BGP attributes V/S BGP Comunity

[Arjun Dabol]

Have a small doubt : what is the difference between BGP attributes AND BGP Communities ?

[Richard Burts · Accepted solution]

BGP attributes are aspects of the route which are sent in the advertisement such as AS path, and route source. BGP community is a value that you can assign for a prefix as it is being advertised. As such you can say that BGP community is a particular type of BGP attribute.

HTH

Rick

[Richard Burts]

I am glad that my answer was helpful. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify discussions that have helpful information.

HTH

Rick

[Arjun Dabol]

Thanks Rick. can you help me understand how to use "own community values" ?

I know there are two type of bgp communities : "predefined / well-known community values" as well as we can also define our own community values - so my question is how to use / define and implement the own community values ?

[Richard Burts]

The community value is advertised to BGP peers to communicate additional information about a prefix and usually to cause some different behavior from the peer about the prefix. So the first step in using your own community is to determine what information you want to communicate about a prefix and what different behavior you want. You then choose a value that you will use for the community.

The next step is to negotiate with your BGP peer to get them to agree to accept and process the specified community and to implement the different behavior.

Then you make the configuration changes in your BGP to send that community value.

HTH

Rick

[Arjun Dabol]

One more Q : -

from configuration point of view : is it always has to be thru route-map ?

[Richard Burts · Accepted solution]

I am not sure that I fully understand your question. But if you want to set values in the BGP community or if you want to control behaviors based on the community then yes using route maps is the way to achieve these goals.

HTH

Rick

[Joseph W. Doherty]

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Posting

It's really up to the two parties, sharing community values, to determine how they wish to use them and what a particular community value means.  Some what commonly, the top half of a community value represents the AS the community is for and the bottom half of the community is a weight to apply to route.  (I.e. communities are often used to manipulate how traffic will be routed.)

I also want to mention, more than one community might be attached to a route prefix.