Enables multihop mode for IBGP by default.

This is more consistent with common usage and also with the behavior of
other implementations (Cisco, Juniper).

Also changes the default for gw mode to be based solely on
direct/multihop.

3 files changed, 51 insertions, 42 deletions

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 421be713..52520a7e 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -1536,33 +1536,37 @@ This allows to set routing policy and all the other parameters differently
 for each neighbor using the following configuration parameters:
 
 <descrip>
-	<tag>local [<m/ip/] as <m/number/</tag> Define which AS we
-	are part of. (Note that contrary to other IP routers, BIRD is
-	able to act as a router located in multiple AS'es
-	simultaneously, but in such cases you need to tweak the BGP
-	paths manually in the filters to get consistent behavior.)
-	Optional <cf/ip/ argument specifies a source address,
-	equivalent to the <cf/source address/ option (see below).
+	<tag>local [<m/ip/] as <m/number/</tag> Define which AS we are part
+	of. (Note that contrary to other IP routers, BIRD is able to act as a
+	router located in multiple AS'es simultaneously, but in such cases you
+	need to tweak the BGP paths manually in the filters to get consistent
+	behavior.) Optional <cf/ip/ argument specifies a source address,
+	equivalent to the <cf/source address/ option (see below).  This
+	parameter is mandatory.
+
+	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router this
+	instance will be talking to and what AS it's located in. In case the
+	neighbor is in the same AS as we are, we automatically switch to iBGP.
 	This parameter is mandatory.
 
-	<tag>neighbor <m/ip/ as <m/number/</tag> Define neighboring router
-	this instance will be talking to and what AS it's located in. Unless
-	you use the <cf/multihop/ clause, it must be directly connected to one
-	of your router's interfaces. In case the neighbor is in the same AS
-	as we are, we automatically switch to iBGP. This parameter is mandatory.
-
-	<tag>multihop [<m/number/]</tag> Configure multihop BGP
-	session to a neighbor that isn't directly connected.
-	Accurately, this option should be used if the configured
-	neighbor IP address does not match with any local network
-	subnets. Such IP address have to be reachable through system
-	routing table. For multihop BGP it is recommended to
-	explicitly configure <cf/source address/ to have it
-	stable. Optional <cf/number/ argument can be used to specify
-	the number of hops (used for TTL). Note that the number of
-	networks (edges) in a path is counted, i.e. if two BGP
-	speakers are separated by one router, the number of hops is
-	2. Default: switched off.
+	<tag>direct</tag> Specify that the neighbor is directly connected. The
+	IP address of the neighbor must be from a directly reachable IP range
+	(i.e. associated with one of your router's interfaces), otherwise the
+	BGP session wouldn't start but it would wait for such interface to
+	appear. The alternative is the <cf/multihop/ option.  Default: enabled
+	for eBGP.
+
+	<tag>multihop [<m/number/]</tag> Configure multihop BGP session to a
+	neighbor that isn't directly connected.  Accurately, this option should
+	be used if the configured neighbor IP address does not match with any
+	local network subnets. Such IP address have to be reachable through
+	system routing table.  The alternative is the <cf/direct/ option. For
+	multihop BGP it is recommended to explicitly configure the source
+	address to have it stable. Optional <cf/number/ argument can be used to
+	specify the number of hops (used for TTL). Note that the number of
+	networks (edges) in a path is counted; i.e., if two BGP speakers are
+	separated by one router, the number of hops is 2. Default: enabled for
+	iBGP.
 
 	<tag>source address <m/ip/</tag> Define local address we
 	should use for next hop calculation and as a source address
@@ -1609,8 +1613,8 @@ for each neighbor using the following configuration parameters:
 	table, and was used in older versions of BIRD, but does not
 	handle well nontrivial iBGP setups and multihop.  Recursive
 	mode is incompatible with <ref id="dsc-sorted" name="sorted
-	tables">. Default: <cf/direct/ for singlehop eBGP,
-	<cf/recursive/ otherwise.
+	tables">. Default: <cf/direct/ for direct sessions,
+	<cf/recursive/ for multihop sessions.
 
 	<tag>igp table <m/name/</tag> Specifies a table that is used
 	as an IGP routing table. Default: the same as the table BGP is
diff --git a/proto/bgp/bgp.c b/proto/bgp/bgp.c
index cc5318e8..f5b6b8fc 100644
--- a/proto/bgp/bgp.c
+++ b/proto/bgp/bgp.c
@@ -1006,6 +1006,24 @@ bgp_check_config(struct bgp_config *c)
   if (c->c.class == SYM_TEMPLATE)
     return;
 
+
+  /* EBGP direct by default, IBGP multihop by default */
+  if (c->multihop < 0)
+    c->multihop = internal ? 64 : 0;
+
+  /* Different default for gw_mode */
+  if (!c->gw_mode)
+    c->gw_mode = c->multihop ? GW_RECURSIVE : GW_DIRECT;
+
+  /* Different default based on rs_client */
+  if (!c->missing_lladdr)
+    c->missing_lladdr = c->rs_client ? MLL_IGNORE : MLL_SELF;
+
+  /* Disable after error incompatible with restart limit action */
+  if (c->c.in_limit && (c->c.in_limit->action == PLA_RESTART) && c->disable_after_error)
+    c->c.in_limit->action = PLA_DISABLE;
+
+
   if (!c->local_as)
     cf_error("Local AS number must be set");
 
@@ -1021,7 +1039,6 @@ bgp_check_config(struct bgp_config *c)
   if (internal && c->rs_client)
     cf_error("Only external neighbor can be RS client");
 
-
   if (c->multihop && (c->gw_mode == GW_DIRECT))
     cf_error("Multihop BGP cannot use direct gateway mode");
 
@@ -1032,20 +1049,6 @@ bgp_check_config(struct bgp_config *c)
   if (c->multihop && c->bfd && ipa_zero(c->source_addr))
     cf_error("Multihop BGP with BFD requires specified source address");
 
-
-  /* Different default based on rs_client */
-  if (!c->missing_lladdr)
-    c->missing_lladdr = c->rs_client ? MLL_IGNORE : MLL_SELF;
-
-  /* Different default for gw_mode */
-  if (!c->gw_mode)
-    c->gw_mode = (c->multihop || internal) ? GW_RECURSIVE : GW_DIRECT;
-
-  /* Disable after error incompatible with restart limit action */
-  if (c->c.in_limit && (c->c.in_limit->action == PLA_RESTART) && c->disable_after_error)
-    c->c.in_limit->action = PLA_DISABLE;
-
-
   if ((c->gw_mode == GW_RECURSIVE) && c->c.table->sorted)
     cf_error("BGP in recursive mode prohibits sorted table");
 
diff --git a/proto/bgp/config.Y b/proto/bgp/config.Y
index 185b1bda..e93501d3 100644
--- a/proto/bgp/config.Y
+++ b/proto/bgp/config.Y
@@ -34,6 +34,7 @@ CF_ADDTO(proto, bgp_proto '}' { bgp_check_config(BGP_CFG); } )
 
 bgp_proto_start: proto_start BGP {
      this_proto = proto_config_new(&proto_bgp, sizeof(struct bgp_config), $1);
+     BGP_CFG->multihop = -1;	/* undefined */
      BGP_CFG->hold_time = 240;
      BGP_CFG->connect_retry_time = 120;
      BGP_CFG->initial_hold_time = 240;
@@ -74,6 +75,7 @@ bgp_proto:
  | bgp_proto STARTUP HOLD TIME expr ';' { BGP_CFG->initial_hold_time = $5; }
  | bgp_proto CONNECT RETRY TIME expr ';' { BGP_CFG->connect_retry_time = $5; }
  | bgp_proto KEEPALIVE TIME expr ';' { BGP_CFG->keepalive_time = $4; }
+ | bgp_proto DIRECT ';' { BGP_CFG->multihop = 0; }
  | bgp_proto MULTIHOP ';' { BGP_CFG->multihop = 64; }
  | bgp_proto MULTIHOP expr ';' { BGP_CFG->multihop = $3; if (($3<1) || ($3>255)) cf_error("Multihop must be in range 1-255"); }
  | bgp_proto NEXT HOP SELF ';' { BGP_CFG->next_hop_self = 1; BGP_CFG->next_hop_keep = 0; }