[AusNOG] OPTUS BGP Communities

[Chris Chaundy]

You can tag a single announcement with many community values (not sure
what the real limit is if there is one).  Carriers usually have ones
that customers can set, and others that cannot be set (and they use for
their own devious purposes).  Other than the setting local preference
(which customers can set), other common usages are geographical origin,
customer / internal / peer / transit routes, type of connection service,
etc. (which they cannot set).  You can even potentially pass communities
transitively through to your provider's provider(s).

0x00000000 thru to 0x0000FFFF and 0xFFFF0000 thru to 0xFFFFFFFF are
reserved and there are 3 well known communities: NO_EXPORT (0xFFFFFF01),
NO_ADVERTISE (0xFFFFFF02) and NO_EXPORT_SUBCONFED (0xFFFFFF03).
Generally the first 16 bits are the AS number to whom the community
value is significant and the remaining 16 bits is the community value
for that specific AS.  See RFC 1997 for more details.  I need to do some
reading to see how this works now that we are getting 32 bit AS numbers
(extended communities maybe?).

Cheers, Chris

-----Original Message-----
From: ausnog-bounces at ausnog.net [mailto:ausnog-bounces at ausnog.net] On
Behalf Of Sean K. Finn
Sent: Friday, 20 June 2008 4:21 PM
To: 'Gavin Tweedie'
Cc: Oz Servers NOC; 'ausnog at ausnog.net'
Subject: Re: [AusNOG] OPTUS BGP Communities

Cheers,

Appears current, not sure if they use extra communities though.

The communities listed look like they are to determine preference in
case of a routing tie over which path to take to get into the Optus
customers network, but so far I haven't seen any community ID's that are
listed that will prevent / limit the depth of where our BGP announcement
goes to geographically/continentally.


They do appear to have state-based community tags, but is it possible to
tag a single announcement with multiple BGP community ID's?


I have a request in with the Optus guys for more specific info, haven't
heard back yet one way or another though.

Cheers,
Sean.


> Not sure how current this info is:
> http://looking-glass.optus.net.au/notes.html

> Gav
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