Layer 2.5 VPNs use essentially the
same configuration format as Layer 2 VPNs. You should already have
experience configuring Layer 2 VPNs before you attempt to configure
a Layer 2.5 VPN. The major steps required to create a Layer 2
VPN are:
Enable MPLS on interfaces pointing toward the core and
the edge on your provider edge (PE) and provider core (P) routers.
Configure Label Distribution Protocol (LDP) on all P and
PE routers for traffic traveling from the PEs, through the core, and
to the remote PEs.
Establish an internal BGP (IBGP) Layer 2 VPN peering relationship
between PE routers.
Set up policies on your PE routers that will set a private
community tag on outbound BGP traffic heading to the remote PEs and
accept incoming traffic that matches similar community traffic from
the remote PEs.
Build VPN routing and forwarding (VRF) instances on your
PE routers and apply the previously configured policies to deliver
private traffic to the customer edge (CE) routers.
