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Creating Labels per FEC

By default, the router minimizes the number of stacked labels to be managed by generating a single label for all BGP routes advertised by a given VRF; this is a per-VRF label. Upon receiving traffic for a per-VRF label, the router performs a label pop and a route lookup to forward the traffic to the next hop.

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.
Examplehost1: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.

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