H3C Technologies H3C S12500-X Series Switches - Manual (Page 14)

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An MPLS network comprises the following types of LSRs:
• Ingress LSR—Ingress LSR of packets. It labels packets entering into the MPLS network.
• Transit LSR—Intermediate LSRs in the MPLS network. The transit LSRs on an LSP forward packets to
the egress LSR according to labels.
• Egress LSR—Egress LSR of packets. It removes labels from packets and forwards the packets to their
destination networks.
LSP establishment
LSPs include static and dynamic LSPs.
• Static LSP—To establish a static LSP, you must configure an LFIB entry on each LSR along the LSP.
Establishing static LSPs consumes fewer resources than establishing dynamic LSPs, but static LSPs
cannot automatically adapt to network topology changes. Therefore, static LSPs are suitable for
small-scale networks with simple, stable topologies.
• Dynamic LSP—Established by a label distribution protocol (also called an MPLS signaling protocol).
A label distribution protocol classifies FECs, distributes FEC-label mappings, and establishes and
maintains 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 MP-BGP and RSVP-TE.
In this document, the term "label distribution protocols" refers to all protocols for label distribution. The
term "LDP" refers to the RFC 5036 LDP.
A dynamic LSP is established in the following steps:
1. A downstream LSR classifies FECs according to destination addresses.
2. The downstream LSR assigns a label for each FEC, and distributes the FEC-label binding to its
upstream LSR.
3. The upstream LSR establishes an LFIB entry for the FEC according to the binding information.
After all LSRs along the LSP establish an LFIB entry for the FEC, a dynamic LSP is established for the
packets of this FEC.
Figure 4 Dynamic LSP establishment