Re: AS SET

Someone already mentioned the answer to your question, which is for
loop prevention. AS path information is lost when you aggregate this
way. Actually the preferred way to aggregate with BGP is to create a
static route for the shorter prefix and distribute (network command)
or redistribute into BGP. Route filters should be configured toward
peers so that only the less specific prefixes are advertised.

Why?

It prevents the constant changing of the as-set when a component of
the aggregate changes. In fact, the point of aggregation is to hide
topology information or state changes, so you wouldn't want the less
specific prefix to change as a result of one of the components
changing. This also simplifies configuration as the aggregate is
treated as any other route from a configuration perspective.

Ronnie

On Sun, Mar 14, 2010 at 3:12 PM, Muzammil Malick <malickmuz_at_gmail.com> wrote:
> Hi
>
> Could someone please help me out and explain why you would include AS
> information in a bgp summary (aggregate-address 10.0.0.0 255.255.0.0
> summary-only as-set)
>
> I know what it does and how to use it but why from a design perspective
> would you want to send AS information as apart of a summary.
> Can someone provide an example?
>
>
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-- 
Ronald Angello
Network Architect
CCIE 17846
CCDP, CCIP, CCNP
Blogs and organic groups at http://www.ccie.net