PLS. Figure 7-13 depicts two data flows from Host X: one to Y and one to Z. Two LSPs are shown: LSR A is the ingress point into the MPLS network for data from Host X. When it receives packets from X, LSR A determines the FEC for each packet, deduces the LSP to use, and adds a label to the packet. LSR A then forwards the packet on the appropriate interface for the LSR B is an intermediate LSR in the MPLS network. It simply takes each labeled packet and uses the pairing {incoming interface, label value} to decide the pairing {outgoing interface, label value} with which Figure 7-13 Two LSPs in an MPLS packet-switched Host Z network. LSR D Egress LSR A Ingress LSR B Host X LSR C Egress Host Y Chapter 7 Figure 7-14 MPLS is a general-purpose tunneling mechanism MPLS in a nutshell. carries IP and non-IP payloads Source: Cisco. uses label switching to forward packets/cells thru the network can operate over any data-link layer Separates control plane from forwarding plane enables IP control plane to run on devices that cannot understand IP or recognize packet boundaries Control plane IP routing protocols (e.g., OSPF, IS-IS) label distribution protocols (e.g., LDP, RSVP) Forwarding plane label switching on packet/cell basis ATM-LSR IP routers and ATM switches can be Label Switch Routers (LSR) Effort started in 1996 RFCs out in 2001 RFC3031 - MPLS Architecture Packet-LSR to forward the packet. This procedure can use a simple lookup table and can be performed in hardware, along with the swapping of the label value and forwarding of the packet. This enables MPLS networks to be built on existing label-switching hardware such as ATM and Frame Relay. This way of forwarding data packets can be potentially much faster than examining the full packet header to decide the next hop. In the example, each packet with the label value 21 will be dispatched out of the interface toward LSR D, bearing the label value 47. Packets with the label value 17 will be relabeled with the value 11 and sent toward LSR C. LSR C and LSR D act as egress L