Link state support in BGP.

Configurable fast shutdown of a BGP session when an interface loses link.

doc/bird.sgml

@@ -1691,6 +1691,13 @@ using the following configuration parameters:
 	Specifies a table that is used as an IGP routing table. Default: the
 	same as the table BGP is connected to.
 
+	<tag>check link <M>switch</M></tag>
+	BGP could use hardware link state into consideration.  If enabled,
+	BIRD tracks the link state of the associated interface and when link
+	disappears (e.g. an ethernet cable is unplugged), the BGP session is
+	immediately shut down. Note that this option cannot be used with
+	multihop BGP. Default: disabled.
+
 	<tag>bfd <M>switch</M></tag>
 	BGP could use BFD protocol as an advisory mechanism for neighbor
 	liveness and failure detection. If enabled, BIRD setups a BFD session

proto/bgp/bgp.c

@@ -855,25 +855,43 @@ static void
 bgp_neigh_notify(neighbor *n)
 {
   struct bgp_proto *p = (struct bgp_proto *) n->proto;
+  int ps = p->p.proto_state;
 
-  if (! (n->flags & NEF_STICKY))
+  if (n != p->neigh)
     return;
 
-  if (n->scope > 0)
+  if ((ps == PS_DOWN) || (ps == PS_STOP))
+    return;
+
+  int prepare = (ps == PS_START) && (p->start_state == BSS_PREPARE);
+
+  if (n->scope <= 0)
     {
-      if ((p->p.proto_state == PS_START) && (p->start_state == BSS_PREPARE))
-	{
-	  BGP_TRACE(D_EVENTS, "Neighbor found");
-	  bgp_start_neighbor(p);
+      if (!prepare)
+        {
+	  BGP_TRACE(D_EVENTS, "Neighbor lost");
+	  bgp_store_error(p, NULL, BE_MISC, BEM_NEIGHBOR_LOST);
+	  /* Perhaps also run bgp_update_startup_delay(p)? */
+	  bgp_stop(p, 0);
+	}
+    }
+  else if (p->cf->check_link && !(n->iface->flags & IF_LINK_UP))
+    {
+      if (!prepare)
+        {
+	  BGP_TRACE(D_EVENTS, "Link down");
+	  bgp_store_error(p, NULL, BE_MISC, BEM_LINK_DOWN);
+	  if (ps == PS_UP)
+	    bgp_update_startup_delay(p);
+	  bgp_stop(p, 0);
 	}
     }
   else
     {
-      if ((p->p.proto_state == PS_START) || (p->p.proto_state == PS_UP))
+      if (prepare)
 	{
-	  BGP_TRACE(D_EVENTS, "Neighbor lost");
-	  bgp_store_error(p, NULL, BE_MISC, BEM_NEIGHBOR_LOST);
-	  bgp_stop(p, 0);
+	  BGP_TRACE(D_EVENTS, "Neighbor ready");
+	  bgp_start_neighbor(p);
 	}
     }
 }
@@ -952,8 +970,8 @@ bgp_start_locked(struct object_lock *lock)
       return;
     }
 
-  p->neigh = neigh_find2(&p->p, &cf->remote_ip, cf->iface, NEF_STICKY);
-  if (!p->neigh || (p->neigh->scope == SCOPE_HOST))
+  neighbor *n = neigh_find2(&p->p, &cf->remote_ip, cf->iface, NEF_STICKY);
+  if (!n)
     {
       log(L_ERR "%s: Invalid remote address %I%J", p->p.name, cf->remote_ip, cf->iface);
       /* As we do not start yet, we can just disable protocol */
@@ -963,10 +981,14 @@ bgp_start_locked(struct object_lock *lock)
       return;
     }
 
-  if (p->neigh->scope > 0)
-    bgp_start_neighbor(p);
-  else
+  p->neigh = n;
+
+  if (n->scope <= 0)
     BGP_TRACE(D_EVENTS, "Waiting for %I%J to become my neighbor", cf->remote_ip, cf->iface);
+  else if (p->cf->check_link && !(n->iface->flags & IF_LINK_UP))
+    BGP_TRACE(D_EVENTS, "Waiting for link on %s", n->iface->name);
+  else
+    bgp_start_neighbor(p);
 }
 
 static int
@@ -1173,6 +1195,9 @@ bgp_check_config(struct bgp_config *c)
 		      ipa_is_link_local(c->source_addr)))
     cf_error("Multihop BGP cannot be used with link-local addresses");
 
+  if (c->multihop && c->check_link)
+    cf_error("Multihop BGP cannot depend on link state");
+
   if (c->multihop && c->bfd && ipa_zero(c->source_addr))
     cf_error("Multihop BGP with BFD requires specified source address");
 
@@ -1288,7 +1313,7 @@ bgp_store_error(struct bgp_proto *p, struct bgp_conn *c, u8 class, u32 code)
 
 static char *bgp_state_names[] = { "Idle", "Connect", "Active", "OpenSent", "OpenConfirm", "Established", "Close" };
 static char *bgp_err_classes[] = { "", "Error: ", "Socket: ", "Received: ", "BGP Error: ", "Automatic shutdown: ", ""};
-static char *bgp_misc_errors[] = { "", "Neighbor lost", "Invalid next hop", "Kernel MD5 auth failed", "No listening socket", "BFD session down", "Graceful restart"};
+static char *bgp_misc_errors[] = { "", "Neighbor lost", "Invalid next hop", "Kernel MD5 auth failed", "No listening socket", "Link down", "BFD session down", "Graceful restart"};
 static char *bgp_auto_errors[] = { "", "Route limit exceeded"};
 
 static const char *

proto/bgp/bgp.h

@@ -62,6 +62,7 @@ struct bgp_config {
 
   char *password;			/* Password used for MD5 authentication */
   struct rtable_config *igp_table;	/* Table used for recursive next hop lookups */
+  int check_link;			/* Use iface link state for liveness detection */
   int bfd;				/* Use BFD for liveness detection */
 };
 
@@ -335,8 +336,9 @@ void bgp_log_error(struct bgp_proto *p, u8 class, char *msg, unsigned code, unsi
 #define BEM_INVALID_NEXT_HOP	2
 #define BEM_INVALID_MD5		3	/* MD5 authentication kernel request failed (possibly not supported) */
 #define BEM_NO_SOCKET		4
-#define BEM_BFD_DOWN		5
-#define BEM_GRACEFUL_RESTART	6
+#define BEM_LINK_DOWN		5
+#define BEM_BFD_DOWN		6
+#define BEM_GRACEFUL_RESTART	7
 
 /* Automatic shutdown error codes */
 

proto/bgp/config.Y

@@ -26,7 +26,8 @@ CF_KEYWORDS(BGP, LOCAL, NEIGHBOR, AS, HOLD, TIME, CONNECT, RETRY,
 	PREFER, OLDER, MISSING, LLADDR, DROP, IGNORE, ROUTE, REFRESH,
 	INTERPRET, COMMUNITIES, BGP_ORIGINATOR_ID, BGP_CLUSTER_LIST, IGP,
 	TABLE, GATEWAY, DIRECT, RECURSIVE, MED, TTL, SECURITY, DETERMINISTIC,
-	SECONDARY, ALLOW, BFD, ADD, PATHS, RX, TX, GRACEFUL, RESTART, AWARE)
+	SECONDARY, ALLOW, BFD, ADD, PATHS, RX, TX, GRACEFUL, RESTART, AWARE,
+	CHECK, LINK)
 
 CF_GRAMMAR
 
@@ -123,6 +124,7 @@ bgp_proto:
  | bgp_proto GRACEFUL RESTART TIME expr ';' { BGP_CFG->gr_time = $5; }
  | bgp_proto IGP TABLE rtable ';' { BGP_CFG->igp_table = $4; }
  | bgp_proto TTL SECURITY bool ';' { BGP_CFG->ttl_security = $4; }
+ | bgp_proto CHECK LINK bool ';' { BGP_CFG->check_link = $4; }
  | bgp_proto BFD bool ';' { BGP_CFG->bfd = $3; cf_check_bfd($3); }
  ;