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Feature Description - VPN 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - VPN
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LDP VPLS

LDP VPLS

Background

LDP VPLS, also called Martini VPLS, uses a static discovery mechanism to discover VPLS members using LDP signaling. VPLS information is carried in extended TLV fields (type 128 and type 129 FEC TLVs) of LDP signaling packets. Here, FEC stands for forwarding equivalence class. During the establishment of a PW, the label distribution mode is downstream unsolicited (DU) and the label retention mode is liberal.

Related Concepts

LDP VPLS involves the following concepts:

  • FEC: A set of packets with similar or identical characteristics and forwarded in the same way by LSRs. Characteristics determining the FEC of a packet include the destination address, service type, and QoS attribute.

  • TLV: A highly efficient and expansible coding mode for protocol packets. To support new features, you only need to add new types of TLVs to carry information required by the features.

  • DU: A label distribution mode in which a label switching router (LSR) distributes labels to FECs without having to receive Label Request messages from its upstream LSR.

  • Liberal: A label retention mode in which an LSR retains the label mapping received from a neighboring LSR, regardless of whether the neighboring LSR is its next hop. In liberal label retention mode, an LSR can use the labels sent from neighboring LSRs that are not at the next hop to re-establish an LSP. This mode requires more memory and label space than the conservative mode.

Implementation Process

Figure 8-8 shows the process of establishing a PW using LDP signaling.

Figure 8-8 Establishing a PW using LDP signaling

  • After PE1 is associated with a VSI, and PE2 is configured as a peer of PE1, PE1 sends a Label Mapping message to PE2 in DU mode if an LDP session exists between PE1 and PE2. The Label Mapping message carries information required to establish a PW, such as the PW ID, VC label, and interface parameters.
  • Upon receipt, PE2 checks whether itself has been associated with the VSI. If PE2 has been associated with the VSI and PW parameters on PE1 and PE2 are consistent, PE1 and PE2 belong to the same VSI. In this case, PE2 establishes a unidirectional VC named VC1 immediately after PE2 receives the Label Mapping message. Meanwhile, PE2 sends a Label Mapping message to PE1. After receiving the message, PE1 takes a sequence of actions similar to those taken by PE2 and establishes VC2.

Figure 8-9 shows the process of tearing down a PW using LDP signaling.

Figure 8-9 Tearing down a PW using LDP signaling

  • After the peer configuration about PE2 is deleted from PE1, PE1 sends a Label Withdraw message to PE2. After receiving the Label Withdraw message, PE2 withdraws its local VC label, tears down VC1, and sends a Label Release message to PE1.
  • After receiving the Label Release message, PE1 withdraws its local VC label and tears down VC2.

Usage Scenario

The LDP mode applies to VPLS networks that do not have many sites, do not span multiple ASs, or with PEs that do not run BGP.

Benefits

LDP VPLS offers the following benefits:

  • Easy configuration
  • Label resource saving
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Updated: 2019-01-14

Document ID: EDOC1100058940

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