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doc: Add documentation for IANA well-known communities

Coded as part of #2684 and most code written while participating at
BornHack@2018.

bgp.rst: Explain what the communities does and a summarized edition of
the communities purpose.

Signed-off-by: Christoffer <netravnen@gmail.com>
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Christoffer
Christoffer committed Aug 22, 2018
1 parent 9b8c390 commit cae770d31d306e5053c1c69509c03d11903217fa
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  1. +74 −0 doc/user/bgp.rst
@@ -1011,6 +1011,75 @@ is 4 octet long. The following format is used to define the community value.
``internet``
``internet`` represents well-known communities value 0.

``graceful-shutdown``
``graceful-shutdown`` represents well-known communities value
``GRACEFUL_SHUTDOWN`` ``0xFFFF0000`` ``65535:0``. :rfc:`8326` implements
the purpose Graceful BGP Session Shutdown to reduce the amount of
lost traffic when taking BGP sessions down for maintainance. The use
of the community needs to be supported from your peers side to
actually have any effect.

``accept-own``
``accept-own`` represents well-known communities value ``ACCEPT_OWN``
``0xFFFF0001`` ``65535:1``. :rfc:`7611` implements a way to signal
to a router to accept routes with a local nexthop address. This
can be the case when doing policing and having traffic having a
nexthop located in another VRF but still local interface to the
router. It is recommended to read the RFC for full details.

``route-filter-translated-v4``
``route-filter-translated-v4`` represents well-known communities value
``ROUTE_FILTER_TRANSLATED_v4`` ``0xFFFF0002`` ``65535:2``.

``route-filter-v4``
``route-filter-v4`` represents well-known communities value
``ROUTE_FILTER_v4`` ``0xFFFF0003`` ``65535:3``.

``route-filter-translated-v6``
``route-filter-translated-v6`` represents well-known communities value
``ROUTE_FILTER_TRANSLATED_v6`` ``0xFFFF0004`` ``65535:4``.

``route-filter-v6``
``route-filter-v6`` represents well-known communities value
``ROUTE_FILTER_v6`` ``0xFFFF0005`` ``65535:5``.

``llgr-stale``
``llgr-stale`` represents well-known communities value ``LLGR_STALE``
``0xFFFF0006`` ``65535:6``.
Assigned and intented only for use with routers supporting the
Long-lived Graceful Restart Capability as described in
:rfc:`draft-uttaro-idr-bgp-persistence`.
Routers recieving routes with this community may (depending on
implementation) choose allow to reject or modify routes on the
presence or absence of this community.

``no-llgr``
``no-llgr`` represents well-known communities value ``NO_LLGR``
``0xFFFF0007`` ``65535:7``.
Assigned and intented only for use with routers supporting the
Long-lived Graceful Restart Capability as described in
:rfc:`draft-uttaro-idr-bgp-persistence`.
Routers recieving routes with this community may (depending on
implementation) choose allow to reject or modify routes on the
presence or absence of this community.

``accept-own-nexthop``
``accept-own-nexthop`` represents well-known communities value
``accept-own-nexthop`` ``0xFFFF0008`` ``65535:8``.
:rfc:`draft-agrewal-idr-accept-own-nexthop` describes
how to tag and label VPN routes to be able to send traffic between VRFs
via an internal layer 2 domain on the same PE device. Refer to
:rfc:`draft-agrewal-idr-accept-own-nexthop` for full details.

``blackhole``
``blackhole`` represents well-known communities value ``BLACKHOLE``
``0xFFFF029A`` ``65535:666``. :rfc:`7999` documents sending prefixes to
EBGP peers and upstream for the purpose of blackholing traffic.
Prefixes tagged with the this community should normally not be
re-advertised from neighbors of the originating network. It is
recommended upon receiving prefixes tagged with this community to
add ``NO_EXPORT`` and ``NO_ADVERTISE``.

``no-export``
``no-export`` represents well-known communities value ``NO_EXPORT``
``0xFFFFFF01``. All routes carry this value must not be advertised to
@@ -1030,6 +1099,11 @@ is 4 octet long. The following format is used to define the community value.
it is considered as external BGP peer, so the route will not be announced to
the peer.

``no-peer``
``no-peer`` represents well-known communities value ``NOPEER``
``0xFFFFFF04`` ``65535:65284``. :rfc:`3765` is used to communicate to
another network how the originating network want the prefix propagated.

When the communities attribute is received duplicate community values in the
attribute are ignored and value is sorted in numerical order.

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