Re: something strange about bgp community

[joel jaeggli <joelja () bogus com>]

2914:429 is ntt's do not advertise to any peer community

bgp communities are transitive attributes, e.g. you can just pass them
to peers unmolested.  so someone that's presumably not ntt ( e.g. the
neighbor is digital ocean) is sending that commmunity to route views as
part of their export.

Their utility in routviews depends on context, when I see communities I
tagged on my own routes in routviews for example I can tell what pop the
announcement  originated from which is rather useful. other's like the
one above do tell you something about the policy of somebody on the
internet. you can also tell who strips communities...

On 1/7/15 5:35 AM, Song Li wrote:
> Hi everyone,
>
> Today when I check one route in Routeviews I find something strange as
> follows:
>
> route-views>sh ip bgp 176.108.0.0
> BGP routing table entry for 176.108.0.0/19, version 23405621
> Paths: (33 available, best #28, table default)
>   Not advertised to any peer
>   Refresh Epoch 1
>   202018 35320 35320 57800
>     5.101.110.2 from 5.101.110.2 (5.101.110.2)
>       Origin IGP, localpref 100, valid, external
>       Community: 702:120 2914:429 20485:52990 20485:53990 20485:54040
> 20485:54050 47541:10001
>       rx pathid: 0, tx pathid: 0
>
> the AS-Path is "202018 35320 35320 57800" but the community is 702:120
> 2914:429 20485:52990 ....
>
> According to RFC 1997, the community format is AA:NN and AA means the
> AS#. Here, AS702, AS2914 and AS20485 do not appear in the AS-Path and
> as a result they should not appear in the community. Could anybody
> tell me what's the reason they do appear in the community of this route?
>
> Thanks!

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