08-29-2013 06:17 PM - edited 03-04-2019 08:54 PM
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.
------------------------------------------------------------------------------
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.
08-30-2013 12:40 AM
Hi,
These are the only well-known communities and others are just custom-made.
Regards
Alain
Don't forget to rate helpful posts.
08-30-2013 05:44 AM
Hi Sarah,
The complete list of BGP well know communities available is at the following URL.
Regards
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: