Example: Configuring a Fallback Global Option

For the second solution you use the fallback global option on the PE–CE IP interface (Figure 103). If you have configured this option, the PE router simultaneous performs two different lookups when a packet arrives from the CE router. One lookup is in the IP routing table of the VRF; the other lookup is in the IP routing table of the parent VR.

Figure 103: Fallback Global Option

Fallback Global Option

If BGP finds a route in the VRF context, it uses that route. If BGP does not find a route in the VRF context but does find a route in the VR context, it falls back on the global route in the parent VR. BGP drops the packet if it does not find a route in either context.

To enable fallback global on a PE-CE IP interface:

host1:pe1(config)#interface atm2/0.11 host1:pe1(config-if)#ip vrf forwarding pe11 fallback global host1:pe1:pe11(config-if)#atm pvc 11 0 11 aal5snap host1:pe1:pe11(config-if)#ip address 10.11.11.1 255.255.255.0 host1:pe1:pe11(config-if)#exit

See Configuring Secondary Routing Table Lookup for more information.

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