Configuring Basic Mpls; Overview; Basic Concepts - HP MSR2000 Configuration Manual

Configuring basic MPLS

In this chapter, "MSR2000" refers to MSR2003. "MSR3000" collectively refers to MSR3012, MSR3024,
MSR3044, MSR3064. "MSR4000" collectively refers to MSR4060 and MSR4080.

Overview

Multiprotocol Label Switching (MPLS) provides connection-oriented label switching over connectionless IP
backbone networks. It integrates both the flexibility of IP routing and the simplicity of Layer 2 switching.
MPLS has the following advantages:
High speed and efficiency—MPLS uses short- and fixed-length labels to forward packets, avoiding
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complicated routing table lookups.
Multiprotocol support—MPLS resides between the link layer and the network layer. It can work over
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various link layer protocols (for example, PPP, ATM, frame relay, and Ethernet) to provide
connection-oriented services for various network layer protocols (for example, IPv4, IPv6, and IPX).
• Good scalability—The connection-oriented switching and multilayer label stack features enable
MPLS to deliver various extended services, such as VPN, traffic engineering, and QoS.

Basic concepts

FEC
MPLS groups packets with the same characteristics (such as packets with the same destination or service
class) into a forwarding equivalence class (FEC). Packets of the same FEC are handled in the same way
on an MPLS network.
Label
A label uniquely identifies an FEC and has local significance.
Figure 1 Format of a label
A label is encapsulated between the Layer 2 header and Layer 3 header of a packet. It is four bytes long
and consists of the following fields:
Label—20-bit label value.
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TC—3-bit traffic class, used for QoS. It is also called Exp.
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S—1-bit bottom of stack flag. A label stack can contain multiple labels. The label nearest to the
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Layer 2 header is called the top label, and the label nearest to the Layer 3 header is called the
bottom label. The S field is set to 1 if the label is the bottom label and set to 0 if not.
TTL—8-bit time to live field used for routing loop prevention.
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