Mpls Overview; Operation Of Mpls Ip Vpn - Avaya 8800 Planning And Engineering

MPLS IP VPN and IP VPN Lite

MPLS overview

Multi-Protocol Label Switching (MPLS) (RFC3031) is primarily a service provider technology
where IP traffic can be encapsulated with a label stack and then label switched across a
network through Label Switched Routers (LSR) using Label Switched Paths (LSP). An LSP is
an end-to-end unidirectional tunnel set up between MPLS-enabled routers. Data travels
through the MPLS network over LSPs from the network ingress to the network egress. The
LSP is determined by a sequence of labels, initiated at the ingress node. Packets that require
the same treatment for transport through the network are grouped into a forwarding
equivalence class (FEC).
The following figure shows a sample MPLS network.
Figure 97: Label Switched Path and Forwarding Equivalent Class
The FECs are identified by the destination subnet of the packets to be forwarded. All packets in
the same FEC use the same LSP to travel across the network. Packets are classified once,
as they enter the network; all subsequent forwarding decisions are based on the FEC to which
each packet belongs (that is, each label corresponds to a FEC).

Operation of MPLS IP VPN

MPLS IP-VPN enabled routers use two labels as shown in the following figure. The Avaya
Ethernet Routing Switch 8800/8600 uses LDP for IP VPN. LDP generates and distributes an
outer label referred as a tunnel label, which is in fact the LSP. BGP-MP generates and
distributes the inner label referred to as the VPN label.
218 Planning and Engineering — Network Design November 2010