Prerequisites: CCNP level skills.
BGP Default Communities
- internet - Advertise this route to the Internet community. All routers belong to it.
- no-export - Do not advertise this route to eBGP peers (real BGP peers).
- no-advertise - Do not advertise this route to any peer (internal or external).
- local-as - Do not advertise this route to peers outside the local autonomous system. This route will not be advertised to other autonomous systems or sub-autonomous systems when confederations are configured.
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfbgp.html#wp1001855
Notice!
AS 13 is a confederation autonomous system. It has two sub-autonomous systems: 65001 and 65003.
Topology
Pic. 1 - Topology Diagram.
Icons designed by: Andrzej Szoblik - http://www.newo.pl
Task 1
On R5 advertises 172.16.105.0/24 so that neither AS 20 nor AS 40 receive it. Do not configure any filtering in AS 13.
Solution
Task 1
On R5 advertises 172.16.105.0/24 so that neither AS 20 nor AS 40 receive it. Do not configure any filtering in AS 13.
Pic. 2 - State Before Configuration Applied (R1).
Pic. 3 - State Before Configuration Applied (R2).
Pic. 4 - State Before Configuration Applied (R4).
R5 Configuration:
!
ip prefix-list L0 seq 5 permit 172.16.105.0/24
!
route-map SET_COMMUNITY permit 10
match ip address prefix-list L0
set community no-export
!
route-map SET_COMMUNITY permit 999
!
router bgp 50
no synchronization
bgp router-id 172.16.105.5
bgp log-neighbor-changes
network 172.16.105.0 mask 255.255.255.0
neighbor 10.1.35.3 remote-as 13
neighbor 10.1.35.3 send-community
neighbor 10.1.35.3 route-map SET_COMMUNITY out
no auto-summary
!
route-map SET_COMMUNITY permit 10
match ip address prefix-list L0
set community no-export
!
route-map SET_COMMUNITY permit 999
!
router bgp 50
no synchronization
bgp router-id 172.16.105.5
bgp log-neighbor-changes
network 172.16.105.0 mask 255.255.255.0
neighbor 10.1.35.3 remote-as 13
neighbor 10.1.35.3 send-community
neighbor 10.1.35.3 route-map SET_COMMUNITY out
no auto-summary
!
R3 Configuration:
!
router bgp 65003
no synchronization
bgp router-id 172.16.103.3
bgp log-neighbor-changes
bgp confederation identifier 13
bgp confederation peers 65001
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.13.1 remote-as 65001
neighbor 10.1.13.1 next-hop-self
neighbor 10.1.13.1 send-community
neighbor 10.1.23.2 remote-as 20
neighbor 10.1.35.5 remote-as 50
no auto-summary
no synchronization
bgp router-id 172.16.103.3
bgp log-neighbor-changes
bgp confederation identifier 13
bgp confederation peers 65001
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.13.1 remote-as 65001
neighbor 10.1.13.1 next-hop-self
neighbor 10.1.13.1 send-community
neighbor 10.1.23.2 remote-as 20
neighbor 10.1.35.5 remote-as 50
no auto-summary
!
Apply 'clear ip bgp * out'
Verification:
Pic. 5 - BGP Table on R1.
Pic. 6 - Detailed BGP Prefix on R1.
R3 received (and passed on) the community no-export to R1. Prefixes with this community cannot be advertised to eBGP peers! R2 and R4 no longer receive 172.16.105.0/24 like shown below:
Pic. 7 - BGP Table on R2.
Pic. 8 - Missing Prefix on R4.
