# LAC Configuration Prerequisites

Before you begin configuring the router as a LAC, perform the following steps:

1. Create a virtual router.
   host1(config)#virtual-router west
2. Assign a router ID IP address, such as that for a loopback interface, to the virtual router. This address must be reachable by the L2TP peer.
   host1:west(config)#ip router-id 10.10.45.3

   | Caution: You must explicitly assign a router ID to a virtual router rather than using a dynamically assigned router ID. A fixed ID is required because every time the ID changes, L2TP must disconnect all existing tunnels and sessions that use the old ID. If you use a dynamically assigned router ID, the value can change without warning, leading to failure of all L2TP tunnels and sessions. Also, the router could dynamically assign a router ID that is not reachable by the L2TP peer, causing a complete failure of L2TP. You must set the router ID even if you specified a source address in the domain map or a local address in the host profile.

3. When configuring the router as a LAC, configure the router or virtual router for Broadband Remote Access Server (B-RAS).

   | Note: If you are using shared tunnel-server ports, you must configure the shared tunnel-server ports before you configure Layer 2 Tunneling Protocol (L2TP) network server (LNS) support. You use the tunnel-server command in Global Configuration mode to specify the physical location of the shared tunnel-server port that you want to configure. See JunosE Physical Layer Configuration Guide for additional information about the tunnel-server command and shared tunnel-server ports.

#### Related Topics

- virtual-router
- ip router-id