Route Maps and Redistribution

Multiple match criteria in the same line of a route map are processed with OR logic. Separate match criteria can also be applied vertically under a route map line that uses AND logic. In this case, route-map sequence 10 has multiple match statements listed vertically. Therefore, seq 10 uses AND logic and the packet must match both ACL1 and ACL2. The question states that the packet only matches ACL1. As a result, there is no match and sequence 20 is checked. Sequence 20 has a single match clause with multiple criteria. Therefore, it uses OR logic and the packet can match ACL1 or ACL2. According to the question, it matches ACL1; therefore, the packet is denied based on route-map sequence number 20.
For the packet to be permitted by sequence number 10, it must match all the criteria within the statement. In this case, it only matches ACL1.
Since the packet meets the criteria for sequence number 20, it will be denied by the statement and not the implicit deny any at the end of the route map.
Like access lists, route maps contain an implicit deny any as their last statement. Any packet not matching previous statements will be denied by the route map.

https://www.ciscopress.com/articles/route-maps

Question: Refer to the following partial route map:

route-map MyRouteMap permit 10
match ip address ACL1
match ip address ACL2
route-map MyRouteMap deny 20
match ip address ACL1 ACL2

Which action will be taken if a packet only matches ACL1?

A. The packet will be permitted by sequence number 10.

B. The packet will be denied by sequence number 20.

C. No action will be taken.

D. The packet will be denied by the implicit deny any at the end of the route map.

Correct answer: B

It is very likely that routing loops are introduced when you use multipoint two-way redistribution. Two solutions are to redistribute only internal routes, and to use route tagging.

To avoid routing loops, either use route maps to only redistribute internal routes or use route tagging.
To avoid routing loops, either use route maps to redistribute only internal routes or use route tagging. A route tag is a 32-bit value that is attached to the redistributed routes.

Redistributing only external routes is not a way to prevent routing loops. To avoid routing loops, either use route maps to redistribute only internal routes or use route tagging. You are not able to redistribute external routes without potentially creating loops.

Redistributing internal and external routes is not a way to prevent route loops. To avoid routing loops, either use route maps to only redistribute internal routes or use route tagging. You are not able to redistribute external routes without potentially creating loops.