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Gucamole
Beginner

route-map logic

I just started learning about route-maps & prefix-list. It was confusing but I did a small lab in gns3 which has helped me to gain more clarity. I have created a simple mind-map to reference until I cement down the logic.

I wanted to ask if you could review to make sure I am understanding this correctly. I applied this in an eigrp instance with distribute-list 'in'route-map logic.png

3 REPLIES 3
Deepak Kumar
VIP Advocate

Hi, 

Thanks, it's good mind map and seems correct. 

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution if this comment will help you!
Martin L
VIP Advocate

 

How or where or what purpose were those Route-maps use for? 

it seems that route-maps can have opposite results when apply to redistribution of protocols comparing to other usage of Rout-Maps. 

 

 

Regards, ML
**Please Rate All Helpful Responses **

Giuseppe Larosa
Hall of Fame Master

Hello @Gucamole ,

your understanding is correct.

when using route-maps for filtering redistributions or distribute-list the key command is in the route-map clause

A route-map clause (block) with a permit action will allow prefixes that are a match for the underlying ACL or prefix-lists and those prefixes permitted will be allowed / sent / redistributed with no further processing of other route-map blocks.

IF the route-map action is permit and the prefix is not permitted on the prefix-list or ACL it will be processed by following blocks if any. If no other route-map blocks exist the prefix will be denied by implicit deny any in the route-map logic.

If the route-map action is deny and the prefix is allowed (= permit in the ACL or prefix-list ) the prefix will be denied = filtered with no further processing.

I f the route-map action is deny and the prefix is not allowed (=deny in ACL or prefix-list or implicit deny at the end) the prefix will be processed by following route-map blocks using the same logic explained above.

 

To be noted when using a route-map for PBR the implicit deny any becomes use standard destination based routing for all prefixes hitting this point.

So as noted in different contexts a prefix denied by a route-map can be simply routed by destination.

 

Hope to help

Giuseppe