From: Brian Edwards (bedwards@xxxxxxxxxxx)
Date: Fri May 26 2000 - 19:58:08 GMT-3
The access-list is interpreted differently when you apply it to a route map
that is filtering BGP updates. It is interpreted as follows
[prefix] [wild-card mask for prefix] [subnet mask] [wild-card
mask for subnet mask]
for example 160.0.0.0/8 only would be
access-list 101 permit ip 160.0.0.0 0.0.0.0 255.0.0.0 0.0.0.0
and 160.8.0.0/16, 160.9.0.0/16, 160.10.0.0/16, and 160.11.0.0/16 only would
be
access-list 101 permit ip 160.8.0.0 0.3.0.0 255.255.0.0 0.0.0.0
-----Original Message-----
From: Earl Aboytes [mailto:earl@linkline.com]
Sent: Friday, May 26, 2000 3:10 PM
To: ccielab@groupstudy.com
Subject: Prefix filtering (BGP)
Here is a kewl question.
Can anyone explain what is going on here?
Using access lists to filter supernets is a bit tricky. Assume, for
example, that a router has different subnets of 160.10.x.x and you want to
advertise 160.0.0.0/8 only. The following access list would permit
160.0.0.0/8, 160.0.0.0/9 and so on (remember, this is a class B address
space). access-list 1 permit 160.0.0.0 0.0.0.255
To restrict the update to 160.0.0.0/8 only, you have to use an extended
access list, such as the following:
access-list 101 permit ip 160.0.0.0 0.255.255.255 255.0.0.0 0.255.255.255
What are they talking about!?!?!?!?
To me it looks like the destination network is 255.0.0.0/8. Is that what is
supposed to be going on here? Can anyone shed some light on this?
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