Redistribution Behavior When Prefix-List Is Missing in Route-Map

[Haruki Horiguchi]

Hello,
I am using a Catalyst 9500-24Y4C switch running IOS XE Software version 16.12.04. I have configured the device to redistribute BGP-learned routes into EIGRP using a route-map with the following metrics: metric 1000000 10 255 1 1500.
Here is the route-map configuration:

route-map eigrp1 permit 10
 match ip address prefix-lists group1 group2
route-map eigrp1 permit 20
 match ip address prefix-lists group3
 set metric 1000000 20 255 1 1500


Prefix list group1 has been removed and does not exist.
Question is:How does Catalyst behave when group1 is missing?
Will it treat group1 as "any" and match all BGP-learned routes with Sequence 10, redistributing them with the metric 1000000 10 255 1 1500?

I appreciate your insights.

[M02@rt37]

Hello @Haruki Horiguchi 

The absence of group1 does not cause the route-map to implicitly match all routes as if it were treated as “any.” It simply means that sequence 10 will be skipped because it has no matching criteria.

 Only routes that match existing prefix lists will be redistributed according to the specified route-map actions. In your case, without group1, only routes matching group3 will be redistributed, if any.

[paul driver]

Hello
As it still being called in the route-map, even if the the prefix-list is non existent it will allow everything as it a catch all,
so even if your other prefix group is specifying certain routes the non existent prefix will catch everything else and redistribute it.

[M02@rt37]

@Haruki Horiguchi @paul driver 

When a route-map contains a match statement for a prefix list that does not exist, that match condition effectively fails. This means that no routes will match this specific entry in the route-map.

In this case, with the first sequence referencing group1, because that prefix list has been removed, no routes will match this sequence.

The route-map will continue to evaluate the next sequence(s) after the first one. In the example, 'sequence 20' will check for matches against group3. If any routes match the prefixes defined in group3, those routes will be redistributed with the specified metric.

The route-map does not treat a non-existent match condition as a catch-all. It does not redistribute everything if the previous match fails. Instead, only those routes that match the subsequent entries will be redistributed. If there are no matches in either sequence 10 or sequence 20, then no routes will be redistributed at all.

[MHM Cisco World]

any missing prefix use for route-map make route-map match ANY

MHM

[paul driver · Accepted solution]

Hello M02@rt37 

When a route-map contains a match statement for a prefix list that does not exist, that match condition effectively fails. This means that no routes will match this specific entry in the route-map.

In this case, with the first sequence referencing group1, because that prefix list has been removed, no routes will match this sequence

---

Unfortunately your incorrect - Having a non existent prefix in the route-map will match ALL so in this instance
the GROUP1 prefix will allow any other prefixes that the GROUP2 prefix is not calling

[MHM Cisco World]

Totally correct 

MHM

[M02@rt37]

I've just verified. And you're right @paul driver ! Thanks for that clarification.

[Haruki Horiguchi]

Thank you for your help.
Judging from other people's opinions, your opinion seems to be correct.