Route-map

[Roel Reyes]

Hi, 

i have this config and output: 

router bgp 1111
bgp log-neighbor-changes
neighbor 172.30.0.10 remote-as 700
neighbor 172.30.0.10 soft-reconfiguration inbound
neighbor 172.30.0.10 route-map local-pref in
neighbor 172.30.0.10 filter-list 1 out
neighbor 192.168.1.5 remote-as 1111
neighbor 192.168.1.5 next-hop-self
!
ip forward-protocol nd
!
ip as-path access-list 1 permit ^$
ip as-path access-list 2 permit .*
!
ip prefix-list 20.20.20.0/24-route seq 5 permit 20.20.20.0/24
!
route-map local-pref permit 10
match ip address prefix-list 20.20.20.0/24-route
set local-preference 150
!
route-map local-pref permit 20
!

But if i removed this line: route-map local-pref permit 20 

2.2.2.0/24 is gone

router bgp 1111
bgp log-neighbor-changes
neighbor 172.30.0.10 remote-as 700
neighbor 172.30.0.10 soft-reconfiguration inbound
neighbor 172.30.0.10 route-map local-pref in
neighbor 172.30.0.10 filter-list 1 out
neighbor 192.168.1.5 remote-as 1111
neighbor 192.168.1.5 next-hop-self
!
ip forward-protocol nd
!
ip as-path access-list 1 permit ^$
ip as-path access-list 2 permit .*
!
ip prefix-list 20.20.20.0/24-route seq 5 permit 20.20.20.0/24
!
ip prefix-list prepend-0.0.0.0/0 seq 5 permit 0.0.0.0/0 le 32
!
ip prefix-list prepend-20.20.20.0/24 seq 5 permit 20.20.20.0/24
!
route-map local-pref permit 10
match ip address prefix-list 20.20.20.0/24-route
set local-preference 150
!

as far as i know, 2.2.2.0/24 should be gone with the first statement as it will be denied due to implicit deny. i dont know why it is still accepted and received.

[Georg Pauwen]

Hello,

that is expected behavior:

route-map local-pref permit 10
match ip address prefix-list 20.20.20.0/24-route
set local-preference 150

--> the first part sets the local preference for the specified prefix list to 150

route-map local-pref permit 20

--> the second part allows everything else that doesn't match the prefix list, with the default values

[Roel Reyes]

Hi,

but the ip prefix list has implicit deny? so when non - 20.20.20.0/24 route comes in it will be denied? a denied route or packet will proceed to seq 20?

ip prefix-list 20.20.20.0/24-route seq 5 permit 20.20.20.0/24

[Georg Pauwen]

Hello,

the implicit deny is only for setting the local preference. With your second line (route-map local-pref permit 20) you allow everything else, with the default values...

[Roel Reyes]

Hi,

I thought implicit deny on route map will let packet untouched, then why removing the seq 20 will let 2.2.2.0/24 get filtered? 2.2.2.0/24 should remain to default local pref since it will not matched the route map on the first seq

[Georg Pauwen]

Hello Roel,

the implicit deny filters all routes not specified, if you want to allow everything else with the default values, you need the second line. That is just how a route map works...

[Roel Reyes]

Hi,


thanks for the clarification, do you have any good resource about
route-map? tried to search cisco route map but cannot find very specific
definitions.

[Georg Pauwen · Accepted solution]

Hello,

have a look at the two links below which I think explain the concept well. In your case, the important part is:

" If a route-map entry does not explicitly specify any matching conditions, then it always matches."

http://docs.frrouting.org/en/latest/routemap.html

https://www.examcollection.com/certification-training/ccnp-concept-of-route-maps.html

[fbabashahi]

Hi ,first of all you use first line just for setting local preference not anything else and second line is empty that means everything else allowed , second i think this is because you use permit in your route-map if i remember right in logical process when you use deny in route-map command the match parameters will completely denied . look at the logic process of route map in image