
Configuring IP Services
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Interior BGP in Intra-AS Routing
Bay Networks implements Interior BGP (IBGP) intra-AS routing. Under IBGP,
each router in the AS runs an interior gateway protocol (IGP) for internal routing
updates and also maintains an IBGP connection to each BGP border router. The
IBGP information is used in conjunction with the IGP route to the authoring BGP
border router to determine the next hop to use for external networks.
No BGP information is carried by the IGP. Each router uses IBGP exclusively to
determine reachability to external networks. When an IBGP update for a network
is received, it can be passed on to IP for inclusion in the forwarding tables only if
a viable IGP route to the correct border gateway is available.
IBGP in a Transit AS
An AS with more than one BGP speaker can use IBGP to provide a transit service
for networks outside the AS. An AS that provides such a service for BGP speakers
is known as a transit AS (Figure 8-2).
Figure 8-2. Transit Autonomous System
AS 20
AS 10
AS 50
AS 11
AS 12
AS 30
IGP
BGP A
BGP B
BGP C
IP0021A
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