Configuring IS-IS SR to Communicate with LDP

This section describes how to configure IS-IS SR to communicate with LDP.

Usage Scenario

The SR and LDP interworking technique allows both segment routing and LDP to work within the same network. This technique connects an SR network to an LDP network to implement MPLS forwarding.

On the network shown in Figure 1, an SR domain is created between PE1 that functions as a mapping client and the P device that functions as a mapping server. Mappings between prefixes and SIDs need to be configured on the P device and advertised to PE1, which receives the mappings. An LDP domain lies between the P device and PE2, which supports only LDP. To enable PE1 and PE2 to communicate with each other, you need to establish an SR LSP and an LDP LSP, and establish the mapping between the SR LSP and LDP LSP on the P device.

Figure 1 Communication between SR and LDP

Pre-configuration Tasks

Before you configure IS-IS SR to communicate with LDP, complete the following tasks:

Configure an SR LSP from PE1 to the P. See Configuring an IS-IS SR-MPLS BE Tunnel.
Configure an LDP LSP from the P to PE2. See Configuring an LDP LSP.

Procedure

Configure the mapping server.
1. Run system-view
  The system view is displayed.
2. Run segment-routing
  Segment routing is globally enabled, and the Segment Routing view is displayed.
3. Run mapping-server prefix-sid-mapping ip-address mask-length begin-value [ range range-value ] [ attached ]
  Mapping between the prefix and SID is configured.
4. Run quit
  Exist the SR view.
5. Run isis [ process-id ]
  The IS-IS view is displayed.
6. Run segment-routing mapping-server send
  The local node is enabled to advertise the local SID label mapping.
7. (Optional) Run segment-routing mapping-server receive
  The local node is enabled to receive SID label mapping messages.
8. Run commit
  The configuration is committed.
(Optional) Configure the mapping client.
A device that is not configured as a mapping server functions as a mapping client by default.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run segment-routing mapping-server receive
  The local node is enabled to receive SID label mapping messages.
4. Run commit
  The configuration is committed.
Configure the device connecting the LDP domain and the SR domain.
1. Run system-view
  The system view is displayed.
2. Run mpls
  The MPLS view is displayed.
3. Run lsp-trigger segment-routing-interworking best-effort host
  A policy for triggering backup LDP LSP establishment is configured.
4. Run commit
  The configuration is committed.

Checking the Configurations

After completing the configurations, run the display segment-routing prefix mpls forwarding command to check the label forwarding information base of Segment Routing.