Thanks! Because there is no standard syntax on the description of BGP community, I think the problem is hard to understand. 在 2015/1/7 23:25, joel jaeggli 写道:
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!
-- Song Li Room 4-204, FIT Building, Network Security, Department of Electronic Engineering, Tsinghua University, Beijing 100084, China Tel:( +86) 010-62446440 E-mail: refresh.lsong@gmail.com