bgpd: refine the setting up of GTSM

* bgpd.h: Add error code for setting GTSM on iBGP
* bgpd.c: (peer_ttl_security_hops_set) use previous error code and signal
  incompatibility of GTSM+iBGP to vty.
  Consider the session state when setting GTSM, and reset Open/Active peers
  to let them pick up new TTL from start.

3 files changed, 33 insertions, 8 deletions

diff --git a/bgpd/bgp_vty.c b/bgpd/bgp_vty.c
index d93c5d36..e7e7dba1 100644
--- a/bgpd/bgp_vty.c
+++ b/bgpd/bgp_vty.c
@@ -216,6 +216,9 @@ bgp_vty_return (struct vty *vty, int ret)
     case BGP_ERR_NO_EBGP_MULTIHOP_WITH_TTLHACK:
       str = "ebgp-multihop and ttl-security cannot be configured together";
       break;
+    case BGP_ERR_NO_IBGP_WITH_TTLHACK:
+      str = "ttl-security only allowed for EBGP peers";
+      break;
     }
   if (str)
     {
@@ -7643,10 +7646,16 @@ bgp_show_peer (struct vty *vty, struct peer *p)
 		 p->host, VTY_NEWLINE);
     }
 
-  /* EBGP Multihop */
-  if (peer_sort (p) != BGP_PEER_IBGP && p->ttl > 1)
-    vty_out (vty, "  External BGP neighbor may be up to %d hops away.%s",
-	     p->ttl, VTY_NEWLINE);
+  /* EBGP Multihop and GTSM */
+  if (peer_sort (p) != BGP_PEER_IBGP)
+    {
+      if (p->gtsm_hops > 0)
+	vty_out (vty, "  External BGP neighbor may be up to %d hops away.%s",
+		 p->gtsm_hops, VTY_NEWLINE);
+      else if (p->ttl > 1)
+	vty_out (vty, "  External BGP neighbor may be up to %d hops away.%s",
+		 p->ttl, VTY_NEWLINE);
+    }
 
   /* Local address. */
   if (p->su_local)
diff --git a/bgpd/bgpd.c b/bgpd/bgpd.c
index 5a412f23..ee0cc5da 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -4376,7 +4376,7 @@ peer_ttl_security_hops_set (struct peer *peer, int gtsm_hops)
   zlog_debug ("peer_ttl_security_hops_set: set gtsm_hops to %d for %s", gtsm_hops, peer->host);
 
   if (peer_sort (peer) == BGP_PEER_IBGP)
-    return 0;
+    return BGP_ERR_NO_IBGP_WITH_TTLHACK;
 
   /* We cannot configure ttl-security hops when ebgp-multihop is already
      set.  For non peer-groups, the check is simple.  For peer-groups, it's
@@ -4430,8 +4430,23 @@ peer_ttl_security_hops_set (struct peer *peer, int gtsm_hops)
 
 	  peer->gtsm_hops = group->conf->gtsm_hops;
 
-	  if (peer->fd >= 0 && peer->gtsm_hops != 0)
-            sockopt_minttl (peer->su.sa.sa_family, peer->fd, MAXTTL + 1 - peer->gtsm_hops);
+	  /* Change setting of existing peer
+	   *   established then change value (may break connectivity)
+	   *   not established yet (teardown session and restart)
+	   *   no session then do nothing (will get handled by next connection)
+	   */
+	  if (peer->status == Established)
+	    {
+	      if (peer->fd >= 0 && peer->gtsm_hops != 0)
+		sockopt_minttl (peer->su.sa.sa_family, peer->fd,
+				MAXTTL + 1 - peer->gtsm_hops);
+	    }
+	  else if (peer->status < Established)
+	    {
+	      if (BGP_DEBUG (events, EVENTS))
+		zlog_debug ("%s Min-ttl changed", peer->host);
+	      BGP_EVENT_ADD (peer, BGP_Stop);
+	    }
 	}
     }
 
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index 39cdf8eb..4da19e71 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -802,7 +802,8 @@ enum bgp_clear_type
 #define BGP_ERR_CANNOT_HAVE_LOCAL_AS_SAME_AS    -28
 #define BGP_ERR_TCPSIG_FAILED			-29
 #define BGP_ERR_NO_EBGP_MULTIHOP_WITH_TTLHACK	-30
-#define BGP_ERR_MAX				-31
+#define BGP_ERR_NO_IBGP_WITH_TTLHACK		-31
+#define BGP_ERR_MAX				-32
 
 extern struct bgp_master *bm;