RE: Cisco Route filtering [was Re: OPS: BGP spew from ASN 7374]
I've had a question on this for some time that maybe can get answered here.
Let's assume for a moment that I have a network of 209.123/18 (1/4 of a classful B).
Let's further assume that my upstream filters me with:
access-list 2002 permit ip host 209.123.0.0 host 255.255.0.0 neigh 2.3.4.5 distrib 2002 in
Will my /18 announcement make it through this /16 filter?
No. The ACL specifies an exact match.
Would the same be true with a prefix-length filter, which I assume the syntax would be:
ip prefix-list 1 permit 209.123.0.0/16 neigh 2.3.4.5 prefix-list 1 in
Same deal. Chris
Let's assume for a moment that I have a network of 209.123/18 (1/4 of a classful B).
Let's further assume that my upstream filters me with:
access-list 2002 permit ip host 209.123.0.0 host 255.255.0.0 neigh 2.3.4.5 distrib 2002 in
Will my /18 announcement make it through this /16 filter?
No. The ACL specifies an exact match. You should change 'host 255.255.0.0' to '255.255.0.0 0.0.255.255' to allow any _more specific_ mask. Read CISCO docs.
Would the same be true with a prefix-length filter, which I assume the syntax would be:
ip prefix-list 1 permit 209.123.0.0/16 neigh 2.3.4.5 prefix-list 1 in
Same deal.
Chris
Aleksei Roudnev, Network Operations Center, Relcom, Moscow (+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 230-41-41, N 13729 (pager) (+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)
participants (2)
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Alex P. Rudnev -
Martin, Christian