The BGP loop-prevention mechanism does not allow a BGP speaker to accept prefixes with the local AS number in the AS_PATH list. However, in some cases, it would be desirable to accept the routes originated in the same AS via another AS.
- The company’s network is partitioned, and every partition connects to the Internet or ISP
- The company connects to an ISP and network becomes segmented due to an emergency. In this case, the prefixes advertised to the ISP must be accepted back by the border peers.
Currently we have multiple paths to learn 3.3.3.0/24 prefix on R2, but due to the loop-prevention mechanism the AS containing same prefix learned having local AS in path are not allowed.
We will configure R2 to allow the prefixes having local AS in path attribute.
R2#show run | s bgp
router bgp 123
no synchronization
bgp log-neighbor-changes
network 2.2.2.0 mask 255.255.255.0
neighbor 12.1.1.1 remote-as 123
neighbor 12.1.1.1 next-hop-self
neighbor 24.1.1.4 remote-as 400
neighbor 24.1.1.4 send-community
neighbor 24.1.1.4 allowas-in
no auto-summary
ip bgp-community new-format
- The company’s network is partitioned, and every partition connects to the Internet or ISP
- The company connects to an ISP and network becomes segmented due to an emergency. In this case, the prefixes advertised to the ISP must be accepted back by the border peers.
Currently we have multiple paths to learn 3.3.3.0/24 prefix on R2, but due to the loop-prevention mechanism the AS containing same prefix learned having local AS in path are not allowed.
We will configure R2 to allow the prefixes having local AS in path attribute.
R2#show run | s bgp
router bgp 123
no synchronization
bgp log-neighbor-changes
network 2.2.2.0 mask 255.255.255.0
neighbor 12.1.1.1 remote-as 123
neighbor 12.1.1.1 next-hop-self
neighbor 24.1.1.4 remote-as 400
neighbor 24.1.1.4 send-community
neighbor 24.1.1.4 allowas-in
no auto-summary
ip bgp-community new-format
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