🔍 BGP Route Map Troubleshooting Lab

ip prefix-list CUSTOMER-A seq 10 permit 172.16.10.0/25
!                                                    ^^^
!  /25 does not match the /24 network being advertised

no ip prefix-list CUSTOMER-A seq 10
ip prefix-list CUSTOMER-A seq 10 permit 172.16.10.0/24

! Soft reset to re-advertise with correct community
R1# clear ip bgp 192.168.12.2 soft out

Root cause: The prefix-list used /25 instead of /24, so 172.16.10.0/24 never matched. The route-map permitted clause was never evaluated, and the community 100:10 was never set. The route still went out via the implicit seq 20 permit, just without any community.

neighbor 192.168.23.3 route-map SET-LOCPREF out
!                                            ^^^
! Applied outbound — but local-pref is set on RECEIVED routes (inbound)

R2(config)# router bgp 200
R2(config-router)# address-family ipv4
R2(config-router-af)#  no neighbor 192.168.23.3 route-map SET-LOCPREF out
R2(config-router-af)#  neighbor 192.168.23.3 route-map SET-LOCPREF in
R2(config-router-af)#  end
R2# clear ip bgp 192.168.23.3 soft in

Root cause: local-preference is set on routes received from a peer — it is an inbound attribute from the perspective of the router processing it. Applying the route-map outbound means it runs against routes being sent to R3, where setting local-pref has no effect (local-pref is not propagated over eBGP).

! R2 address-family ipv4:
neighbor 192.168.23.3 activate
! ← send-community missing
neighbor 192.168.24.4 activate
! ← send-community missing

R2(config)# router bgp 200
R2(config-router)# address-family ipv4
R2(config-router-af)#  neighbor 192.168.23.3 send-community
R2(config-router-af)#  neighbor 192.168.24.4 send-community
R2(config-router-af)#  end
R2# clear ip bgp 192.168.23.3 soft out
R2# clear ip bgp 192.168.24.4 soft out

Root cause: By default, IOS/IOS-XE does not advertise communities to eBGP peers. The send-community command must be explicitly configured per neighbour. Without it, all community values are stripped before the UPDATE is sent — there is no error or log message.

route-map PREPEND-R4 permit 10
 match ip address prefix-list PREPEND-PREFIX
 set as-path prepend 200 200
! ← no seq 20 permit — implicit deny blocks everything else

R2(config)# route-map PREPEND-R4 permit 20
R2(config-route-map)#  exit
R2# clear ip bgp 192.168.24.4 soft out

Root cause: Route-maps, like ACLs, have an implicit deny all at the end. When a route-map is used for BGP advertisement filtering, any route not matched by an explicit permit sequence is blocked. Adding an empty permit sequence at a higher sequence number passes all unmatched routes unchanged.

ip community-list expanded BAD-COMM-MATCH permit 200:50
!              ^^^^^^^^
!  'expanded' treats the value as a regex pattern, not a literal community
!  '200:50' as a regex matches substrings — unintended and unreliable

R3(config)# no ip community-list expanded BAD-COMM-MATCH
R3(config)# ip community-list standard GOOD-COMM-MATCH permit 200:50
!
R3(config)# route-map MATCH-COMMUNITY permit 10
R3(config-route-map)#  match community GOOD-COMM-MATCH
R3(config-route-map)#  set local-preference 150
R3(config-route-map)#  exit
R3# clear ip bgp 192.168.23.2 soft in

Root cause: ip community-list standard matches exact community values. ip community-list expanded matches using POSIX extended regular expressions against the community string. Using expanded with a plain community value like 200:50 treats the colon as a regex literal and may produce unreliable results across IOS versions. Always use standard for exact community matches.

! address-family ipv4 on R4:
neighbor 192.168.24.2 activate
! ← soft-reconfiguration inbound missing

R4(config)# router bgp 400
R4(config-router)# address-family ipv4
R4(config-router-af)#  neighbor 192.168.24.2 soft-reconfiguration inbound
R4(config-router-af)#  end

! Trigger a soft reset to populate the Adj-RIB-In
R4# clear ip bgp 192.168.24.2 soft in

! Now this should return data
R4# show bgp ipv4 unicast neighbors 192.168.24.2 received-routes

Root cause: Without soft-reconfiguration inbound, IOS does not store a separate copy of the pre-policy received routes. This makes it impossible to compare what a peer sent versus what survived inbound policy — a critical troubleshooting capability. On IOS-XE with route-refresh capability negotiated, a soft reset can dynamically re-request routes, but storing the Adj-RIB-In with soft-reconfiguration inbound is best practice in lab environments.

router bgp 400
 neighbor 192.168.24.2 remote-as 200
 neighbor 192.168.24.2 route-map SET-WEIGHT in
 !                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 !  Applied at global level — ignored for IPv4 unicast address-family
 !
 address-family ipv4
  neighbor 192.168.24.2 activate
 exit-address-family

R4(config)# router bgp 400
R4(config-router)# no neighbor 192.168.24.2 route-map SET-WEIGHT in
R4(config-router)# address-family ipv4
R4(config-router-af)#  neighbor 192.168.24.2 route-map SET-WEIGHT in
R4(config-router-af)#  end
R4# clear ip bgp 192.168.24.2 soft in

Root cause: In modern IOS/IOS-XE with address-family support, neighbor route-map must be configured inside the address-family where it applies. A neighbor route-map statement at the global BGP level may be accepted by the parser but is effectively a no-op for IPv4 unicast — it is silently ignored with no error message, making this one of the harder faults to spot without reading the config carefully.