Mpls Label Switching And Packet Forwarding - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

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MPLS Label Switching and Packet Forwarding

MPLS is not a routing protocol; it works with layer 3 routing protocols (BGP, IS-IS,
OSPF) to integrate network layer routing with label switching. An MPLS FEC consists
of a set of packets that are all forwarded in the same manner by a given
label-switching router (LSR). For example, all packets received on a particular interface
might be assigned to a FEC. MPLS assigns each packet to a FEC only at the LSR that
serves as the ingress node to the MPLS domain. A label distribution protocol binds
a label to the FEC. Each LSR uses the label distribution protocol to signal its forwarding
peers and distribute its labels to establish an LSP. The label distribution protocol
enables negotiation with the downstream LSRs to determine what labels are used
on the LSP and how they are employed.
Labels represent the FEC along the LSP from the ingress node to the egress node.
The label is prepended to the packet when the packet is forwarded to the next hop.
Each label is valid only between a pair of LSRs. A downstream LSR reached by a
packet uses the label as an index into a table that contains both the next hop and a
different label to prepend to the packet before forwarding. This table is usually
referred to as a label information base (LIB).
The LSR that serves as the egress MPLS node uses the label as an index into a table
that has the information necessary to forward the packet from the MPLS domain.
The forwarding actions at the egress LSR can be any of the following:
RFC 3478 Graceful Restart Mechanism for Label Distribution Protocol (February
2003)
RFC 3479 Fault Tolerance for the Label Distribution Protocol (LDP) (February
2003)
RFC 3564 Requirements for support of Differentiated Services-aware MPLS
Traffic Engineering (July 2003)
RFC 4090 Fast Reroute Extensions to RSVP-TE for LSP Tunnels (May 2005)
RFC 4364 BGP/MPLS IP Virtual Private Networks (VPNs) (February 2006)
RFC 4379 Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures
(February 2006)
RFC 4661 Signaling Requirements for Point-to-Multipoint Traffic-Engineered
MPLS Label Switched Paths (LSPs) (April 2006)
RFC 4875 Extensions to Resource Reservation Protocol - Traffic Engineering
(RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs) (May 2007)
Forward the packet based on the inner header exposed after popping the label.
This can be accomplished either by doing a routing table lookup or forwarding
based on the exposed inner MPLS label.
MPLS Label Switching and Packet Forwarding
Chapter 2: MPLS Overview
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