Route maps

Unanswered Question
Sep 24th, 2009
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All,


I'm a little confused about route map functionality with regards to the deny statement. Do the following all do the same thing?


Ex. 1:

access-list 5 deny 1.1.1.0 0.0.0.255

access-list 5 permit any


route-map TEST permit 5

match ip address 5

route-map TEST permit 10


Ex. 2:

access-list 5 permit 1.1.1.0 0.0.0.255


route-map TEST deny 5

match ip address 5


route-map TEST permit 10



For some reason, I get caught on the deny clause. When it denies, does it actually deny those routes from being processed at all? If I were to apply the first example to a neighbor for bgp, would the 1.1.1.0 not show up in the routing table? It seems like it doesn't, but I want to make sure that I'm looking at this right.


*Edit: Actually, the route map doesn't stop the route from being put into the table. Are the deny statements ONLY for processing weights, metrics, etc, and if I need to deny a route from getting into the table, I should use a distribution list?




Thanks,

John


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Giuseppe Larosa Thu, 09/24/2009 - 11:30
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Hello John,


when you use a route map deny statement if a prefix is permitted by the ACL it is actually filtered.


but if you have a route map deny statement with an ACL that denies a prefix that prefix is not filtered but left in basket and so can be permitted by the second clause.


So the two route-maps do different things:


first route-map allows only prefix 1.1.1.0/24 as a result of denying it and the permit any that will cause all other prefixes to be denied.


second route-map denies 1.1.1.0/24 and allows all other prefixes with second clause.


Hope to help

Giuseppe


John Blakley Thu, 09/24/2009 - 11:32
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Giuseppe,


Would you say that the second example would act like a distribution list filter?


Thanks,

John

Giuseppe Larosa Thu, 09/24/2009 - 12:27
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Hello John,

second route-map is equivalent to apply the acl 5 of first example as a distribute-list.



This looks like strange, isn't it?


Hope to help

Giuseppe


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