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Enables multihop mode for IBGP by default.

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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.
This commit is contained in:
Ondrej Zajicek
2013-11-24 12:37:24 +01:00
parent 52e030e146
commit f3e5917850
3 changed files with 50 additions and 41 deletions
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doc/bird.sgml
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@@ -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>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. 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>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