Configuring PW Switching

Context

To forward packets through a multi-segment PW, configure PW switching so that PW labels can be exchanged. PW switching must be configured on the Superstratum PE (SPE) where a large number of MPLS LDP sessions can be established.

In the following cases, PW switching is required:

Two PEs are in different ASs, and no signaling connection or tunnel can be set up between the two PEs.
Two PEs use different signaling.
If the access device can run MPLS but does not support a large number of LDP sessions, the User Facing Provider Edge (UFPE) can be used as a UPE and the SPE as a node for switching LDP sessions. The SPE is similar to a signaling reflector.

PW switching supports three modes: static mode, dynamic mode, and mixed mode:

When static PWs are used between the SPE and two connected PEs, configure static PW switching.
When dynamic PWs are used between the SPE and two connected PEs, configure dynamic PW switching.
When a static PW and a dynamic PW are used between the SPE and two connected PEs, configure mixed PW switching.

Pre-configuration Tasks

Before configuring multi-segment PW switching, complete the following tasks:

Enable MPLS L2VPN on PEs.
Configure a static PW on UPEs if PW switching is performed between two static PWs. For details, see Configuring a Static PW.
Configure a dynamic PW on UPEs if PW switching is performed between two dynamic PWs. For details, see Configuring a Dynamic PW.

Procedure

Configuring static PW switching
Perform the following operations on the SPE.
1. Run system-view
  
  The system view is displayed.
2. Run mpls switch-l2vc ip-address vc-id trans trans-label recv received-label [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] between ip-address vc-id trans trans-label recv received-label [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] encapsulation encapsulation-type [ control-word [ cc { alert | cw } ^* cv lsp-ping ] | [ no-control-word ] [ cc alert cv lsp-ping ] ] [ control-word-transparent ]
  
  Static PW switching is configured.
  
  To configure static PW switching, you must configure PW labels on each SPE.
  
  A static multi-segment PW is established as follows:
  - On the UPE, when the AC status is Up and the PSN tunnel exists, the PW status is Up.
  - On the SPE, as long as the PSN tunnels exist on both sides, the PW is in Up state even if the SPE and UPE use different PW encapsulation types.
  It is recommended that you set the same PW encapsulation type by specifying the encapsulation-type parameter on the SPE and UPE to facilitate management.
Configuring dynamic PW switching
Perform the following operations on the SPE.
1. Run system-view
  
  The system view is displayed.
2. Run mpls switch-l2vc ip-address vc-id [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] between ip-address vc-id [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] encapsulation encapsulation-type [ control-word-transparent ]
  
  Dynamic PW switching is configured.
  
  Dynamic PW switching is easy to configure. Two neighboring endpoints (UPE or SPE) will send remote labels to the SPE through signaling. Two UPEs will send the control word and VCCV to the SPE through signaling.
  
  The PW encapsulation type (specified by the encapsulation-type parameter) on the SPE must be the same as that on the UPE. Otherwise, the PW cannot go Up.
Configuring mixed PW switching

When you configure mixed PW switching, ip-address vc-id before between specifies the VC ID of a dynamic PW and ip-address vc-id after between specifies the VC ID of a static PW. The two values cannot be interchanged.

Perform the following operations on the SPE.
1. Run system-view
  
  The system view is displayed.
2. Run mpls switch-l2vc ip-address vc-id [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] between ip-address vc-id trans trans-label recv received-label [ tunnel-policy policy-name ] [ oam-packet pop flow-label ] encapsulation encapsulation-type [ mtu mtu-value ] [ control-word [ cc { alert | cw } ^* cv lsp-ping ] | [ no-control-word ] [ cc alert cv lsp-ping ] ] [ flow-label { both | send | receive } ] [ control-word-transparent ]
  
  Mixed PW switching is configured.
  
  To configure mixed PW switching, configure a PW label for the static PW. The PW encapsulation type (specified by the encapsulation-type parameter) on the SPE must be the same as that on the UPE connected to a dynamic PW.
  
  To configure mixed PW switching, the following MTUs must be the same:
  - Local MTU of the dynamic PW
  - Peer MTU of the dynamic PW
  - Local MTU of the static PW
  - Peer MTU of the static PW
  In mixed PW switching, the MTUs of the interfaces on the two ends must be the same and cannot be greater than 1500 bytes.

Verifying the Configuration

Run the display mpls switch-l2vc [ ip-address vc-id encapsulation encapsulation-type | state { down | up } ] command on the SPE to view information about PW switching.