Nokia IPSO 4.0 manual Ebgp Multihop Support, 410

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For further details, refer to the confederations specification document (RFC 1965 as of this writing).

RDI A

CBGP

CBGP

RDI C

AS1AS2

RDI B

EBGP

00329

AS1 has seven BGP-speaking routers grouped under different routing domains: RDI A, RDI B, and RDI C. Instead of having a full-mesh connection among all seven routers, you can have a full-meshed connection within just one routing domain.

EBGP Multihop Support

Connections between BGP speakers of different ASes are referred to as EBGP connections. BGP enforces the rule that peer routers for EBGP connections need to be on a directly attached network. If the peer routers are multiple hops away from each other or if multiple links are between them, you can override this restriction by enabling the EBGP multihop feature. TCP connections between EBGP peers are tied to the addresses of the outgoing interfaces. Therefore, a single interface failure severs the session even if a viable path exists between the peers.

EBGP multihop support can provide redundancy so that an EBGP peer session persists even in the event of an interface failure. Using an address assigned to the loopback interface for the EBGP peering session ensures that the TCP connection stays up even if one of the links between them is down, provided the peer loopback address is reachable. In addition, you can use EBGP multihop support to balance the traffic among all links.

410 Nokia Network Voyager for IPSO 4.0 Reference Guide