Chapter 10: BGP Configuration Guide
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DIGITAL GIGAswitch/Router User Reference Manual
An IGP, like OSPF, could possibly be used instead of IBGP to exchange routing
information between EBGP speakers within an AS. However, injecting full Internet routes
(50,000+ routes) into an IGP puts an expensive burden on the IGP routers. Additionally,
IGPs cannot communicate all of the BGP attributes for a given route. It is, therefore,
recommended that an IGP not be used to propagate full Internet routes between EBGP
speakers. IBGP should be used instead.
IBGP Routing Group Example
An IBGP Routing group uses the routes of an interior protocol to resolve forwarding
addresses. An IBGP Routing group will determine the immediate next hops for routes by
using the next hop received with a route from a peer as a forwarding address, and using
this to look up an immediate next hop in an IGP’s routes. Such groups support distant
peers, but need to be informed of the IGP whose routes they are using to determine
immediate next hops. This implementation comes closest to the IBGP implementation of
other router vendors.
You should use the IBGP Routing group as the mechanism to configure the GSR for IBGP.
If the peers are directly connected, then IBGP using group-type Internal can also be used.
Note that for running IBGP using group-type Routing you must run an IGP such as OSPF
to resolve the next hops that come with external routes. You could also use protocol
any
so
that all protocols are eligible to resolve the BGP forwarding address.
