BGP AS path prepending---NO EXPORT :)

[Vishal Kolamkar]

Hi All,

Could you please highlight does below route map make sense. We have applied below route-map on bgp nei in live working environmant towards Amazon Services.  As per my knowledge...prefix matched & prepended with AS path...but then set with no--export community(this means route map is not advertising the pefixes at all). Clear my concept on no export...i know it doesent advertise..whts the use of as path prepend with no export community?

!

route-map DEV_INFRA_OUT permit 10
match ip address prefix-lists AWS_VPC_OUT
route-map DEV_INFRA_OUT permit 20
match ip address prefix-lists WAN_SUBNETS_TO_AWS
set as-path prepend 65001 65001 65001 65001
route-map DEV_INFRA_OUT permit 30
match ip address prefix-lists GRW_CP_VPN_POOL
set community no-export
route-map DEV_INFRA_OUT permit 40
match ip address prefix-lists SLG_CP_VPN_POOL
set as-path prepend 65001 65001 65001 65001
set community no-export

!

address-family ipv4 vrf MARPLE_AWS
!
neighbor 169.254.21.137 remote-as 9059
neighbor 169.254.21.137 activate
neighbor 169.254.21.137 timers 10 30 30
neighbor 169.254.21.137 soft-reconfiguration inbound
neighbor 169.254.21.137 route-map DEV_INFRA_IN in
neighbor 169.254.21.137 route-map DEV_INFRA_OUT out

!

[Peter Paluch · Accepted solution]

Vishal,

The no-export community says that the route should not be advertised to eBGP peers, that is, to a different AS.

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-bgp-toc.html#communityattribute

If the neighbor 169.254.21.137 receives a route from you with the no-export community set, it is allowed to advertise this route to any of its iBGP peers, but neither this neighbor nor its iBGP peers are allowed to advertise this route to a neighbor in a different AS.

Would this explain the behavior?

Best regards,
Peter

[Masoud Pourshabanian · Accepted solution]

Hello,

Just adding to Peter's answer.

Your router probably ignores sending that community because you need to tell your router to send it.

Do you have the command below? If you do not have, you router does not send any community.

neighbor 169.254.21.137 send-community.

Masoud

[Vishal Kolamkar]

Yes..i got that..thanks Peter

[Vishal Kolamkar]

Yes..i got that..thanks Peter