From: Jonathan Hays (nomad@gfoyle.org)
Date: Sat Mar 06 2004 - 09:38:09 GMT-3
you wrote:
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
>Behalf Of Ahmed Mustafa
>Sent: Saturday, March 06, 2004 4:10 AM
>To: ccielab@groupstudy.com
>Subject: Empty Route-maps
>
>
>What is the best way to remember the rules of Empty Route-map
>Statements. For
>example,
>
>
>Route-map PREPEND permit 10
>match ip address prefix-list ALLOWED
>set as-path prepend 200 200
>
>Route-map PREPEND permit 20 (This is an empty route statement)
>
>
>I see that sometimes it is necessary to configure empty
>route-statement, and
>sometimes it is not. I know it is tied to "IMPLICIT DENY" for
>the access-list
>rules, but mosty affects with the Interface command "IP ACCESS-GROUP".
>
>How does it affect the route-map statements.
>
>Regards,
>
>Ahmed
= = =
The empty route-map has just the opposite effect - it implicity MATCHES
everything not matched by the first route-map statement. An empty
route-map statement is the equivalent of this:
access-list 1 permit any
!
route-map PREPREND permit 20
match ip address 1
So the overall effect of the route-map is to prepend routes that match
the ALLOWED access list and allow everything else through without
prepending (done by the empty route-map line). With BGP, if you don't
have the second empty route-map statement, anything that does not match
ALLOWED is dropped.
HTH,
Jonathan
This archive was generated by hypermail 2.1.4 : Thu Apr 01 2004 - 08:15:15 GMT-3