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Webcast-Catalyst9k
New Member

understanding route maps

I'm trying to understand the complexities of Policy Based Routing.

Cisco's web site http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800c75d1.html#1000872

states:

Route maps are composed of statements. The route map statements can be marked as permit or deny, and they are interpreted in the following ways:

If the packets do not match any route map statements, then all the set clauses are applied.

(The above is the one I'm having trouble with since it seems to conflict with the last one below.)

If a statement is marked as deny, the packets meeting the match criteria are sent back through the normal forwarding channels and destination-based routing is performed.

If the statement is marked as permit and the packets do not match any route map statements, the packets are sent back through the normal forwarding channels and destination-based routing is performed.

Can someone comment on this or point me to a link that is a little less confusing?

Thanks - Phil

3 REPLIES

Re: understanding route maps

For Policy routing, If route maps are written with permit:

packets matching a match statement are policy routed, packets don't match a statement are not policy routed, if a route-map block contains only set statements, these sets are applied. And there's an implicit deny at the end of the route-maps like ACLs. If statements are written with deny, packets matching are routed normally.

Regards

New Member

Re: understanding route maps

I understand the permit and deny part. What is confusing is the first part that states that if nothing matches then all the set clauses are applied?? That seems to contradict the reason for a route-map to begin with.

Re: understanding route maps

If a route-map used for policy routing consists of a permit entry whinch includes no match statements and some set statements, it's accepted match and set clauses are applied. I think this is what is meant. It can be thought as a way of overriding implicit deny of route-maps.

Regards.

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