configuration. If dynamic capability negotiation was not negotiated for the session,
the session is bounced automatically.
■ If you issue the deprecated-dynamic-capability-negotiation,
dynamic-capability-negotiation, four-octet-as-numbers, negotiation, or orf
keywords, the command takes effect immediately and bounces the session.
■ If the BGP speaker receives a capability message for a capability that BGP did
not previously advertise in the dynamic capability negotiation capability, BGP
sends a notification to the peer with the error code “ capability message error”
and error subcode “ unsupported capability code.”
■ IPv6 ORF prefix lists are not supported. Therefore you can specify an IPv6 address
with the orf keyword only within the IPv4 address family and when you want
to advertise IPv4 routes to IPv6 peers.
■ Example
host1(config-router)#neighbor 10.6.2.5 capability orf prefix-list both
■ Use the no version to prevent advertisement of the specified capability or use
the negotiation keyword with the no version to prevent all capability negotiation
with the specified peer. Use the default version to restore the default, advertising
the capability.
■ See neighbor capability.
Interactions Between BGP and IGPs
Interactions between BGP and an interior gateway protocol are more likely to occur
in an enterprise topology than in a service provider topology. You can also encounter
interactions when configuring small test topologies. The main interaction factors are
the following:
■ Synchronization between BGP and IGPs
■ Administrative distances for routes learned from various sources
Synchronizing BGP with IGPs
In Figure 36 on page 134, AS 100 provides transit service but does not run BGP on
all of the routers in the AS. In this situation, you must redistribute BGP into the IGP
so that the non-BGP routers—for example, router Albany—learn how to forward
traffic to customer prefixes. If BGP converges faster than the IGP, a prefix might be
advertised to other ASs before that prefix can be forwarded.
For example, suppose router LA advertises a route to router Boston using EBGP, and
router Boston propagates that route to router NY using IBGP. If router NY propagates
the route to router Chicago before the IGP within AS 100 has converged—that is,
before router Albany learns the route—then router Chicago might start sending traffic
for that route before router Albany can forward that traffic.
Interactions Between BGP and IGPs ■ 133
Chapter 1: Configuring BGP Routing
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