Using the as-set keyword creates an aggregate entry using the same
rules that the command follows without this keyword, but the path
advertised for this route will be an AS_SET consisting of all elements
contained in all paths that are being summarized. Do not use this form
of the aggregate-address command when aggregating many paths, because
this route must be continually withdrawn and updated as autonomous
system path reachability information for the summarized routes changes.
http://www.cisco.com/en/US/docs/ios/12_3/iproute/command/reference/ip2_a1g.html#wp1037074
I hope this helps.
I can't see why you would want to use it anyways unless you have a
transit AS and I would question the use there as well. I know I
wouldn't want one of my isp's to aggregate my prefixes. Maybe if you
have a single ISP and you ip space was assigned by that ISP but then I
would question the need to have an AS and the need to run BGP.
Am I missing something?
Sent from my iPhone
On Jan 19, 2010, at 12:21 PM, Brad Edgeworth
<[email protected]> wrote:
I just re-read TCP/IP Vol 2 this weekend (I know Mr. Excitement) and
after reading through some of his examples on aggregation. One of
my major questions is why wouldn’t we use the AS-SET when we’re
only doing Summary-Only. (More specifically in the real world)
IE.
Router BGP 100
Aggregrate-address 128.83.0.0 255.255.0.0 summary-only as-set
I also found that the FILTER-LIST command is a lot easier than do
neighbor route-maps when filtering off of just AS-Paths. Is there
a rule of logic when you have a ROUTE-MAP and FILTER-LIST. Does
it apply against both?
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