H3C Technologies H3C SR8800 - Manual (Page 14)

3
Structure of the MPLS network
Figure 3 Diagram for the MPLS network structure
As shown in Figure 3 , the element of an MPLS network is LSR. LSRs in the same routing or administrative
domain form an MPLS domain.
An MPLS domain consists of the following types of LSRs:
• Ingress LSRs for receiving and labeling packets coming into the MPLS domain.
• Transit LSRs for forwarding packets along LSPs to their egress LERs according to the labels.
• Egress LSRs for removing labels from packets and IP forwarding the packets to their destination
networks.
In other words, transit LSRs perform MPLS forwarding based on labels of packets, and the ingress and
egress LSRs deal with the switchover between MPLS and IP forwarding.
LSP establishment and label distribution
LSP establishment
Establishing LSPs is to bind FECs with labels on each LSR involved and notify its adjacent LSRs of the
bindings, so as to establish the LFIB on each LSR. LSPs can be established through manual configuration,
or be established dynamically through label distribution protocols.
1. Establishing a static LSP through manual configuration
To establish a static LSP, you need to assign a label to the FEC on each LSR along the packet
forwarding path. Establishment of static LSPs consumes fewer resources than dynamic LSP
establishment. However, static LSPs cannot adapt to network topology changes. Therefore, static
LSPs are suitable for small-scale networks with simple, stable topologies.
2. Establishing an LSP through a label distribution protocol
Label distribution protocols are MPLS signaling protocols. They can classify FECs, distribute labels,
and establish and maintain LSPs. Label distribution protocols include protocols designed
specifically for label distribution, such as the Label Distribution Protocol (LDP), and protocols
extended to support label distribution, such as BGP and RSVP-TE.
This document discusses LDP only. For more information about LDP, see “ LDP .”