BGP: Communities: No-Export
· In BGP, communities are basically used to tag the routes so that we can filter them where ever we want.
· NO-EXPORT is a special community value. It simply instructs the received router not to forward this route outside the AS.
R1-------------------R2--------------------R3
· R1: AS 100
· R2: AS 200
· R3: AS 300
· R1 is advertising a prefix 1.1.1.1/32 to R2 with no-export community
· R2 will not forward this prefix to R3.
· Let me configure it and see…
R1#show run | begin router bgp
router bgp 100
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 11.11.11.11 mask 255.255.255.255
neighbor 100.1.12.2 remote-as 200
neighbor 100.1.12.2 send-community
neighbor 100.1.12.2 route-map NO-EXPORT out
no auto-summary
!
!
!
ip prefix-list 1 seq 5 permit 1.1.1.1/32
!
route-map NO-EXPORT permit 10
match ip address prefix-list 1
set community no-export
!
route-map NO-EXPORT permit 100
!
R2#show run | begin router bgp 200
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 100.1.12.1 remote-as 100
neighbor 100.1.23.3 remote-as 300
neighbor 100.1.23.3 send-community
no auto-summary
!
R3#show run | begin router bgp 300
router bgp 300
no synchronization
bgp log-neighbor-changes
neighbor 100.1.23.2 remote-as 200
no auto-summary
!
R1#show ip bgp
BGP table version is 3, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 11.11.11.11/32 0.0.0.0 0 32768 i
R1#
R2#show ip bgp
BGP table version is 3, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 100.1.12.1 0 0 100 i
*> 11.11.11.11/32 100.1.12.1 0 0 100 i
R2#
R3#show ip bgp
BGP table version is 2, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 11.11.11.11/32 100.1.23.2 0 200 100 i
R3#
R2#show ip bgp 1.1.1.1
BGP routing table entry for 1.1.1.1/32, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
Not advertised to any peer
100
100.1.12.1 from 100.1.12.1 (1.1.1.1)
Origin IGP, metric 0, localpref 100, valid, external, best
Community: no-export
R2#
Observations:
· R1 advertised 1.1.1.1/32 into BGP with no-export community.
· R2 got the route and it didn’t forward it to R3 since R3 is in different AS.
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