6.2 PWE3 Features Supported by the S7700
PWE3 can be classified into the static PW and dynamic PW based on implementation schemes,
and can be classified into the single-hop PW and multi-hop PW based on networking types.
You need to know the following terms defined in the RFC before you read this section:
l Ultimate PE (U-PE): is a PE to which an AC is bound. A U-PE is the first or last PE of an
MH-PW.
l Switching Point PE (S-PE): is a PE that switches PW labels in an MH-PW. An S-PE
establishes and manages PW segments with other S-PEs or U-PEs. A PW segment is a
static or dynamically configured PW established between a pair of PEs. This pair of PEs
can be two U-PEs, two S-PEs, or one U-PE and one S-PE.
PW is classified based on:
l Implementation mechanism: Static PW and Dynamic PW
l Networking model: SH-PW and MH-PW
Static PW and Dynamic PW
l Static PW
A Static PW negotiates parameters without any signaling protocol. You must specify the
relevant information manually.
l Dynamic PW
– A Dynamic PW is a PW that is established by using a signaling protocol.
– A U-PE switches VC labels and binds the corresponding CE through a VC ID. A VC
can be established only when the tunnel between two PEs is successfully set up and
label interchanging and binding are completed.
– The LDP-PW uses LDP as the signaling protocol to send PW messages. The LDP-PW
requires switching PWs to complete the MH-PW.
– The tunnel used to set up an LDP PW can be an LDP LSP, a CR-LSP, or a GRE tunnel.
By default, an LDP LSP is used.
– LDP-PW messages include:
– Request: is used to request label distribution.
– Mapping: is used to distribute labels to the remote PE (U-PE or S-PE). The state bit
is sent to the remote PE by using a Mapping message. Whether to carry the state bit
or not depends on the configuration. By default, the Martini mode does not carry
state bit.
– Notification: is used to announce and negotiate the PW state to reduce messages.
– Withdraw: is used to ask the peer to remove labels. (It carries labels and state
information.)
– Release: is used as a response to a Withdraw message. It is used to ask the peer that
sends a Withdraw message to remove labels.
Figure 6-2 shows the packet exchanges during the establishment, maintenance, and
dismantlement of an LDP PW.
Quidway S7700 Smart Routing Switch
Configuration Guide - VPN 6 PWE3 Configuration
Issue 01 (2011-07-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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