Commit f3e59178 authored by Ondrej Zajicek's avatar Ondrej Zajicek
Browse files

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.
parent 52e030e1

doc/bird.sgml

+31 −27
Original line number Diff line number Diff line
@@ -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

proto/bgp/bgp.c

+18 −15
Original line number Diff line number Diff line
@@ -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");

proto/bgp/config.Y

+2 −0
Original line number Diff line number Diff line
@@ -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; }

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