)
 	stream_putw(pim->msdp.work_obuf,
 		    PIM_MSDP_SA_ENTRY_CNT2SIZE(curr_tlv_ecnt));
 	stream_putc(pim->msdp.work_obuf, curr_tlv_ecnt);
-	stream_put_ipv4(pim->msdp.work_obuf, pim->msdp.originator_id.s_addr);
+	stream_put_ipv4(pim->msdp.work_obuf, rp.s_addr);
 
 	return local_cnt;
 }
@@ -387,7 +388,8 @@ static void pim_msdp_pkt_sa_gen(struct pim_instance *pim,
 		zlog_debug("  sa gen  %d", local_cnt);
 	}
 
-	local_cnt = pim_msdp_pkt_sa_fill_hdr(pim, local_cnt);
+	local_cnt = pim_msdp_pkt_sa_fill_hdr(pim, local_cnt,
+					     pim->msdp.originator_id);
 
 	for (ALL_LIST_ELEMENTS_RO(pim->msdp.sa_list, sanode, sa)) {
 		if (!(sa->flags & PIM_MSDP_SAF_LOCAL)) {
@@ -408,7 +410,8 @@ static void pim_msdp_pkt_sa_gen(struct pim_instance *pim,
 				zlog_debug("  sa gen for remainder %d",
 					   local_cnt);
 			}
-			local_cnt = pim_msdp_pkt_sa_fill_hdr(pim, local_cnt);
+			local_cnt = pim_msdp_pkt_sa_fill_hdr(
+				pim, local_cnt, pim->msdp.originator_id);
 		}
 	}
 
@@ -441,7 +444,7 @@ void pim_msdp_pkt_sa_tx(struct pim_instance *pim)
 
 void pim_msdp_pkt_sa_tx_one(struct pim_msdp_sa *sa)
 {
-	pim_msdp_pkt_sa_fill_hdr(sa->pim, 1 /* cnt */);
+	pim_msdp_pkt_sa_fill_hdr(sa->pim, 1 /* cnt */, sa->rp);
 	pim_msdp_pkt_sa_fill_one(sa);
 	pim_msdp_pkt_sa_push(sa->pim, NULL);
 	pim_msdp_pkt_sa_tx_done(sa->pim);
@@ -454,6 +457,24 @@ void pim_msdp_pkt_sa_tx_to_one_peer(struct pim_msdp_peer *mp)
 	pim_msdp_pkt_sa_tx_done(mp->pim);
 }
 
+void pim_msdp_pkt_sa_tx_one_to_one_peer(struct pim_msdp_peer *mp,
+					struct in_addr rp, struct prefix_sg sg)
+{
+	struct pim_msdp_sa sa;
+
+	/* Fills the SA header. */
+	pim_msdp_pkt_sa_fill_hdr(mp->pim, 1, rp);
+
+	/* Fills the message contents. */
+	sa.pim = mp->pim;
+	sa.sg = sg;
+	pim_msdp_pkt_sa_fill_one(&sa);
+
+	/* Pushes the message. */
+	pim_msdp_pkt_sa_push(sa.pim, mp);
+	pim_msdp_pkt_sa_tx_done(sa.pim);
+}
+
 static void pim_msdp_pkt_rxed_with_fatal_error(struct pim_msdp_peer *mp)
 {
 	pim_msdp_peer_reset_tcp_conn(mp, "invalid-pkt-rx");
@@ -473,6 +494,8 @@ static void pim_msdp_pkt_sa_rx_one(struct pim_msdp_peer *mp, struct in_addr rp)
 {
 	int prefix_len;
 	struct prefix_sg sg;
+	struct listnode *peer_node;
+	struct pim_msdp_peer *peer;
 
 	/* just throw away the three reserved bytes */
 	stream_get3(mp->ibuf);
@@ -493,6 +516,18 @@ static void pim_msdp_pkt_sa_rx_one(struct pim_msdp_peer *mp, struct in_addr rp)
 		zlog_debug("  sg %s", pim_str_sg_dump(&sg));
 	}
 	pim_msdp_sa_ref(mp->pim, mp, &sg, rp);
+
+	/* Forwards the SA to the peers that are not in the RPF to the RP nor in
+	 * the same mesh group as the peer from which we received the message.
+	 * If the message group is not set, i.e. "default", then we assume that
+	 * the message must be forwarded.*/
+	for (ALL_LIST_ELEMENTS_RO(mp->pim->msdp.peer_list, peer_node, peer)) {
+		if (!pim_msdp_peer_rpf_check(peer, rp)
+		    && (strcmp(mp->mesh_group_name, peer->mesh_group_name)
+			|| !strcmp(mp->mesh_group_name, "default"))) {
+			pim_msdp_pkt_sa_tx_one_to_one_peer(peer, rp, sg);
+		}
+	}
 }
 
 static void pim_msdp_pkt_sa_rx(struct pim_msdp_peer *mp, int len)
@@ -510,10 +545,9 @@ static void pim_msdp_pkt_sa_rx(struct pim_msdp_peer *mp, int len)
 
 	entry_cnt = stream_getc(mp->ibuf);
 	/* some vendors include the actual multicast data in the tlv (at the
-	 * end).
-	 * we will ignore such data. in the future we may consider pushing it
-	 * down
-	 * the RPT */
+	 * end). we will ignore such data. in the future we may consider pushing
+	 * it down the RPT
+	 */
 	if (len < PIM_MSDP_SA_ENTRY_CNT2SIZE(entry_cnt)) {
 		pim_msdp_pkt_rxed_with_fatal_error(mp);
 		return;
@@ -526,6 +560,8 @@ static void pim_msdp_pkt_sa_rx(struct pim_msdp_peer *mp, int len)
 		zlog_debug("  entry_cnt %d rp %s", entry_cnt, rp_str);
 	}
 
+	pim_msdp_peer_pkt_rxed(mp);
+
 	if (!pim_msdp_peer_rpf_check(mp, rp)) {
 		/* if peer-RPF check fails don't process the packet any further
 		 */
@@ -535,8 +571,6 @@ static void pim_msdp_pkt_sa_rx(struct pim_msdp_peer *mp, int len)
 		return;
 	}
 
-	pim_msdp_peer_pkt_rxed(mp);
-
 	/* update SA cache */
 	for (i = 0; i < entry_cnt; ++i) {
 		pim_msdp_pkt_sa_rx_one(mp, rp);
diff --git a/pimd/pim_msdp_packet.h b/pimd/pim_msdp_packet.h
index d922fa50df..f5af8d1140 100644
--- a/pimd/pim_msdp_packet.h
+++ b/pimd/pim_msdp_packet.h
@@ -67,5 +67,7 @@ int pim_msdp_read(struct thread *thread);
 void pim_msdp_pkt_sa_tx(struct pim_instance *pim);
 void pim_msdp_pkt_sa_tx_one(struct pim_msdp_sa *sa);
 void pim_msdp_pkt_sa_tx_to_one_peer(struct pim_msdp_peer *mp);
+void pim_msdp_pkt_sa_tx_one_to_one_peer(struct pim_msdp_peer *mp,
+					struct in_addr rp, struct prefix_sg sg);
 
 #endif