Pakistan IE Route Server Action BGP Communities

Peeringservices_Team Updated by Peeringservices_Team

Action BGP Communities control various functions of the route server.

If the <PEER ASN> value is a four byte AS number (4B ASN) you have to use BGP Large Communities (RFC 8092).

Control of Route Redistribution

You can control which BGP announcements you send to the route servers are redistributed to other peers. This can be done based on the following criteria:

  • ASN
  • switch

Redistribution can be controlled with BGP Communities and BGP Large Communities. Usage of BGP Large Communities is encouraged.

The table below gives an overview of available options and their corresponding BGP Communities. To get the value for <SWITCH> please refer to the rightmost field of the BGP Large Community overview table at Route Server Informational BGP Communities.

In case two or more BGP (Large) Communities are contradicting the community with the lowest evaluation order number wins.

Evaluation Order

Group

Action

BGP Community (RFC 1997)

BGP Large Community (RFC 8092)

1

Well-known

Well-known NO_EXPORT

65535:65281

/

Well-known NO_ADVERTISE

65535:65282

/

2

ASN based

Do not redistribute to <PEER ASN>

0:<PEER ASN>

For 4B <PEER ASN> use BGP Large Community1

{{RS_ASN}}:0:<PEER ASN>

3

Redistribute to <PEER ASN>2

{{RS_ASN}}:<PEER ASN>

65534:<PEER ASN> for RS with 4B ASN1

{{RS_ASN}}:1:<PEER ASN>

4

General

Do not redistribute to all

0:{{RS_ASN}}

0:65534 for RS with 4B ASN

{{RS_ASN}}:0:0

5

Redistribute to all (default)

{{RS_ASN}}:{{RS_ASN}}

65534:65534 for RS with 4B ASN

{{RS_ASN}}:1:0

1 Please contact Customer Service if your equipment does not support BGP Large Communities.

2Only useful in combination with one or more “do not announce” BGP communities with lower evaluation order (e.g. {{RS_ASN}}:1:<PEER ASN> can provide a selective override for {{RS_ASN}}:922:<METRO>).

The route servers remove the aforementioned BGP Communities and BGP Large Communities from a BGP announcement before redistributing it.

The well-known BGP Communities NO_EXPORT (65535:65281) and NO_ADVERTISE (65535:65282) are also honored meaning that a BGP announcement marked by one of these communities is not redistributed to any peer. If you want the route server to add a NO_EXPORT or NO_ADVERTISE community for a given BGP announcement before redistributing, you have to add the community ({{RS_ASN}}:65281) or ({{RS_ASN}}:65282) respectively. This is also possible on a per-peer basis using BGP Large Communities.

Action

BGP Community (RFC 1997)

BGP Large Community (RFC 8092)

add NO_EXPORT

{{RS_ASN}}:65281

65534:65281 for RS with 4B ASN

/

add NO_ADVERTISE

{{RS_ASN}}:65282

65534:65282 for RS with 4B ASN

/

add NO_EXPORT selective

/

{{RS_ASN}}:901:<PEER ASN>

add NO_ADVERTISE selective

/

{{RS_ASN}}:902:<PEER ASN>

More than one of the aforementioned BGP Communities and BGP Large Communities can be added to a single BGP announcement. {{IXP_SHORT}} recommends not to add more than 128 of these communities as it makes handling complex and error-prone. If you need to do this, please contact Customer Service.

All BGP Communities and BGP Large Communities that are not listed above are not touched by the route servers and transparently redistributed. For backwards compatibility, routes with no BGP Action Community at all are distributed to all peers as well. You can check this in the {{IXP_SHORT}} Looking Glass. If you type your ASN into the global search field, you will find all matching routes from all {{IXP_SHORT}} route servers on all {{IXP_SHORT}} Internet Exchanges. By clicking on a route, you get the route information dialogue with details (BGP Communities etc.). You can apply further filters, e.g. filter for a specific route server or IX.

For more details how to use the {{IXP_SHORT}} Looking Glass, see Looking Glass guide.

Usage Examples ({{IXP}})

BGP announcements marked with the following communities are only redistributed to AS64501 and AS64502 (both 2 byte ASNs):

  • 6695:0:0 (Do not redistribute to all)
  • 6695:1:64501 (Redistribute to 64501)
  • 6695:1:64502 (Redistribute to 64502)

BGP announcements marked with the following communities are redistributed to all peers/ASNs except AS64501 and AS64502:

  • 6695:0:64501 (Do not redistribute to 64501)
  • 6695:0:64502 (Do not redistribute to 64502)
  • 6695:1:0 (Do redistribute to all)

BGP announcements tagged with the following communities are only redistributed to AS65550 (4 byte ASN) and AS64501 (2 byte ASN):

  • 0:6695 (Do not redistribute to all)
  • 6695:1:65550 (Redistribute to 65550; BGP Large Community)
  • 6695:64501 (Redistribute to 64501)

Blackholing

If the route server receives a BGP announcement marked as a blackhole, the NO_EXPORT community (65535:65281) and the BLACKHOLE Community (65535:666) RFC 7999 are added if these communities are not already present. This makes sure each BGP announcement marked as a blackhole can be easily filtered and does not spread widely in the Internet routing system.

For more information, see Blackholing Guide.

AS Path Prepending

You can use BGP communities to prepend your own ASN up to three times. This can be done to all other peers or selective to only certain peers. If you add multiple of the following communities, only the highest prepend amount will be applied.

BGP Community (RFC 1997)

BGP Large Community (RFC 8092)

Prepend once

65001:0

{{RS_ASN}}:101:0

Prepend twice

65002:0

{{RS_ASN}}:102:0

Prepend three times

65003:0

{{RS_ASN}}:103:0

Prepend once selective

65001:<PEER ASN>

{{RS_ASN}}:101:<PEER ASN>

Prepend twice selective

65002:<PEER ASN>

{{RS_ASN}}:102:<PEER ASN>

Prepend three times selective

65003:<PEER ASN>

{{RS_ASN}}:103:<PEER ASN>

Graceful BGP Session Shutdown

The {{IXP_SHORT}} route servers support Graceful BGP Session Shutdown (RFC 8326). With this well-known BGP Community, you can instruct the route servers to calculate and redistribute an alternate path (if available) for your advertised routes before you commence your maintenance. This makes sure that routers of other customers have fully converged before you interrupt L2 connectivity and thereby so-called micro blackholing is prevented.

Details:

  • Setting BGP Community GRACEFUL_SHUTDOWN (65535:0) on all you advertised routes. The route server will set BGP local preference to 0 for these routes.
  • The route server will calculate alternative paths for your advertised routes (if available) and redistribute these to other peers. Routes with no alternative path will get redistributed with BGP Community GRACEFUL_SHUTDOWN.
  • You should also apply GRACEFUL_SHUTDOWN on the inbound policy of your eBGP session.
  • After BGP convergence, you can safely shut down the BGP session. At this point, routers of other customers have learned alternative paths for your routes (if available) from the route server and forward traffic on the new path.

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Penang IX Route Server Action BGP Communities

SEECIX GlobePEER Route Server Action BGP Communities

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