route-map logic

[Gucamole]

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'

[Deepak Kumar]

Hi, 

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

[Martin L]

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
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[Giuseppe Larosa]

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