something strange about bgp community

Song Li refresh.lsong at
Wed Jan 7 13:35:35 UTC 2015

Hi everyone,

Today when I check one route in Routeviews I find something strange as 

route-views>sh ip bgp
BGP routing table entry for, version 23405621
Paths: (33 available, best #28, table default)
   Not advertised to any peer
   Refresh Epoch 1
   202018 35320 35320 57800 from (
       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?


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 at

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