Cisco ASR 9000 Series Routers : Service Providers Edge to Edge VPLS Configuration

Today I am going to talk about the VPLS configuration on Cisco ASR 9000 series routers. Before we will start with the configuration part, lets talk about the basics of the VPLS.

VPLS stands for Virtual Private LAN Service and enables geographically separated local-area network (LAN) segments to be interconnected as a single bridged domain over an MPLS network. So with the help of VPLS customer can extend the Layer 2 traffic across the globe on MPLS enabled service provider network. 

If customer wants to share the L3 information with the service provider to route it from their networks towards the remote site, then we can use routing at the edges of the PE routers and MPLS in the core while if customer don't want to share the L3 information with the service provider they always go with the VPLS type of services where we have L2 protocols like Frame-Relay, Ethernet, ATM services at the edges of the PE routers and MPLS on the core. 

This is the basic difference between the MPLS and VPLS technologies. Some times you saw like EoMPLS ( Ethernet over MPLS) which is another VPLS technology as Layer 2 ethernet information shared over the MPLS.

Fig 1.1- MPLS + VPLS Network Design

Here in the VPLS we are using the bridge domains where data frames are switched within a bridge domain based on the destination MAC address. Multicast, broadcast, and other unknown destination unicast frames are flooded within the bridge domain. 

The source MAC address learning is performed on all incoming frames on a bridge domain. A learned address is aged out. Incoming frames are mapped to a bridge domain, based on either the ingress port or a combination of both an ingress port and a MAC header field.

Use of the pseudowire in VPLS
A pseudo-wire in the VPLS is a point-to-point connection between PE routers which shows tunneling between them. Its primary function is to emulate services like Ethernet over an underlying core MPLS network through encapsulation into a common MPLS format. 

By encapsulating services into a common MPLS format, a pseudowire allows carriers to converge their services to an MPLS network.

VFI- Virtual Forwarding Instance
Now Lets talk about the major component of the VPLS services and is called as VFI. So VFI is a virtual bridge port that is capable of performing native bridging functions, such as forwarding, based on the destination MAC address, source MAC address learning and aging, and so forth.

Make sure you always remember that a VFI is created on the PE router for each VPLS instance. The PE routers make packet-forwarding decisions by looking up the VFI of a particular VPLS instance. It acts like a virtual bridge for a given VPLS instance and has one attachment circuit belonging to a given VPLS are connected to the VFI. 

The PE router establishes emulated VCs to all the other PE routers in that VPLS instance and attaches these emulated VCs to the VFI. Packet forwarding decisions are based on the data structures maintained in the VFI.

Below is the basic configurations on the PE routers, taking into account that with the MPLS domain we have 3 PE routers which is connected to remote sites and we are enabling VPLS services between these PE routers as :