H3C Technologies H3C S6800 Series Switches - Manual (Page 14)

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Configuring basic MPLS
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.
In this chapter, the term "interface" refers to a Layer 3 interface. It can be a VLAN interface or a Layer 3
Ethernet interface. Layer 3 Ethernet interfaces refer to the Ethernet interfaces that operate in Layer 3 mode.
For information about switching the Ethernet interface operating mode, see Layer 2—LAN Switching
Configuration Guide.
Overview
MPLS has the following advantages:
• High speed and efficiency—MPLS uses short- and fixed-length labels to forward packets, avoiding
complicated routing table lookups.
• Multiprotocol support—MPLS resides between the link layer and the network layer. It can work over
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.
• TC—3-bit traffic class, used for QoS. It is also called Exp.