Another possible PE-CE routing protocol is IS-IS, which is a link state routing protocol like OSPF. Unlike OSPF, however, IS-IS runs directly over Layer 2, not over IP. Having IS-IS run across the PE–CE link requires ISIS to be VRF aware on the PE routers. You can configure ISIS for a VRF by using the command vrf vrf-name under the IS-IS process. IS-IS processes on a router are differentiated from each other by the tag as configured with the command router isis process-tag. You have to associate the PE-CE link with the correct IS-IS VRF process with the interface command ip router isis process-tag. As with OSPF, each VRF instance has its own IS-IS routing process (and SPF algorithm), IS-IS database, and routing table.

The up/down bit performs ...

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