You can use the ip mpls forwarding-mode label-switched command to configure
the router to generate a label for each different FEC that a BGP route points to in the
VPN; this is a per-FEC label. Issuing this command enables you to avoid a route
lookup for traffic destined for CE routers, because in this mode traffic is label switched
to the corresponding next hop over that interface; a route lookup is not performed.
The route for which a label is allocated can be an ECMP route; in that case, the
label-switched traffic uses ECMP.
For the following types of routes, the router always generates a per-VRF label and
forwards traffic after a route lookup (rather than label switching the traffic without
a route lookup) regardless of the status of this command:
■ Local connected interfaces redistributed into BGP, regardless of the interface
type.
■ BGP redistributed routes that point to loopback interfaces.
The following commands configure a router where BGP is running in VRF pe11 and
static and connected routes are redistributed into the VRF:
host1(config)#ip vrf pe11
host1(config-vrf)#ip mpls forwarding-mode label-switched
host1(config-vrf)#ip route vrf pe11 10.3.4.5 255.255.255.255 fastEthernet 0/1
host1(config-vrf)#ip route vrf pe11 10.1.1.1 255.255.255.255 loopback 1
host1(config-vrf)#exit
host1(config)#router bgp 100
host1(config-router)#address-family ipv4 unicast vrf pe11
host1(config-router-af)#exit
host1(config-router)#no auto-summary
host1(config-router)#no synchronization
host1(config-router)#redistribute static
host1(config-router)#redistribute connected
For each connected route that is redistributed into the VRF and advertised across
the BGP/MPLS VPN, the router assigns a per-VRF label rather than a per-FEC label.
The static route 10.1.1.1/32 points to loopback interface 1. BGP therefore advertises
this static route with a per-VRF label.
ip mpls forwarding-mode label-switched
■ Use to generate a label for each different FEC pointed to by a BGP route.
■ For some types of routes, issuing this command has no effect on the labels
created; they are always per-VRF labels.
■ Example
host1:vr1(config-vrf)#ip mpls forwarding-mode label-switched
■ Use the no version to restore the default, generating a single label for all BGP
routes sent from a given VRF.
■ See ip mpls forwarding-mode label-switched.
Configuring BGP VPN Services ■ 439
Chapter 5: Configuring BGP-MPLS Applications
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