What are the types of L2VPN

L2VPN intelligence is limited to the provider edge (PE) routers. Therefore, L2VPN is an edge technology—like MPLS VPN—that uses an MPLS backbone.

L2VPN are categorized as

1)      VPWS ( Virtual Private Wan Services)

-          VPWS also known as AToM  or Xconnects

-          AToM is the Cisco name for the Layer 2 transport service over an MPLS backbone

-          VPWS  are Point-to-Point

-          We can connect two distant sites that use different Layer 2 technologies, for example one site uses frame relay and the other uses ATM.

-          Distant sites that can use any of these technologies: Frame-Relay, PPP, Ethernet, ATM, that's why xconnects are also called Any Transport over MPLS (AToM).

2)    VPLS ( Virtual Private Lan Services)

-          VPLS can be Point-to-Point (linking only 2 sites) and can be Multipoint (linking multiple sites together)

-          VPLS can only link Ethernet sites.

What if the Core of the Service Provider is IP based only.How can we transport L2 frames across this infrastructure? L2TPv3 is the Layer 2 transport service over an IP network. The Layer 2 frames are encapsulated with an L2TPv3 header and are transported across the IP network. Similar to AToM, L2TPv3 can carry ATM, Frame Relay, HDLC, PPP, Ethernet, ATM, and others.

What are advantages of MPLS?

Main Benefit of MPLS - BGP Free CORE

When the IP network of a service provider must forward traffic, each router must look up the destination IP address of the packet. If the packets are sent to destinations that are external to the service provider network, those external IP prefixes must be present in the routing table of each router. BGP carries external prefixes, such as the customer prefixes or the Internet prefixes. This means that all routers in the service provider network must run BGP.MPLS, however, enables the forwarding of packets based on a label lookup rather than a lookup of the IP addresses. MPLS enables a label to be associated with an egress router rather than with the destination IP address of the packet. The label is the information attached to the packet that tells every intermediate router to which egress edge router it must be forwarded. The core routers no longer need to have the information to forward the packets based on the destination IP address. Thus, the core routers in the service provider network no longer need to run BGP. The router at the edge of the MPLS network still needs to look at the destination IP address of the packet and hence still needs to run BGP. Each BGP prefix on the ingress MPLS routers has a BGP next-hop IP address associated with it. This BGP next-hop IP address is an IP address of an egress MPLS router. The label that is associated with an IP packet is the label that is associated with this BGP next-hop IP address. Because every core router forwards a packet based on the attached MPLS label that is associated with the BGP next-hop IP address, each BGP next-hop IP address of an egress MPLS router must be known to all core routers. Any interior gateway routing protocol, such as OSPF or ISIS, can accomplish this task . An Internet service provider (ISP) that has 200 routers in its core network needs to have BGP running on all 200 routers. If MPLS is implemented on the network, only the edge routers—which might be 50 or so routers—need to run BGP. All routers in the core of the network are now forwarding labeled packets, without doing an IP lookup, so they are now relieved from the burden of running BGP. Because the full Internet routing table is well above 150,000 routes, not having to run BGP on all routers is a serious consideration. Routers without the full Internet routing table need a lot less memory. You can run the core routers without the complexity of having to run BGP on them.