doc: add clicmd role for frr cli

[mirror_frr.git] / doc / user / bgp.rst

.. _BGP:

***
BGP
***

:abbr:`BGP` stands for a Border Gateway Protocol. The lastest BGP version is 4.
It is referred as BGP-4. BGP-4 is one of the Exterior Gateway Protocols and
de-fact standard of Inter Domain routing protocol.  BGP-4 is described in
:rfc:`1771`.

Many extensions have been added to :rfc:`1771`. :rfc:`2858` provides
multiprotocol support to BGP-4.

.. _Starting_BGP:

Starting BGP
============

Default configuration file of *bgpd* is :file:`bgpd.conf`.
*bgpd* searches the current directory first then
|INSTALL_PREFIX_ETC|/bgpd.conf. All of bgpd's command must be
configured in :file:`bgpd.conf`.

*bgpd* specific invocation options are described below. Common
options may also be specified (:ref:`Common_Invocation_Options`).



*-p `PORT`*

*--bgp_port=`PORT`*
  Set the bgp protocol's port number.


*-r*

*--retain*
  When program terminates, retain BGP routes added by zebra.


*-l*

*--listenon*
  Specify a specific IP address for bgpd to listen on, rather than its
  default of INADDR_ANY / IN6ADDR_ANY. This can be useful to constrain bgpd
  to an internal address, or to run multiple bgpd processes on one host.


.. _BGP_router:

BGP router
==========

First of all you must configure BGP router with *router bgp*
command. To configure BGP router, you need AS number. AS number is an
identification of autonomous system. BGP protocol uses the AS number
for detecting whether the BGP connection is internal one or external one.

.. index:: router bgp ASN

``router bgp ASN``
  Enable a BGP protocol process with the specified `asn`. After
  this statement you can input any `BGP Commands`. You can not
  create different BGP process under different `asn` without
  specifying `multiple-instance` (:ref:`Multiple_instance`).

.. index:: no router bgp ASN

``no router bgp ASN``
  Destroy a BGP protocol process with the specified `asn`.

.. index:: bgp router-id `A.B.C.D`

``bgp router-id `A.B.C.D```

  This command specifies the router-ID. If *bgpd* connects to *zebra* it gets
  interface and address information. In that case default router ID value
  is selected as the largest IP Address of the interfaces. When
  `router zebra` is not enabled *bgpd* can't get interface information
  so `router-id` is set to 0.0.0.0. So please set router-id by hand.

.. _BGP_distance:

BGP distance
------------

.. index:: distance bgp <1-255> <1-255> <1-255>

``distance bgp <1-255> <1-255> <1-255>``

  This command change distance value of BGP. Each argument is distance
  value for external routes, internal routes and local routes.

.. index:: distance <1-255> `A.B.C.D/M`

``distance <1-255> `A.B.C.D/M```

.. index:: distance <1-255> `A.B.C.D/M` `word`

``distance <1-255> `A.B.C.D/M` `word```

    This command set distance value to

.. _BGP_decision_process:

BGP decision process
--------------------

The decision process FRR BGP uses to select routes is as follows:



*1. Weight check*
  prefer higher local weight routes to lower routes.


*2. Local preference check*
  prefer higher local preference routes to lower.


*3. Local route check*
  Prefer local routes (statics, aggregates, redistributed) to received routes.


*4. AS path length check*
  Prefer shortest hop-count AS_PATHs.


*5. Origin check*
  Prefer the lowest origin type route. That is, prefer IGP origin routes to
  EGP, to Incomplete routes.


*6. MED check*
  Where routes with a MED were received from the same AS,
  prefer the route with the lowest MED. :ref:`BGP_MED`.


*7. External check*
  Prefer the route received from an external, eBGP peer
  over routes received from other types of peers.


*8. IGP cost check*
  Prefer the route with the lower IGP cost.


*9. Multi-path check*
  If multi-pathing is enabled, then check whether
  the routes not yet distinguished in preference may be considered equal. If
  :ref:`bgp_bestpath_as-path_multipath-relax` is set, all such routes are
  considered equal, otherwise routes received via iBGP with identical AS_PATHs
  or routes received from eBGP neighbours in the same AS are considered equal.


*10 Already-selected external check*
  Where both routes were received from eBGP peers, then prefer the route which
  is already selected. Note that this check is not applied if :ref:`bgp_bestpath_compare-routerid` is configured. This check can prevent some cases
  of oscillation.


*11. Router-ID check*
  Prefer the route with the lowest `router-ID`. If the
  route has an `ORIGINATOR_ID` attribute, through iBGP reflection, then that
  router ID is used, otherwise the `router-ID` of the peer the route was
  received from is used.


*12. Cluster-List length check*
  The route with the shortest cluster-list
  length is used. The cluster-list reflects the iBGP reflection path the
  route has taken.


*13. Peer address*
  Prefer the route received from the peer with the higher
  transport layer address, as a last-resort tie-breaker.


.. index:: bgp bestpath as-path confed

``bgp bestpath as-path confed``

  This command specifies that the length of confederation path sets and
  sequences should should be taken into account during the BGP best path
  decision process.

.. index:: bgp bestpath as-path multipath-relax

``bgp bestpath as-path multipath-relax``

  .. _bgp_bestpath_as-path_multipath-relax:

  This command specifies that BGP decision process should consider paths
  of equal AS_PATH length candidates for multipath computation. Without
  the knob, the entire AS_PATH must match for multipath computation.

.. index:: bgp bestpath compare-routerid

``bgp bestpath compare-routerid``

  .. _bgp_bestpath_compare-routerid:

  Ensure that when comparing routes where both are equal on most metrics,
  including local-pref, AS_PATH length, IGP cost, MED, that the tie is broken
  based on router-ID.

  If this option is enabled, then the already-selected check, where
  already selected eBGP routes are preferred, is skipped.

  If a route has an `ORIGINATOR_ID` attribute because it has been reflected,
  that `ORIGINATOR_ID` will be used. Otherwise, the router-ID of the peer the
  route was received from will be used.

  The advantage of this is that the route-selection (at this point) will be
  more deterministic. The disadvantage is that a few or even one lowest-ID
  router may attract all trafic to otherwise-equal paths because of this
  check. It may increase the possibility of MED or IGP oscillation, unless
  other measures were taken to avoid these. The exact behaviour will be
  sensitive to the iBGP and reflection topology.


.. _BGP_route_flap_dampening:

BGP route flap dampening
------------------------

.. index:: bgp dampening `<1-45>` `<1-20000>` `<1-20000>` `<1-255>`

``bgp dampening `<1-45>` `<1-20000>` `<1-20000>` `<1-255>```

  This command enables BGP route-flap dampening and specifies dampening parameters.


*@asis{half-life}*
    Half-life time for the penalty

*@asis{reuse-threshold}*
    Value to start reusing a route

*@asis{suppress-threshold}*
    Value to start suppressing a route

*@asis{max-suppress}*
    Maximum duration to suppress a stable route

  The route-flap damping algorithm is compatible with :rfc:`2439`. The use of this command
  is not recommended nowadays, see http://www.ripe.net/ripe/docs/ripe-378,,RIPE-378 <http://www.ripe.net/ripe/docs/ripe-378,,RIPE-378>.

.. _BGP_MED:

BGP MED
=======

The BGP :abbr:`MED (Multi Exit Discriminator)` attribute has properties which can
cause subtle convergence problems in BGP. These properties and problems
have proven to be hard to understand, at least historically, and may still
not be widely understood. The following attempts to collect together and
present what is known about MED, to help operators and FRR users in
designing and configuring their networks.

The BGP :abbr:`MED` attribute is intended to allow one AS to indicate its
preferences for its ingress points to another AS. The MED attribute will not be
propagated on to another AS by the receiving AS - it is 'non-transitive' in the
BGP sense.

E.g., if AS X and AS Y have 2 different BGP peering points, then AS X
might set a MED of 100 on routes advertised at one and a MED of 200 at the
other. When AS Y selects between otherwise equal routes to or via
AS X, AS Y should prefer to take the path via the lower MED peering of 100 with
AS X. Setting the MED allows an AS to influence the routing taken to it
within another, neighbouring AS.

In this use of MED it is not really meaningful to compare the MED value on
routes where the next AS on the paths differs. E.g., if AS Y also had a
route for some destination via AS Z in addition to the routes from AS X, and
AS Z had also set a MED, it wouldn't make sense for AS Y to compare AS Z's
MED values to those of AS X. The MED values have been set by different
administrators, with different frames of reference.

The default behaviour of BGP therefore is to not compare MED values across
routes received from different neighbouring ASes. In FRR this is done by
comparing the neighbouring, left-most AS in the received AS_PATHs of the
routes and only comparing MED if those are the same.

@ifnottex
@macro mprec{}
@math{<}
@end macro
@end ifnottex

Unfortunately, this behaviour of MED, of sometimes being compared across
routes and sometimes not, depending on the properties of those other routes,
means MED can cause the order of preference over all the routes to be
undefined. That is, given routes A, B, and C, if A is preferred to B, and B
is preferred to C, then a well-defined order should mean the preference is
transitive (in the sense of orders @footnote{For some set of objects to have
an order, there *must* be some binary ordering relation that is defined
for *every* combination of those objects, and that relation *must*
be transitive. I.e.@:, if the relation operator is @mprec{}, and if
a @mprec{} b and b @mprec{} c then that relation must carry over
and it *must* be that a @mprec{} c for the objects to have an
order. The ordering relation may allow for equality, i.e.
a @mprec{} b and b @mprec{} a may both be true amd imply that
a and b are equal in the order and not distinguished by it, in
which case the set has a partial order. Otherwise, if there is an order,
all the objects have a distinct place in the order and the set has a total
order.}) and that A would be preferred to C.

However, when MED is involved this need not be the case. With MED it is
possible that C is actually preferred over A. So A is preferred to B, B is
preferred to C, but C is preferred to A. This can be true even where BGP
defines a deterministic 'most preferred' route out of the full set of
A,B,C. With MED, for any given set of routes there may be a
deterministically preferred route, but there need not be any way to arrange
them into any order of preference. With unmodified MED, the order of
preference of routes literally becomes undefined.

That MED can induce non-transitive preferences over routes can cause issues.
Firstly, it may be perceived to cause routing table churn locally at
speakers; secondly, and more seriously, it may cause routing instability in
iBGP topologies, where sets of speakers continually oscillate between
different paths.

The first issue arises from how speakers often implement routing decisions.
Though BGP defines a selection process that will deterministically select
the same route as best at any given speaker, even with MED, that process
requires evaluating all routes together. For performance and ease of
implementation reasons, many implementations evaluate route preferences in a
pair-wise fashion instead. Given there is no well-defined order when MED is
involved, the best route that will be chosen becomes subject to
implementation details, such as the order the routes are stored in. That
may be (locally) non-deterministic, e.g.@: it may be the order the routes
were received in.

This indeterminism may be considered undesirable, though it need not cause
problems. It may mean additional routing churn is perceived, as sometimes
more updates may be produced than at other times in reaction to some event .

This first issue can be fixed with a more deterministic route selection that
ensures routes are ordered by the neighbouring AS during selection.
:ref:`bgp_deterministic-med`. This may reduce the number of updates as
routes are received, and may in some cases reduce routing churn. Though, it
could equally deterministically produce the largest possible set of updates
in response to the most common sequence of received updates.

A deterministic order of evaluation tends to imply an additional overhead of
sorting over any set of n routes to a destination. The implementation of
deterministic MED in FRR scales significantly worse than most sorting
algorithms at present, with the number of paths to a given destination.
That number is often low enough to not cause any issues, but where there are
many paths, the deterministic comparison may quickly become increasingly
expensive in terms of CPU.

Deterministic local evaluation can *not* fix the second, more major,
issue of MED however. Which is that the non-transitive preference of routes
MED can cause may lead to routing instability or oscillation across multiple
speakers in iBGP topologies. This can occur with full-mesh iBGP, but is
particularly problematic in non-full-mesh iBGP topologies that further
reduce the routing information known to each speaker. This has primarily
been documented with iBGP route-reflection topologies. However, any
route-hiding technologies potentially could also exacerbate oscillation with
MED.

This second issue occurs where speakers each have only a subset of routes,
and there are cycles in the preferences between different combinations of
routes - as the undefined order of preference of MED allows - and the routes
are distributed in a way that causes the BGP speakers to 'chase' those
cycles. This can occur even if all speakers use a deterministic order of
evaluation in route selection.

E.g., speaker 4 in AS A might receive a route from speaker 2 in AS X, and
from speaker 3 in AS Y; while speaker 5 in AS A might receive that route
from speaker 1 in AS Y. AS Y might set a MED of 200 at speaker 1, and 100
at speaker 3. I.e, using ASN:ID:MED to label the speakers:

::

       /---------------\\
   X:2------|--A:4-------A:5--|-Y:1:200
   Y:3:100--|-/   |
       \\---------------/



Assuming all other metrics are equal (AS_PATH, ORIGIN, 0 IGP costs), then
based on the RFC4271 decision process speaker 4 will choose X:2 over
Y:3:100, based on the lower ID of 2. Speaker 4 advertises X:2 to speaker 5.
Speaker 5 will continue to prefer Y:1:200 based on the ID, and advertise
this to speaker 4. Speaker 4 will now have the full set of routes, and the
Y:1:200 it receives from 5 will beat X:2, but when speaker 4 compares
Y:1:200 to Y:3:100 the MED check now becomes active as the ASes match, and
now Y:3:100 is preferred. Speaker 4 therefore now advertises Y:3:100 to 5,
which will also agrees that Y:3:100 is preferred to Y:1:200, and so
withdraws the latter route from 4. Speaker 4 now has only X:2 and Y:3:100,
and X:2 beats Y:3:100, and so speaker 4 implicitly updates its route to
speaker 5 to X:2. Speaker 5 sees that Y:1:200 beats X:2 based on the ID,
and advertises Y:1:200 to speaker 4, and the cycle continues.

The root cause is the lack of a clear order of preference caused by how MED
sometimes is and sometimes is not compared, leading to this cycle in the
preferences between the routes:

::

   /---> X:2 ---beats---> Y:3:100 --\\
  |    |
  |    |
   \\---beats--- Y:1:200 <---beats---/



This particular type of oscillation in full-mesh iBGP topologies can  be
avoided by speakers preferring already selected, external routes rather than
choosing to update to new a route based on a post-MED metric (e.g.
router-ID), at the cost of a non-deterministic selection process. FRR
implements this, as do many other implementations, so long as it is not
overridden by setting :ref:`bgp_bestpath_compare-routerid`, and see also
:ref:`BGP_decision_process`, .

However, more complex and insidious cycles of oscillation are possible with
iBGP route-reflection, which are not so easily avoided. These have been
documented in various places. See, e.g., @cite{McPherson, D. and Gill, V.
and Walton, D., "Border Gateway Protocol (BGP) Persistent Route Oscillation
Condition", IETF RFC3345}, and @cite{Flavel, A. and M. Roughan, "Stable
and flexible iBGP", ACM SIGCOMM 2009}, and @cite{Griffin, T. and G. Wilfong,
"On the correctness of IBGP configuration", ACM SIGCOMM 2002} for concrete
examples and further references.

There is as of this writing *no* known way to use MED for its original
purpose; *and* reduce routing information in iBGP topologies;
*and* be sure to avoid the instability problems of MED due the
non-transitive routing preferences it can induce; in general on arbitrary
networks.

There may be iBGP topology specific ways to reduce the instability risks,
even while using MED, e.g.@: by constraining the reflection topology and by
tuning IGP costs between route-reflector clusters, see RFC3345 for details.
In the near future, the Add-Path extension to BGP may also solve MED
oscillation while still allowing MED to be used as intended, by distributing
"best-paths per neighbour AS". This would be at the cost of distributing at
least as many routes to all speakers as a full-mesh iBGP would, if not more,
while also imposing similar CPU overheads as the "Deterministic MED" feature
at each Add-Path reflector.

More generally, the instability problems that MED can introduce on more
complex, non-full-mesh, iBGP topologies may be avoided either by:


*
  Setting :ref:`bgp_always-compare-med`, however this allows MED to be compared
  across values set by different neighbour ASes, which may not produce
  coherent desirable results, of itself.

*
  Effectively ignoring MED by setting MED to the same value (e.g.@: 0) using
  :ref:`routemap_set_metric` on all received routes, in combination with
  setting :ref:`bgp_always-compare-med` on all speakers. This is the simplest
  and most performant way to avoid MED oscillation issues, where an AS is happy
  not to allow neighbours to inject this problematic metric.


As MED is evaluated after the AS_PATH length check, another possible use for
MED is for intra-AS steering of routes with equal AS_PATH length, as an
extension of the last case above. As MED is evaluated before IGP metric,
this can allow cold-potato routing to be implemented to send traffic to
preferred hand-offs with neighbours, rather than the closest hand-off
according to the IGP metric.

Note that even if action is taken to address the MED non-transitivity
issues, other oscillations may still be possible. E.g., on IGP cost if
iBGP and IGP topologies are at cross-purposes with each other - see the
Flavel and Roughan paper above for an example. Hence the guideline that the
iBGP topology should follow the IGP topology.

.. index:: bgp deterministic-med

``bgp deterministic-med``

  .. _bgp_deterministic-med:

  Carry out route-selection in way that produces deterministic answers
  locally, even in the face of MED and the lack of a well-defined order of
  preference it can induce on routes. Without this option the preferred route
  with MED may be determined largely by the order that routes were received
  in.

  Setting this option will have a performance cost that may be noticeable when
  there are many routes for each destination. Currently in FRR it is
  implemented in a way that scales poorly as the number of routes per
  destination increases.

  The default is that this option is not set.

Note that there are other sources of indeterminism in the route selection
process, specifically, the preference for older and already selected routes
from eBGP peers, :ref:`BGP_decision_process`.

.. index:: bgp always-compare-med

``bgp always-compare-med``

  .. _bgp_always-compare-med:

  Always compare the MED on routes, even when they were received from
  different neighbouring ASes. Setting this option makes the order of
  preference of routes more defined, and should eliminate MED induced
  oscillations.

  If using this option, it may also be desirable to use :ref:`routemap_set_metric` to set MED to 0 on routes received from external neighbours.

  This option can be used, together with :ref:`routemap_set_metric` to use MED
  as an intra-AS metric to steer equal-length AS_PATH routes to, e.g., desired
  exit points.

.. _BGP_network:

BGP network
===========


.. _BGP_route:

BGP route
---------

.. index:: network `A.B.C.D/M`

``network `A.B.C.D/M```

  This command adds the announcement network.::

    router bgp 1
     address-family ipv4 unicast
      network 10.0.0.0/8
     exit-address-family

  This configuration example says that network 10.0.0.0/8 will be
  announced to all neighbors. Some vendors' routers don't advertise
  routes if they aren't present in their IGP routing tables; `bgpd`
  doesn't care about IGP routes when announcing its routes.

.. index:: no network `A.B.C.D/M`

``no network `A.B.C.D/M```


.. _Route_Aggregation:

Route Aggregation
-----------------

.. index:: aggregate-address `A.B.C.D/M`

``aggregate-address `A.B.C.D/M```

  This command specifies an aggregate address.

.. index:: aggregate-address `A.B.C.D/M` as-set

``aggregate-address `A.B.C.D/M` as-set``

  This command specifies an aggregate address. Resulting routes include
  AS set.

.. index:: aggregate-address `A.B.C.D/M` summary-only

``aggregate-address `A.B.C.D/M` summary-only``

  This command specifies an aggregate address. Aggreated routes will
  not be announce.

.. index:: no aggregate-address `A.B.C.D/M`

``no aggregate-address `A.B.C.D/M```


.. _Redistribute_to_BGP:

Redistribute to BGP
-------------------

.. index:: redistribute kernel

``redistribute kernel``

  Redistribute kernel route to BGP process.

.. index:: redistribute static

``redistribute static``

  Redistribute static route to BGP process.

.. index:: redistribute connected

``redistribute connected``

  Redistribute connected route to BGP process.

.. index:: redistribute rip

``redistribute rip``

  Redistribute RIP route to BGP process.

.. index:: redistribute ospf

``redistribute ospf``

  Redistribute OSPF route to BGP process.

.. index:: redistribute vpn

``redistribute vpn``

  Redistribute VNC routes to BGP process.

.. index:: update-delay `max-delay`

``update-delay `max-delay```

.. index:: update-delay `max-delay` `establish-wait`

``update-delay `max-delay` `establish-wait```

    This feature is used to enable read-only mode on BGP process restart or when
    BGP process is cleared using 'clear ip bgp \*'. When applicable, read-only mode
    would begin as soon as the first peer reaches Established status and a timer
    for max-delay seconds is started.

    During this mode BGP doesn't run any best-path or generate any updates to its
    peers. This mode continues until:
    1. All the configured peers, except the shutdown peers, have sent explicit EOR
    (End-Of-RIB) or an implicit-EOR. The first keep-alive after BGP has reached
    Established is considered an implicit-EOR.
    If the establish-wait optional value is given, then BGP will wait for
    peers to reach established from the begining of the update-delay till the
    establish-wait period is over, i.e. the minimum set of established peers for
    which EOR is expected would be peers established during the establish-wait
    window, not necessarily all the configured neighbors.
    2. max-delay period is over.
    On hitting any of the above two conditions, BGP resumes the decision process
    and generates updates to its peers.

    Default max-delay is 0, i.e. the feature is off by default.

.. index:: table-map `route-map-name`

``table-map `route-map-name```

    This feature is used to apply a route-map on route updates from BGP to Zebra.
    All the applicable match operations are allowed, such as match on prefix,
    next-hop, communities, etc. Set operations for this attach-point are limited
    to metric and next-hop only. Any operation of this feature does not affect
    BGPs internal RIB.

    Supported for ipv4 and ipv6 address families. It works on multi-paths as well,
    however, metric setting is based on the best-path only.

.. _BGP_Peer:

BGP Peer
========


.. _Defining_Peer:

Defining Peer
-------------

.. index:: neighbor `peer` remote-as `asn`

``neighbor `peer` remote-as `asn```

  Creates a new neighbor whose remote-as is `asn`. `peer`
  can be an IPv4 address or an IPv6 address.::

    router bgp 1
     neighbor 10.0.0.1 remote-as 2

  In this case my router, in AS-1, is trying to peer with AS-2 at
  10.0.0.1.

  This command must be the first command used when configuring a neighbor.
  If the remote-as is not specified, *bgpd* will complain like this:::

    can't find neighbor 10.0.0.1


.. _BGP_Peer_commands:

BGP Peer commands
-----------------

In a `router bgp` clause there are neighbor specific configurations
required.

.. index:: neighbor `peer` shutdown

``neighbor `peer` shutdown``

.. index:: no neighbor `peer` shutdown

``no neighbor `peer` shutdown``

    Shutdown the peer. We can delete the neighbor's configuration by
    `no neighbor `peer` remote-as @var{as-number`} but all
    configuration of the neighbor will be deleted. When you want to
    preserve the configuration, but want to drop the BGP peer, use this
    syntax.

.. index:: neighbor `peer` ebgp-multihop

``neighbor `peer` ebgp-multihop``

.. index:: no neighbor `peer` ebgp-multihop

``no neighbor `peer` ebgp-multihop``

.. index:: neighbor `peer` description ...

``neighbor `peer` description ...``

.. index:: no neighbor `peer` description ...

``no neighbor `peer` description ...``

  Set description of the peer.

.. index:: neighbor `peer` version `version`

``neighbor `peer` version `version```

  Set up the neighbor's BGP version. `version` can be `4`,
  `4+` or `4-`. BGP version `4` is the default value used for
  BGP peering. BGP version `4+` means that the neighbor supports
  Multiprotocol Extensions for BGP-4. BGP version `4-` is similar but
  the neighbor speaks the old Internet-Draft revision 00's Multiprotocol
  Extensions for BGP-4. Some routing software is still using this
  version.

.. index:: neighbor `peer` interface `ifname`

``neighbor `peer` interface `ifname```

.. index:: no neighbor `peer` interface `ifname`

``no neighbor `peer` interface `ifname```

  When you connect to a BGP peer over an IPv6 link-local address, you
  have to specify the `ifname` of the interface used for the
  connection. To specify IPv4 session addresses, see the
  `neighbor `peer` update-source` command below.

  This command is deprecated and may be removed in a future release. Its
  use should be avoided.

.. index:: neighbor `peer` next-hop-self [all]

``neighbor `peer` next-hop-self [all]``

.. index:: no neighbor `peer` next-hop-self [all]

``no neighbor `peer` next-hop-self [all]``

      This command specifies an announced route's nexthop as being equivalent
      to the address of the bgp router if it is learned via eBGP.
      If the optional keyword `all` is specified the modifiation is done
      also for routes learned via iBGP.

.. index:: neighbor `peer` update-source `<ifname|address>`

``neighbor `peer` update-source `<ifname|address>```

.. index:: no neighbor `peer` update-source

``no neighbor `peer` update-source``

  Specify the IPv4 source address to use for the :abbr:`BGP` session to this
  neighbour, may be specified as either an IPv4 address directly or
  as an interface name (in which case the *zebra* daemon MUST be running
  in order for *bgpd* to be able to retrieve interface state).::

    router bgp 64555
     neighbor foo update-source 192.168.0.1
     neighbor bar update-source lo0


.. index:: neighbor `peer` default-originate

``neighbor `peer` default-originate``

.. index:: no neighbor `peer` default-originate

``no neighbor `peer` default-originate``

    *bgpd*'s default is to not announce the default route (0.0.0.0/0) even it
    is in routing table. When you want to announce default routes to the
    peer, use this command.

.. index:: neighbor `peer` port `port`

``neighbor `peer` port `port```

.. index:: neighbor `peer` port `port`

``neighbor `peer` port `port```

.. index:: neighbor `peer` send-community

``neighbor `peer` send-community``

.. index:: neighbor `peer` send-community

``neighbor `peer` send-community``

.. index:: neighbor `peer` weight `weight`

``neighbor `peer` weight `weight```

.. index:: no neighbor `peer` weight `weight`

``no neighbor `peer` weight `weight```

    This command specifies a default `weight` value for the neighbor's
    routes.

.. index:: neighbor `peer` maximum-prefix `number`

``neighbor `peer` maximum-prefix `number```

.. index:: no neighbor `peer` maximum-prefix `number`

``no neighbor `peer` maximum-prefix `number```

.. index:: neighbor `peer` local-as `as-number`

``neighbor `peer` local-as `as-number```

.. index:: neighbor `peer` local-as `as-number` no-prepend

``neighbor `peer` local-as `as-number` no-prepend``

.. index:: neighbor `peer` local-as `as-number` no-prepend replace-as

``neighbor `peer` local-as `as-number` no-prepend replace-as``

.. index:: no neighbor `peer` local-as

``no neighbor `peer` local-as``

      Specify an alternate AS for this BGP process when interacting with the
      specified peer. With no modifiers, the specified local-as is prepended to
      the received AS_PATH when receiving routing updates from the peer, and
      prepended to the outgoing AS_PATH (after the process local AS) when
      transmitting local routes to the peer.

      If the no-prepend attribute is specified, then the supplied local-as is not
      prepended to the received AS_PATH.

      If the replace-as attribute is specified, then only the supplied local-as is
      prepended to the AS_PATH when transmitting local-route updates to this peer.

      Note that replace-as can only be specified if no-prepend is.

      This command is only allowed for eBGP peers.

.. index:: neighbor `peer` ttl-security hops `number`

``neighbor `peer` ttl-security hops `number```

.. index:: no neighbor `peer` ttl-security hops `number`

``no neighbor `peer` ttl-security hops `number```

  This command enforces Generalized TTL Security Mechanism (GTSM), as
  specified in RFC 5082. With this command, only neighbors that are the
  specified number of hops away will be allowed to become neighbors. This
  command is mututally exclusive with *ebgp-multihop*.

.. _Peer_filtering:

Peer filtering
--------------

.. index:: neighbor `peer` distribute-list `name` [in|out]

``neighbor `peer` distribute-list `name` [in|out]``

  This command specifies a distribute-list for the peer. `direct` is
  ``in`` or ``out``.

.. index:: neighbor PEER prefix-list NAME [in|out]

``neighbor PEER prefix-list NAME [in|out]``
.. index:: neighbor PEER filter-list NAME [in|out]

``neighbor PEER filter-list NAME [in|out]``
.. index:: neighbor `peer` route-map `name` [in|out]

``neighbor `peer` route-map `name` [in|out]``

  Apply a route-map on the neighbor. `direct` must be `in` or
  `out`.

.. index:: bgp route-reflector allow-outbound-policy

``bgp route-reflector allow-outbound-policy``

  By default, attribute modification via route-map policy out is not reflected
  on reflected routes. This option allows the modifications to be reflected as
  well. Once enabled, it affects all reflected routes.

.. _BGP_Peer_Group:

BGP Peer Group
==============

.. index:: neighbor `word` peer-group

``neighbor `word` peer-group``

  This command defines a new peer group.

.. index:: neighbor `peer` peer-group `word`

``neighbor `peer` peer-group `word```

  This command bind specific peer to peer group `word`.

.. _BGP_Address_Family:

BGP Address Family
==================

Multiprotocol BGP enables BGP to carry routing information for multiple
Network Layer protocols. BGP supports multiple Address Family
Identifier (AFI), namely IPv4 and IPv6. Support is also provided for
multiple sets of per-AFI information via Subsequent Address Family
Identifiers (SAFI). In addition to unicast information, VPN information
:rfc:`4364` and :rfc:`4659`, and Encapsulation information
:rfc:`5512` is supported.

.. index:: show ip bgp vpnv4 all

``show ip bgp vpnv4 all``
.. index:: show ipv6 bgp vpn all

``show ipv6 bgp vpn all``
    Print active IPV4 or IPV6 routes advertised via the VPN SAFI.

.. index:: show ip bgp encap all

``show ip bgp encap all``
.. index:: show ipv6 bgp encap all

``show ipv6 bgp encap all``
      Print active IPV4 or IPV6 routes advertised via the Encapsulation SAFI.

.. index:: show bgp ipv4 encap summary

``show bgp ipv4 encap summary``
.. index:: show bgp ipv4 vpn summary

``show bgp ipv4 vpn summary``
.. index:: show bgp ipv6 encap summary

``show bgp ipv6 encap summary``
.. index:: show bgp ipv6 vpn summary

``show bgp ipv6 vpn summary``
      Print a summary of neighbor connections for the specified AFI/SAFI combination.

.. _Autonomous_System:

Autonomous System
=================

The :abbr:`AS (Autonomous System)` number is one of the essential
element of BGP. BGP is a distance vector routing protocol, and the
AS-Path framework provides distance vector metric and loop detection to
BGP. @cite{RFC1930, Guidelines for creation, selection, and
registration of an Autonomous System (AS)} provides some background on
the concepts of an AS.

The AS number is a two octet value, ranging in value from 1 to 65535.
The AS numbers 64512 through 65535 are defined as private AS numbers.
Private AS numbers must not to be advertised in the global Internet.

.. _Display_BGP_Routes_by_AS_Path:

Display BGP Routes by AS Path
-----------------------------

To show BGP routes which has specific AS path information `show ip bgp` command can be used.

.. index:: show bgp ipv4|ipv6 regexp LINE

``show bgp ipv4|ipv6 regexp LINE``
  This commands displays BGP routes that matches a regular
  expression `line` (:ref:`BGP_Regular_Expressions`).

.. _AS_Path_Access_List:

AS Path Access List
-------------------

AS path access list is user defined AS path.

.. index:: ip as-path access-list WORD permit|deny LINE

``ip as-path access-list WORD permit|deny LINE``
  This command defines a new AS path access list.

.. index:: no ip as-path access-list WORD

``no ip as-path access-list WORD``
.. index:: no ip as-path access-list WORD permit|deny LINE

``no ip as-path access-list WORD permit|deny LINE``

.. _Using_AS_Path_in_Route_Map:

Using AS Path in Route Map
--------------------------

.. index:: match as-path WORD

``match as-path WORD``

.. index:: set as-path prepend AS-PATH

``set as-path prepend AS-PATH``
  Prepend the given string of AS numbers to the AS_PATH.

.. index:: set as-path prepend last-as NUM

``set as-path prepend last-as NUM``
  Prepend the existing last AS number (the leftmost ASN) to the AS_PATH.

.. _Private_AS_Numbers:

Private AS Numbers
------------------


.. _BGP_Communities_Attribute:

BGP Communities Attribute
=========================

BGP communities attribute is widely used for implementing policy
routing. Network operators can manipulate BGP communities attribute
based on their network policy. BGP communities attribute is defined
in :t:`RFC1997, BGP Communities Attribute` and
@cite{RFC1998, An Application of the BGP Community Attribute
in Multi-home Routing}. It is an optional transitive attribute,
therefore local policy can travel through different autonomous system.

Communities attribute is a set of communities values. Each
communities value is 4 octet long. The following format is used to
define communities value.



*AS:VAL*
  This format represents 4 octet communities value. `AS` is high
  order 2 octet in digit format. `VAL` is low order 2 octet in
  digit format. This format is useful to define AS oriented policy
  value. For example, `7675:80` can be used when AS 7675 wants to
  pass local policy value 80 to neighboring peer.

*internet*
  `internet` represents well-known communities value 0.

*no-export*
  ``no-export`` represents well-known communities value ``NO_EXPORT`` @\*
  @r{(0xFFFFFF01)}. All routes carry this value must not be advertised
  to outside a BGP confederation boundary. If neighboring BGP peer is
  part of BGP confederation, the peer is considered as inside a BGP
  confederation boundary, so the route will be announced to the peer.

*no-advertise*
  ``no-advertise`` represents well-known communities value
  ``NO_ADVERTISE`` @*@r{(0xFFFFFF02)}. All routes carry this value
  must not be advertise to other BGP peers.

*local-AS*
  ``local-AS`` represents well-known communities value
  ``NO_EXPORT_SUBCONFED`` @r{(0xFFFFFF03)}. All routes carry this
  value must not be advertised to external BGP peers. Even if the
  neighboring router is part of confederation, it is considered as
  external BGP peer, so the route will not be announced to the peer.

When BGP communities attribute is received, duplicated communities
value in the communities attribute is ignored and each communities
values are sorted in numerical order.

.. _BGP_Community_Lists:

BGP Community Lists
-------------------

BGP community list is a user defined BGP communites attribute list.
BGP community list can be used for matching or manipulating BGP
communities attribute in updates.

There are two types of community list. One is standard community
list and another is expanded community list. Standard community list
defines communities attribute. Expanded community list defines
communities attribute string with regular expression. Standard
community list is compiled into binary format when user define it.
Standard community list will be directly compared to BGP communities
attribute in BGP updates. Therefore the comparison is faster than
expanded community list.

.. index:: ip community-list standard NAME permit|deny COMMUNITY

``ip community-list standard NAME permit|deny COMMUNITY``
  This command defines a new standard community list. `community`
  is communities value. The `community` is compiled into community
  structure. We can define multiple community list under same name. In
  that case match will happen user defined order. Once the
  community list matches to communities attribute in BGP updates it
  return permit or deny by the community list definition. When there is
  no matched entry, deny will be returned. When `community` is
  empty it matches to any routes.

.. index:: ip community-list expanded NAME permit|deny LINE

``ip community-list expanded NAME permit|deny LINE``
  This command defines a new expanded community list. `line` is a
  string expression of communities attribute. `line` can be a
  regular expression (:ref:`BGP_Regular_Expressions`) to match
  the communities attribute in BGP updates.

.. index:: no ip community-list NAME

``no ip community-list NAME``
.. index:: no ip community-list standard NAME

``no ip community-list standard NAME``
.. index:: no ip community-list expanded NAME

``no ip community-list expanded NAME``
      These commands delete community lists specified by `name`. All of
      community lists shares a single name space. So community lists can be
      removed simpley specifying community lists name.

.. index:: show ip community-list

``show ip community-list``
.. index:: show ip community-list NAME

``show ip community-list NAME``
  This command displays current community list information. When
  `name` is specified the specified community list's information is
  shown.

::

    # show ip community-list
    Named Community standard list CLIST
  permit 7675:80 7675:100 no-export
  deny internet
    Named Community expanded list EXPAND
  permit :

    # show ip community-list CLIST
    Named Community standard list CLIST
  permit 7675:80 7675:100 no-export
  deny internet


.. _Numbered_BGP_Community_Lists:

Numbered BGP Community Lists
----------------------------

When number is used for BGP community list name, the number has
special meanings. Community list number in the range from 1 and 99 is
standard community list. Community list number in the range from 100
to 199 is expanded community list. These community lists are called
as numbered community lists. On the other hand normal community lists
is called as named community lists.

.. index:: ip community-list <1-99> permit|deny COMMUNITY

``ip community-list <1-99> permit|deny COMMUNITY``
  This command defines a new community list. <1-99> is standard
  community list number. Community list name within this range defines
  standard community list. When `community` is empty it matches to
  any routes.

.. index:: ip community-list <100-199> permit|deny COMMUNITY

``ip community-list <100-199> permit|deny COMMUNITY``
  This command defines a new community list. <100-199> is expanded
  community list number. Community list name within this range defines
  expanded community list.

.. index:: ip community-list NAME permit|deny COMMUNITY

``ip community-list NAME permit|deny COMMUNITY``
  When community list type is not specifed, the community list type is
  automatically detected. If `community` can be compiled into
  communities attribute, the community list is defined as a standard
  community list. Otherwise it is defined as an expanded community
  list. This feature is left for backward compability. Use of this
  feature is not recommended.

.. _BGP_Community_in_Route_Map:

BGP Community in Route Map
--------------------------

In Route Map (:ref:`Route_Map`), we can match or set BGP
communities attribute. Using this feature network operator can
implement their network policy based on BGP communities attribute.

Following commands can be used in Route Map.

.. index:: match community WORD

``match community WORD``
.. index:: match community WORD exact-match

``match community WORD exact-match``
    This command perform match to BGP updates using community list
    `word`. When the one of BGP communities value match to the one of
    communities value in community list, it is match. When
    `exact-match` keyword is spcified, match happen only when BGP
    updates have completely same communities value specified in the
    community list.

.. index:: set community none

``set community none``
.. index:: set community COMMUNITY

``set community COMMUNITY``
.. index:: set community COMMUNITY additive

``set community COMMUNITY additive``
  This command manipulate communities value in BGP updates. When
  `none` is specified as communities value, it removes entire
  communities attribute from BGP updates. When `community` is not
  `none`, specified communities value is set to BGP updates. If
  BGP updates already has BGP communities value, the existing BGP
  communities value is replaced with specified `community` value.
  When `additive` keyword is specified, `community` is appended
  to the existing communities value.

.. index:: set comm-list WORD delete

``set comm-list WORD delete``
  This command remove communities value from BGP communities attribute.
  The `word` is community list name. When BGP route's communities
  value matches to the community list `word`, the communities value
  is removed. When all of communities value is removed eventually, the
  BGP update's communities attribute is completely removed.

.. _Display_BGP_Routes_by_Community:

Display BGP Routes by Community
-------------------------------

To show BGP routes which has specific BGP communities attribute,
`show bgp {ipv4|ipv6}` command can be used. The
`community` and `community-list` subcommand can be used.

.. index:: show bgp ipv4|ipv6 community

``show bgp ipv4|ipv6 community``
.. index:: show bgp ipv4|ipv6 community COMMUNITY

``show bgp ipv4|ipv6 community COMMUNITY``
.. index:: show bgp ipv4|ipv6 community COMMUNITY exact-match

``show bgp ipv4|ipv6 community COMMUNITY exact-match``
      `show bgp {ipv4|ipv6} community` displays BGP routes which has communities
      attribute. Where the address family can be IPv4 or IPv6 among others. When
      `community` is specified, BGP routes that matches `community` value is
      displayed. For this command, `internet` keyword can't be used for
      `community` value. When `exact-match` is specified, it display only
      routes that have an exact match.

.. index:: show bgp ipv4|ipv6 community-list WORD

``show bgp ipv4|ipv6 community-list WORD``
.. index:: show bgp ipv4|ipv6 community-list WORD exact-match

``show bgp ipv4|ipv6 community-list WORD exact-match``
  This commands display BGP routes for the address family specified that matches
  community list `word`. When `exact-match` is specified, display only
  routes that have an exact match.

.. _Using_BGP_Communities_Attribute:

Using BGP Communities Attribute
-------------------------------

Following configuration is the most typical usage of BGP communities
attribute. AS 7675 provides upstream Internet connection to AS 100.
When following configuration exists in AS 7675, AS 100 networks
operator can set local preference in AS 7675 network by setting BGP
communities attribute to the updates.

::

  router bgp 7675
   neighbor 192.168.0.1 remote-as 100
   address-family ipv4 unicast
    neighbor 192.168.0.1 route-map RMAP in
   exit-address-family
  !
  ip community-list 70 permit 7675:70
  ip community-list 70 deny
  ip community-list 80 permit 7675:80
  ip community-list 80 deny
  ip community-list 90 permit 7675:90
  ip community-list 90 deny
  !
  route-map RMAP permit 10
   match community 70
   set local-preference 70
  !
  route-map RMAP permit 20
   match community 80
   set local-preference 80
  !
  route-map RMAP permit 30
   match community 90
   set local-preference 90


Following configuration announce 10.0.0.0/8 from AS 100 to AS 7675.
The route has communities value 7675:80 so when above configuration
exists in AS 7675, announced route's local preference will be set to
value 80.

::

  router bgp 100
   network 10.0.0.0/8
   neighbor 192.168.0.2 remote-as 7675
   address-family ipv4 unicast
    neighbor 192.168.0.2 route-map RMAP out
   exit-address-family
  !
  ip prefix-list PLIST permit 10.0.0.0/8
  !
  route-map RMAP permit 10
   match ip address prefix-list PLIST
   set community 7675:80


Following configuration is an example of BGP route filtering using
communities attribute. This configuration only permit BGP routes
which has BGP communities value 0:80 or 0:90. Network operator can
put special internal communities value at BGP border router, then
limit the BGP routes announcement into the internal network.

::

  router bgp 7675
   neighbor 192.168.0.1 remote-as 100
   address-family ipv4 unicast
    neighbor 192.168.0.1 route-map RMAP in
   exit-address-family
  !
  ip community-list 1 permit 0:80 0:90
  !
  route-map RMAP permit in
   match community 1


Following exmaple filter BGP routes which has communities value 1:1.
When there is no match community-list returns deny. To avoid
filtering all of routes, we need to define permit any at last.

::

  router bgp 7675
   neighbor 192.168.0.1 remote-as 100
   address-family ipv4 unicast
    neighbor 192.168.0.1 route-map RMAP in
   exit-address-family
  !
  ip community-list standard FILTER deny 1:1
  ip community-list standard FILTER permit
  !
  route-map RMAP permit 10
   match community FILTER


Communities value keyword `internet` has special meanings in
standard community lists. In below example `internet` act as
match any. It matches all of BGP routes even if the route does not
have communities attribute at all. So community list `INTERNET`
is same as above example's `FILTER`.

::

  ip community-list standard INTERNET deny 1:1
  ip community-list standard INTERNET permit internet


Following configuration is an example of communities value deletion.
With this configuration communities value 100:1 and 100:2 is removed
from BGP updates. For communities value deletion, only `permit`
community-list is used. `deny` community-list is ignored.

::

  router bgp 7675
   neighbor 192.168.0.1 remote-as 100
   address-family ipv4 unicast
    neighbor 192.168.0.1 route-map RMAP in
   exit-address-family
  !
  ip community-list standard DEL permit 100:1 100:2
  !
  route-map RMAP permit 10
   set comm-list DEL delete


.. _BGP_Extended_Communities_Attribute:

BGP Extended Communities Attribute
==================================

BGP extended communities attribute is introduced with MPLS VPN/BGP
technology. MPLS VPN/BGP expands capability of network infrastructure
to provide VPN functionality. At the same time it requires a new
framework for policy routing. With BGP Extended Communities Attribute
we can use Route Target or Site of Origin for implementing network
policy for MPLS VPN/BGP.

BGP Extended Communities Attribute is similar to BGP Communities
Attribute. It is an optional transitive attribute. BGP Extended
Communities Attribute can carry multiple Extended Community value.
Each Extended Community value is eight octet length.

BGP Extended Communities Attribute provides an extended range
compared with BGP Communities Attribute. Adding to that there is a
type field in each value to provides community space structure.

There are two format to define Extended Community value. One is AS
based format the other is IP address based format.



*AS:VAL*
  This is a format to define AS based Extended Community value.
  `AS` part is 2 octets Global Administrator subfield in Extended
  Community value. `VAL` part is 4 octets Local Administrator
  subfield. `7675:100` represents AS 7675 policy value 100.

*IP-Address:VAL*
  This is a format to define IP address based Extended Community value.
  `IP-Address` part is 4 octets Global Administrator subfield.
  `VAL` part is 2 octets Local Administrator subfield.
  `10.0.0.1:100` represents

.. _BGP_Extended_Community_Lists:

BGP Extended Community Lists
----------------------------

Expanded Community Lists is a user defined BGP Expanded Community
Lists.

.. index:: ip extcommunity-list standard NAME permit|deny EXTCOMMUNITY

``ip extcommunity-list standard NAME permit|deny EXTCOMMUNITY``
  This command defines a new standard extcommunity-list.
  `extcommunity` is extended communities value. The
  `extcommunity` is compiled into extended community structure. We
  can define multiple extcommunity-list under same name. In that case
  match will happen user defined order. Once the extcommunity-list
  matches to extended communities attribute in BGP updates it return
  permit or deny based upon the extcommunity-list definition. When
  there is no matched entry, deny will be returned. When
  `extcommunity` is empty it matches to any routes.

.. index:: ip extcommunity-list expanded NAME permit|deny LINE

``ip extcommunity-list expanded NAME permit|deny LINE``
  This command defines a new expanded extcommunity-list. `line` is
  a string expression of extended communities attribute. `line` can
  be a regular expression (:ref:`BGP_Regular_Expressions`) to match an
  extended communities attribute in BGP updates.

.. index:: no ip extcommunity-list NAME

``no ip extcommunity-list NAME``
.. index:: no ip extcommunity-list standard NAME

``no ip extcommunity-list standard NAME``
.. index:: no ip extcommunity-list expanded NAME

``no ip extcommunity-list expanded NAME``
      These commands delete extended community lists specified by
      `name`. All of extended community lists shares a single name
      space. So extended community lists can be removed simpley specifying
      the name.

.. index:: show ip extcommunity-list

``show ip extcommunity-list``
.. index:: show ip extcommunity-list NAME

``show ip extcommunity-list NAME``
  This command displays current extcommunity-list information. When
  `name` is specified the community list's information is shown.

::

    # show ip extcommunity-list


.. _BGP_Extended_Communities_in_Route_Map:

BGP Extended Communities in Route Map
-------------------------------------

.. index:: match extcommunity WORD

``match extcommunity WORD``

.. index:: set extcommunity rt EXTCOMMUNITY

``set extcommunity rt EXTCOMMUNITY``
  This command set Route Target value.

.. index:: set extcommunity soo EXTCOMMUNITY

``set extcommunity soo EXTCOMMUNITY``
  This command set Site of Origin value.

.. _BGP_Large_Communities_Attribute:

BGP Large Communities Attribute
===============================

The BGP Large Communities attribute was introduced in Feb 2017 with
:t:`RFC8092, BGP Large Communities Attribute`.

The BGP Large Communities Attribute is similar to the BGP Communities
Attribute except that it has 3 components instead of two and each of
which are 4 octets in length. Large Communities bring additional
functionality and convenience over traditional communities, specifically
the fact that the `GLOBAL` part below is now 4 octets wide allowing
AS4 operators seamless use.



*GLOBAL:LOCAL1:LOCAL2*
  This is the format to define Large Community values. Referencing
  :t:`RFC8195, Use of BGP Large Communities` the values are commonly
  referred to as follows.
  The `GLOBAL` part is a 4 octet Global Administrator field, common
  use of this field is the operators AS number.
  The `LOCAL1` part is a 4 octet Local Data Part 1 subfield referred
  to as a function.
  The `LOCAL2` part is a 4 octet Local Data Part 2 field and referred
  to as the parameter subfield. `65551:1:10` represents AS 65551
  function 1 and parameter 10.
  The referenced RFC above gives some guidelines on recommended usage.

.. _BGP_Large_Community_Lists:

BGP Large Community Lists
-------------------------

Two types of large community lists are supported, namely `standard` and
`expanded`.

.. index:: ip large-community-list standard NAME permit|deny LARGE-COMMUNITY

``ip large-community-list standard NAME permit|deny LARGE-COMMUNITY``
  This command defines a new standard large-community-list.
  `large-community` is the Large Community value. We
  can add multiple large communities under same name. In that case
  the match will happen in the user defined order. Once the large-community-list
  matches the Large Communities attribute in BGP updates it will return
  permit or deny based upon the large-community-list definition. When
  there is no matched entry, a deny will be returned. When `large-community`
  is empty it matches any routes.

.. index:: ip large-community-list expanded NAME permit|deny LINE

``ip large-community-list expanded NAME permit|deny LINE``
  This command defines a new expanded large-community-list. Where `line` is
  a string matching expression, it will be compared to the entire Large Communities
  attribute as a string, with each large-community in order from lowest to highest.
  `line` can also be a regular expression which matches this Large
  Community attribute.

.. index:: no ip large-community-list NAME

``no ip large-community-list NAME``
.. index:: no ip large-community-list standard NAME

``no ip large-community-list standard NAME``
.. index:: no ip large-community-list expanded NAME

``no ip large-community-list expanded NAME``
      These commands delete Large Community lists specified by
      `name`. All Large Community lists share a single namespace.
      This means Large Community lists can be removed by simply specifying the name.

.. index:: show ip large-community-list

``show ip large-community-list``
.. index:: show ip large-community-list NAME

``show ip large-community-list NAME``
  This command display current large-community-list information. When
  `name` is specified the community list information is shown.

.. index:: show ip bgp large-community-info

``show ip bgp large-community-info``
  This command displays the current large communities in use.

.. _BGP_Large_Communities_in_Route_Map:

BGP Large Communities in Route Map
----------------------------------

.. index:: match large-community LINE

``match large-community LINE``
  Where `line` can be a simple string to match, or a regular expression.
  It is very important to note that this match occurs on the entire
  large-community string as a whole, where each large-community is ordered
  from lowest to highest.

.. index:: set large-community LARGE-COMMUNITY

``set large-community LARGE-COMMUNITY``
.. index:: set large-community LARGE-COMMUNITY LARGE-COMMUNITY

``set large-community LARGE-COMMUNITY LARGE-COMMUNITY``
.. index:: set large-community LARGE-COMMUNITY additive

``set large-community LARGE-COMMUNITY additive``
      These commands are used for setting large-community values. The first
      command will overwrite any large-communities currently present.
      The second specifies two large-communities, which overwrites the current
      large-community list. The third will add a large-community value without
      overwriting other values. Multiple large-community values can be specified.

.. _Displaying_BGP_information:

Displaying BGP information
==========================


.. _Showing_BGP_information:

Showing BGP information
-----------------------

.. index:: show ip bgp

``show ip bgp``
.. index:: show ip bgp A.B.C.D

``show ip bgp A.B.C.D``
.. index:: show ip bgp X:X::X:X

``show ip bgp X:X::X:X``
      This command displays BGP routes. When no route is specified it
      display all of IPv4 BGP routes.

::

      BGP table version is 0, local router ID is 10.1.1.1
      Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
      Origin codes: i - IGP, e - EGP, ? - incomplete

   Network    Next Hop      Metric LocPrf Weight Path
      *> 1.1.1.1/32       0.0.0.0      0   32768 i

      Total number of prefixes 1


.. index:: show ip bgp regexp LINE

``show ip bgp regexp LINE``
      This command displays BGP routes using AS path regular expression
      (:ref:`BGP_Regular_Expressions`).

.. index:: show ip bgp community COMMUNITY

``show ip bgp community COMMUNITY``
.. index:: show ip bgp community COMMUNITY exact-match

``show ip bgp community COMMUNITY exact-match``
  This command displays BGP routes using `community` (:ref:`Display_BGP_Routes_by_Community`).

.. index:: show ip bgp community-list WORD

``show ip bgp community-list WORD``
.. index:: show ip bgp community-list WORD exact-match

``show ip bgp community-list WORD exact-match``
    This command displays BGP routes using community list (:ref:`Display_BGP_Routes_by_Community`).

.. index:: show bgp ipv4|ipv6 summary

``show bgp ipv4|ipv6 summary``
    Show a bgp peer summary for the specified address family.

.. index:: show bgp ipv4|ipv6 neighbor [PEER]

``show bgp ipv4|ipv6 neighbor [PEER]``
    This command shows information on a specific BGP `peer`.

.. index:: show bgp ipv4|ipv6 dampening dampened-paths

``show bgp ipv4|ipv6 dampening dampened-paths``
    Display paths suppressed due to dampening.

.. index:: show bgp ipv4|ipv6 dampening flap-statistics

``show bgp ipv4|ipv6 dampening flap-statistics``
    Display flap statistics of routes.

.. _Other_BGP_commands:

Other BGP commands
------------------

.. index:: clear bgp ipv4|ipv6 \*

``clear bgp ipv4|ipv6 \*``
  Clear all address family peers.

.. index:: clear bgp ipv4|ipv6 PEER

``clear bgp ipv4|ipv6 PEER``
  Clear peers which have addresses of X.X.X.X

.. index:: clear bgp ipv4|ipv6 PEER soft in

``clear bgp ipv4|ipv6 PEER soft in``
  Clear peer using soft reconfiguration.

.. index:: show debug

``show debug``
.. index:: debug event

``debug event``
.. index:: debug update

``debug update``
.. index:: debug keepalive

``debug keepalive``
.. index:: no debug event

``no debug event``
.. index:: no debug update

``no debug update``
.. index:: no debug keepalive

``no debug keepalive``

.. _Capability_Negotiation:

Capability Negotiation
======================

When adding IPv6 routing information exchange feature to BGP. There
were some proposals. :abbr:`IETF (Internet Engineering Task Force)`
:abbr:`IDR ( Inter Domain Routing)` :abbr:`IDR ( Inter Domain Routing)` adopted
a proposal called Multiprotocol Extension for BGP. The specification
is described in :rfc:`2283`. The protocol does not define new protocols.
It defines new attributes to existing BGP. When it is used exchanging
IPv6 routing information it is called BGP-4+. When it is used for
exchanging multicast routing information it is called MBGP.

*bgpd* supports Multiprotocol Extension for BGP. So if remote
peer supports the protocol, *bgpd* can exchange IPv6 and/or
multicast routing information.

Traditional BGP did not have the feature to detect remote peer's
capabilities, e.g. whether it can handle prefix types other than IPv4
unicast routes. This was a big problem using Multiprotocol Extension
for BGP to operational network. @cite{RFC2842, Capabilities
Advertisement with BGP-4} adopted a feature called Capability
Negotiation. *bgpd* use this Capability Negotiation to detect
the remote peer's capabilities. If the peer is only configured as IPv4
unicast neighbor, *bgpd* does not send these Capability
Negotiation packets (at least not unless other optional BGP features
require capability negotation).

By default, FRR will bring up peering with minimal common capability
for the both sides. For example, local router has unicast and
multicast capabilitie and remote router has unicast capability. In
this case, the local router will establish the connection with unicast
only capability. When there are no common capabilities, FRR sends
Unsupported Capability error and then resets the connection.

If you want to completely match capabilities with remote peer. Please
use *strict-capability-match* command.

.. index:: neighbor `peer` strict-capability-match

``neighbor `peer` strict-capability-match``

.. index:: no neighbor `peer` strict-capability-match

``no neighbor `peer` strict-capability-match``

    Strictly compares remote capabilities and local capabilities. If capabilities
    are different, send Unsupported Capability error then reset connection.

  You may want to disable sending Capability Negotiation OPEN message
  optional parameter to the peer when remote peer does not implement
  Capability Negotiation. Please use *dont-capability-negotiate*
  command to disable the feature.

.. index:: neighbor `peer` dont-capability-negotiate

``neighbor `peer` dont-capability-negotiate``

.. index:: no neighbor `peer` dont-capability-negotiate

``no neighbor `peer` dont-capability-negotiate``

      Suppress sending Capability Negotiation as OPEN message optional
      parameter to the peer. This command only affects the peer is configured
      other than IPv4 unicast configuration.

    When remote peer does not have capability negotiation feature, remote
    peer will not send any capabilities at all. In that case, bgp
    configures the peer with configured capabilities.

    You may prefer locally configured capabilities more than the negotiated
    capabilities even though remote peer sends capabilities. If the peer
    is configured by *override-capability*, *bgpd* ignores
    received capabilities then override negotiated capabilities with
    configured values.

.. index:: neighbor `peer` override-capability

``neighbor `peer` override-capability``

.. index:: no neighbor `peer` override-capability

``no neighbor `peer` override-capability``

  Override the result of Capability Negotiation with local configuration.
  Ignore remote peer's capability value.

.. _Route_Reflector:

Route Reflector
===============

.. index:: bgp cluster-id `a.b.c.d`

``bgp cluster-id `a.b.c.d```


.. index:: neighbor `peer` route-reflector-client

``neighbor `peer` route-reflector-client``

.. index:: no neighbor `peer` route-reflector-client

``no neighbor `peer` route-reflector-client``


.. _Route_Server:

Route Server
============

At an Internet Exchange point, many ISPs are connected to each other by
external BGP peering. Normally these external BGP connection are done by
``full mesh`` method. As with internal BGP full mesh formation,
this method has a scaling problem.

This scaling problem is well known. Route Server is a method to resolve
the problem. Each ISP's BGP router only peers to Route Server. Route
Server serves as BGP information exchange to other BGP routers. By
applying this method, numbers of BGP connections is reduced from
O(n*(n-1)/2) to O(n).

Unlike normal BGP router, Route Server must have several routing tables
for managing different routing policies for each BGP speaker. We call the
routing tables as different ``view`` s. *bgpd* can work as
normal BGP router or Route Server or both at the same time.

.. _Multiple_instance:

Multiple instance
-----------------

To enable multiple view function of `bgpd`, you must turn on
multiple instance feature beforehand.

.. index:: bgp multiple-instance

``bgp multiple-instance``
  Enable BGP multiple instance feature. After this feature is enabled,
  you can make multiple BGP instances or multiple BGP views.

.. index:: no bgp multiple-instance

``no bgp multiple-instance``
  Disable BGP multiple instance feature. You can not disable this feature
  when BGP multiple instances or views exist.

When you want to make configuration more Cisco like one,

.. index:: bgp config-type cisco

``bgp config-type cisco``
  Cisco compatible BGP configuration output.

When bgp config-type cisco is specified,

'no synchronization' is displayed.
'no auto-summary' is displayed.

'network' and 'aggregate-address' argument is displayed as
'A.B.C.D M.M.M.M'

FRR: network 10.0.0.0/8
Cisco: network 10.0.0.0

FRR: aggregate-address 192.168.0.0/24
Cisco: aggregate-address 192.168.0.0 255.255.255.0

Community attribute handling is also different. If there is no
configuration is specified community attribute and extended community
attribute are sent to neighbor. When user manually disable the
feature community attribute is not sent to the neighbor. In case of
*bgp config-type cisco* is specified, community attribute is not
sent to the neighbor by default. To send community attribute user has
to specify *neighbor A.B.C.D send-community* command.

::

  !
  router bgp 1
   neighbor 10.0.0.1 remote-as 1
   address-family ipv4 unicast
    no neighbor 10.0.0.1 send-community
   exit-address-family
  !
  router bgp 1
   neighbor 10.0.0.1 remote-as 1
   address-family ipv4 unicast
    neighbor 10.0.0.1 send-community
   exit-address-family
  !


.. index:: bgp config-type zebra

``bgp config-type zebra``
  FRR style BGP configuration. This is default.

.. _BGP_instance_and_view:

BGP instance and view
---------------------

BGP instance is a normal BGP process. The result of route selection
goes to the kernel routing table. You can setup different AS at the
same time when BGP multiple instance feature is enabled.

.. index:: router bgp AS-NUMBER

``router bgp AS-NUMBER``
  Make a new BGP instance. You can use arbitrary word for the `name`.

::

  bgp multiple-instance
  !
  router bgp 1
   neighbor 10.0.0.1 remote-as 2
   neighbor 10.0.0.2 remote-as 3
  !
  router bgp 2
   neighbor 10.0.0.3 remote-as 4
   neighbor 10.0.0.4 remote-as 5


BGP view is almost same as normal BGP process. The result of
route selection does not go to the kernel routing table. BGP view is
only for exchanging BGP routing information.

.. index:: router bgp AS-NUMBER view NAME

``router bgp AS-NUMBER view NAME``
  Make a new BGP view. You can use arbitrary word for the `name`. This
  view's route selection result does not go to the kernel routing table.

With this command, you can setup Route Server like below.

::

  bgp multiple-instance
  !
  router bgp 1 view 1
   neighbor 10.0.0.1 remote-as 2
   neighbor 10.0.0.2 remote-as 3
  !
  router bgp 2 view 2
   neighbor 10.0.0.3 remote-as 4
   neighbor 10.0.0.4 remote-as 5


.. _Routing_policy:

Routing policy
--------------

You can set different routing policy for a peer. For example, you can
set different filter for a peer.

::

  bgp multiple-instance
  !
  router bgp 1 view 1
   neighbor 10.0.0.1 remote-as 2
   address-family ipv4 unicast
    neighbor 10.0.0.1 distribute-list 1 in
   exit-address-family
  !
  router bgp 1 view 2
   neighbor 10.0.0.1 remote-as 2
   address-family ipv4 unicast
    neighbor 10.0.0.1 distribute-list 2 in
   exit-address-family


This means BGP update from a peer 10.0.0.1 goes to both BGP view 1 and view
2. When the update is inserted into view 1, distribute-list 1 is
applied. On the other hand, when the update is inserted into view 2,
distribute-list 2 is applied.

.. _Viewing_the_view:

Viewing the view
----------------

To display routing table of BGP view, you must specify view name.

.. index:: show ip bgp view NAME

``show ip bgp view NAME``
  Display routing table of BGP view `name`.

.. _BGP_Regular_Expressions:

BGP Regular Expressions
=======================

BGP regular expressions are based on `POSIX 1003.2` regular
expressions. The following description is just a quick subset of the
`POSIX` regular expressions. Adding to that, the special character
'_' is added.



*.*
  Matches any single character.

*
  Matches 0 or more occurrences of pattern.

+
  Matches 1 or more occurrences of pattern.

?
  Match 0 or 1 occurrences of pattern.

^
  Matches the beginning of the line.

$
  Matches the end of the line.

_
  Character `_` has special meanings in BGP regular expressions.
  It matches to space and comma , and AS set delimiter { and } and AS
  confederation delimiter `(` and `)`. And it also matches to
  the beginning of the line and the end of the line. So `_` can be
  used for AS value boundaries match. This character technically evaluates
  to `(^|[,{}() ]|$)`.

.. _How_to_set_up_a_6-Bone_connection:

How to set up a 6-Bone connection
=================================

::

  zebra configuration
  ===================
  !
  ! Actually there is no need to configure zebra
  !

  bgpd configuration
  ==================
  !
  ! This means that routes go through zebra and into the kernel.
  !
  router zebra
  !
  ! MP-BGP configuration
  !
  router bgp 7675
   bgp router-id 10.0.0.1
   neighbor 3ffe:1cfa:0:2:2a0:c9ff:fe9e:f56 remote-as `as-number`
  !
   address-family ipv6
   network 3ffe:506::/32
   neighbor 3ffe:1cfa:0:2:2a0:c9ff:fe9e:f56 activate
   neighbor 3ffe:1cfa:0:2:2a0:c9ff:fe9e:f56 route-map set-nexthop out
   neighbor 3ffe:1cfa:0:2:2c0:4fff:fe68:a231 remote-as `as-number`
   neighbor 3ffe:1cfa:0:2:2c0:4fff:fe68:a231 route-map set-nexthop out
   exit-address-family
  !
  ipv6 access-list all permit any
  !
  ! Set output nexthop address.
  !
  route-map set-nexthop permit 10
   match ipv6 address all
   set ipv6 nexthop global 3ffe:1cfa:0:2:2c0:4fff:fe68:a225
   set ipv6 nexthop local fe80::2c0:4fff:fe68:a225
  !
  ! logfile FILENAME is obsolete. Please use log file FILENAME

  log file bgpd.log
  !


.. _Dump_BGP_packets_and_table:

Dump BGP packets and table
==========================

.. index:: dump bgp all PATH [INTERVAL]

``dump bgp all PATH [INTERVAL]``
.. index:: dump bgp all-et PATH [INTERVAL]

``dump bgp all-et PATH [INTERVAL]``
.. index:: no dump bgp all [PATH] [INTERVAL]

``no dump bgp all [PATH] [INTERVAL]``
      Dump all BGP packet and events to `path` file.
      If `interval` is set, a new file will be created for echo `interval` of seconds.
      The path `path` can be set with date and time formatting (strftime).
      The type ‘all-et’ enables support for Extended Timestamp Header (:ref:`Packet_Binary_Dump_Format`).
      (:ref:`Packet_Binary_Dump_Format`)

.. index:: dump bgp updates PATH [INTERVAL]

``dump bgp updates PATH [INTERVAL]``
.. index:: dump bgp updates-et PATH [INTERVAL]

``dump bgp updates-et PATH [INTERVAL]``
.. index:: no dump bgp updates [PATH] [INTERVAL]

``no dump bgp updates [PATH] [INTERVAL]``
    Dump only BGP updates messages to `path` file.
    If `interval` is set, a new file will be created for echo `interval` of seconds.
    The path `path` can be set with date and time formatting (strftime).
    The type ‘updates-et’ enables support for Extended Timestamp Header (:ref:`Packet_Binary_Dump_Format`).

.. index:: dump bgp routes-mrt PATH

``dump bgp routes-mrt PATH``
.. index:: dump bgp routes-mrt PATH INTERVAL

``dump bgp routes-mrt PATH INTERVAL``
.. index:: no dump bgp route-mrt [PATH] [INTERVAL]

``no dump bgp route-mrt [PATH] [INTERVAL]``
  Dump whole BGP routing table to `path`. This is heavy process.
  The path `path` can be set with date and time formatting (strftime).
  If `interval` is set, a new file will be created for echo `interval` of seconds.

      Note: the interval variable can also be set using hours and minutes: 04h20m00.

BGP Configuration Examples
==========================

Example of a session to an upstream, advertising only one prefix to it.

::

  router bgp 64512
   bgp router-id 10.236.87.1
   neighbor upstream peer-group
   neighbor upstream remote-as 64515
   neighbor upstream capability dynamic
   neighbor 10.1.1.1 peer-group upstream
   neighbor 10.1.1.1 description ACME ISP

   address-family ipv4 unicast
    network 10.236.87.0/24
    neighbor upstream prefix-list pl-allowed-adv out
   exit-address-family
  !
  ip prefix-list pl-allowed-adv seq 5 permit 82.195.133.0/25
  ip prefix-list pl-allowed-adv seq 10 deny any



A more complex example. With upstream, peer and customer sessions.
Advertising global prefixes and NO_EXPORT prefixes and providing
actions for customer routes based on community values. Extensive use of
route-maps and the 'call' feature to support selective advertising of
prefixes. This example is intended as guidance only, it has NOT been
tested and almost certainly containts silly mistakes, if not serious
flaws.

::

  router bgp 64512
   bgp router-id 10.236.87.1
   neighbor upstream capability dynamic
   neighbor cust capability dynamic
   neighbor peer capability dynamic
   neighbor 10.1.1.1 remote-as 64515
   neighbor 10.1.1.1 peer-group upstream
   neighbor 10.2.1.1 remote-as 64516
   neighbor 10.2.1.1 peer-group upstream
   neighbor 10.3.1.1 remote-as 64517
   neighbor 10.3.1.1 peer-group cust-default
   neighbor 10.3.1.1 description customer1
   neighbor 10.4.1.1 remote-as 64518
   neighbor 10.4.1.1 peer-group cust
   neighbor 10.4.1.1 description customer2
   neighbor 10.5.1.1 remote-as 64519
   neighbor 10.5.1.1 peer-group peer
   neighbor 10.5.1.1 description peer AS 1
   neighbor 10.6.1.1 remote-as 64520
   neighbor 10.6.1.1 peer-group peer
   neighbor 10.6.1.1 description peer AS 2

   address-family ipv4 unicast
    network 10.123.456.0/24
    network 10.123.456.128/25 route-map rm-no-export
    neighbor upstream route-map rm-upstream-out out
    neighbor cust route-map rm-cust-in in
    neighbor cust route-map rm-cust-out out
    neighbor cust send-community both
    neighbor peer route-map rm-peer-in in
    neighbor peer route-map rm-peer-out out
    neighbor peer send-community both
    neighbor 10.3.1.1 prefix-list pl-cust1-network in
    neighbor 10.4.1.1 prefix-list pl-cust2-network in
    neighbor 10.5.1.1 prefix-list pl-peer1-network in
    neighbor 10.6.1.1 prefix-list pl-peer2-network in
   exit-address-family
  !
  ip prefix-list pl-default permit 0.0.0.0/0
  !
  ip prefix-list pl-upstream-peers permit 10.1.1.1/32
  ip prefix-list pl-upstream-peers permit 10.2.1.1/32
  !
  ip prefix-list pl-cust1-network permit 10.3.1.0/24
  ip prefix-list pl-cust1-network permit 10.3.2.0/24
  !
  ip prefix-list pl-cust2-network permit 10.4.1.0/24
  !
  ip prefix-list pl-peer1-network permit 10.5.1.0/24
  ip prefix-list pl-peer1-network permit 10.5.2.0/24
  ip prefix-list pl-peer1-network permit 192.168.0.0/24
  !
  ip prefix-list pl-peer2-network permit 10.6.1.0/24
  ip prefix-list pl-peer2-network permit 10.6.2.0/24
  ip prefix-list pl-peer2-network permit 192.168.1.0/24
  ip prefix-list pl-peer2-network permit 192.168.2.0/24
  ip prefix-list pl-peer2-network permit 172.16.1/24
  !
  ip as-path access-list asp-own-as permit ^$
  ip as-path access-list asp-own-as permit _64512_
  !
  ! #################################################################
  ! Match communities we provide actions for, on routes receives from
  ! customers. Communities values of <our-ASN>:X, with X, have actions:
  !
  ! 100 - blackhole the prefix
  ! 200 - set no_export
  ! 300 - advertise only to other customers
  ! 400 - advertise only to upstreams
  ! 500 - set no_export when advertising to upstreams
  ! 2X00 - set local_preference to X00
  !
  ! blackhole the prefix of the route
  ip community-list standard cm-blackhole permit 64512:100
  !
  ! set no-export community before advertising
  ip community-list standard cm-set-no-export permit 64512:200
  !
  ! advertise only to other customers
  ip community-list standard cm-cust-only permit 64512:300
  !
  ! advertise only to upstreams
  ip community-list standard cm-upstream-only permit 64512:400
  !
  ! advertise to upstreams with no-export
  ip community-list standard cm-upstream-noexport permit 64512:500
  !
  ! set local-pref to least significant 3 digits of the community
  ip community-list standard cm-prefmod-100 permit 64512:2100
  ip community-list standard cm-prefmod-200 permit 64512:2200
  ip community-list standard cm-prefmod-300 permit 64512:2300
  ip community-list standard cm-prefmod-400 permit 64512:2400
  ip community-list expanded cme-prefmod-range permit 64512:2...
  !
  ! Informational communities
  !
  ! 3000 - learned from upstream
  ! 3100 - learned from customer
  ! 3200 - learned from peer
  !
  ip community-list standard cm-learnt-upstream permit 64512:3000
  ip community-list standard cm-learnt-cust permit 64512:3100
  ip community-list standard cm-learnt-peer permit 64512:3200
  !
  ! ###################################################################
  ! Utility route-maps
  !
  ! These utility route-maps generally should not used to permit/deny
  ! routes, i.e. they do not have meaning as filters, and hence probably
  ! should be used with 'on-match next'. These all finish with an empty
  ! permit entry so as not interfere with processing in the caller.
  !
  route-map rm-no-export permit 10
   set community additive no-export
  route-map rm-no-export permit 20
  !
  route-map rm-blackhole permit 10
   description blackhole, up-pref and ensure it cant escape this AS
   set ip next-hop 127.0.0.1
   set local-preference 10
   set community additive no-export
  route-map rm-blackhole permit 20
  !
  ! Set local-pref as requested
  route-map rm-prefmod permit 10
   match community cm-prefmod-100
   set local-preference 100
  route-map rm-prefmod permit 20
   match community cm-prefmod-200
   set local-preference 200
  route-map rm-prefmod permit 30
   match community cm-prefmod-300
   set local-preference 300
  route-map rm-prefmod permit 40
   match community cm-prefmod-400
   set local-preference 400
  route-map rm-prefmod permit 50
  !
  ! Community actions to take on receipt of route.
  route-map rm-community-in permit 10
   description check for blackholing, no point continuing if it matches.
   match community cm-blackhole
   call rm-blackhole
  route-map rm-community-in permit 20
   match community cm-set-no-export
   call rm-no-export
   on-match next
  route-map rm-community-in permit 30
   match community cme-prefmod-range
   call rm-prefmod
  route-map rm-community-in permit 40
  !
  ! #####################################################################
  ! Community actions to take when advertising a route.
  ! These are filtering route-maps,
  !
  ! Deny customer routes to upstream with cust-only set.
  route-map rm-community-filt-to-upstream deny 10
   match community cm-learnt-cust
   match community cm-cust-only
  route-map rm-community-filt-to-upstream permit 20
  !
  ! Deny customer routes to other customers with upstream-only set.
  route-map rm-community-filt-to-cust deny 10
   match community cm-learnt-cust
   match community cm-upstream-only
  route-map rm-community-filt-to-cust permit 20
  !
  ! ###################################################################
  ! The top-level route-maps applied to sessions. Further entries could
  ! be added obviously..
  !
  ! Customers
  route-map rm-cust-in permit 10
   call rm-community-in
   on-match next
  route-map rm-cust-in permit 20
   set community additive 64512:3100
  route-map rm-cust-in permit 30
  !
  route-map rm-cust-out permit 10
   call rm-community-filt-to-cust
   on-match next
  route-map rm-cust-out permit 20
  !
  ! Upstream transit ASes
  route-map rm-upstream-out permit 10
   description filter customer prefixes which are marked cust-only
   call rm-community-filt-to-upstream
   on-match next
  route-map rm-upstream-out permit 20
   description only customer routes are provided to upstreams/peers
   match community cm-learnt-cust
  !
  ! Peer ASes
  ! outbound policy is same as for upstream
  route-map rm-peer-out permit 10
   call rm-upstream-out
  !
  route-map rm-peer-in permit 10
   set community additive 64512:3200


.. _Configuring_FRR_as_a_Route_Server:

Configuring FRR as a Route Server
=================================

The purpose of a Route Server is to centralize the peerings between BGP
speakers. For example if we have an exchange point scenario with four BGP
speakers, each of which maintaining a BGP peering with the other three
(:ref:`fig:full-mesh`), we can convert it into a centralized scenario where
each of the four establishes a single BGP peering against the Route Server
(:ref:`fig:route-server`).

We will first describe briefly the Route Server model implemented by FRR.
We will explain the commands that have been added for configuring that
model. And finally we will show a full example of FRR configured as Route
Server.

.. include:: rpki.rst