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BGP community anf rfc 1997

Unanswered Question
Aug 29th, 2013
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  • Bronze, 100 points or more

Hi everybody.


When i look at list a BGP router cheks to choose the best bgp route, I don't see " community" is listed. My understanding is we can use community to identify the group of routes and manipulate their attributes such as setting prepending AS, MED value etc thereby controlling which BGP route will be chosen as the best.



I find this rfc 1997 which describes three communities:


NO-EXPORT

NO- Advertise

NO -Export-Subconfed


Let say we have a BGP router(R1) which receives a prefix 2.0.0.0 with " NO-Export"  community from neighbor R2 . R1 is also receiving the same prefix from R3 but without any community.


This is my understanding:


our router as usual go down the list to choose the best routes. Let say R1 chose prefix from R2. R1 installs it into its routing table but it would not advertises it to any egp peer.


So the above mentioned community has no bearing on route selection process. They just tell router whether to advertises it to ebgp or not( as is the case with No-ExPORT community.


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Do we have more standardized communities in addition to what rfc 1997 describes, that every bgp router when receives it, understand what to do with the prefix? ( for example in rfc 1997, we have three communities as mentioned above, which are standardized)





thanks and have a great day.

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Overall Rating: 5 (2 ratings)
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cadet alain Fri, 08/30/2013 - 00:40
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  • Purple, 4500 points or more

Hi,

These are the only well-known communities and others are just custom-made.


Regards


Alain



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