I am trying to understand the BGP ATOMIC AGGREGATE attribute from a BGP router which receives aggregate routes. Can somebody tell me what is the action taken by a BGP router when it receives a aggregate route with ATOMIC AGGREGATE.

I understand that the ATOMIC AGGREGATE is used when there is loss of information while aggregating the routes. But what does the receiver of the attribute do with the information. what kind of action does it take ?

It serves as an indication to the receiver that it can't "deaggregate" the prefix per some of the granularity associated with the NLRI of that route (i.e. AS paths) may have been lost when the aggregate was created, and deaggregation could result in the introduction of loops.

If anyone can put some light on how this BGP attribute gets utilized in the real world i would greatly appreciate.

However, I don't believe many folks actually deaggregate routes in real networks (at least not intentionally :-). I've seen several implementations which don't correctly attach the attribute, though it didn't break anything at the time. In the future, queuries of this nature may be more appropriately directed to the IDR WG list (bgp@ans.net). -danny