route-map bug in IOS XE?

[hocus-pokus-alakazoo]

I'm using Cisco IOS XE Software, Version 16.06.08

I have eBGP setup with a customer.  The eBGP peering uses inbound/outbound route maps to filter advertised/received prefixes.   I'm advertising 40k+ prefixes to the eBGP peer. The bizarre thing is that my outbound route map invokes a non-existent prefix list.  Shouldn't I advertise nothing to the eBGP peer as a result?

router bgp abc
bgp router-id 1.2.3.4
bgp log-neighbor-changes
neighbor 1 remote-as xyz
neighbor 1 description Peer to acme
neighbor 1 route-map RM_FROM_acme in
neighbor 1 route-map RM_TO_acme out

route-map RM_TO_acme permit 10 
match ip address prefix-list PL_mycompany_TO_acme

prefix-list PL_mycompany_TO_acme does not exist in config.....so why am I advertising every prefix to neighbor 1?  shouldn't default behavior be to advertise no prefixes to neighbor 1?

[balaji.bandi]

what deive ? try to upgrade to 17.9.4a or higher and test it.

also can you provide configuration bits here.

[MHM Cisco World]

If the route-map is permit without match anything the action will be advertise prefix 

If the route-map is deny without match anything then action will not advertise any prefix.

MHM

[hocus-pokus-alakazoo]

the outbound route map invokes a prefix list that doesn't exist...so how is that there is no outbound filtering in place? I would think that nothing would be advertised as a results of this scenario.

[MHM Cisco World]

Can I see route-map?

MHM

[Harold Ritter · Accepted solution]

Hi @hocus-pokus-alakazoo ,

A non existent prefix list causes the match statement to match all prefixes. 

Regards,

[hocus-pokus-alakazoo]

is that true across all versions of IOS?  

[Harold Ritter]

Hi @hocus-pokus-alakazoo ,

This has been the behavior for as long as I can remember.

Regards,

[hocus-pokus-alakazoo]

please see config example in original post

[MHM Cisco World]

 

The prefix list have deny any in end 

The route map is permit 

So prefix is deny and route map is permit the action is NO action.

It not bug it normal behavior of route map in ios and ios xe.

Ios xr use rpl not route map.

MHM

[Harold Ritter]

Hi @MHM Cisco World ,

The OP says that the prefix list is non existent. So the behavior is the one I mentioned above.

Regards,

[Ruben Cocheno]

@hocus-pokus-alakazoo 

The IOS/IOSXE doesn't validate if the prefix-list exists or not, so any typo on assigning it will cause that behaviour, which is bypass. instead of blocking.

[David Ruess]

In addition to what @Harold Ritter said its like when people add a second route-map statement (usually entry 20 as the first entry is 10) with just a permit statement permitting all routes. It doesn't have a match in it either. See below:

route-map RM_to_acme permit 10

match ip address prefix-list PL_mycompany_TO_acme

set tag 55

route-map RM_to_acme permit 20

The above config would set a tag of 55 to any route matching the defined prefix list. The second Route-map statement permits all other routes. Because I want to allow ALL routes but only want to tag a select few. Your 1 line route-map is essentially doing what the second statement in mine is doing.

I didn't see it mentioned but you could just change the  route-map RM_to_acme permit 10 to a route-map RM_to_acme deny 10 with no PL specified and it wont advertise anything to the BGP peer.

-David

[MHM Cisco World]

I try find command help you in detect the route-map permit or deny prefix 
command can help you is 
show ip bgp route-map

this give you the prefix permit by this prefix 

MHM