# LNS Configuration Prerequisites

Before you begin configuring the router as an LNS, 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.

#### Related Documentation

- virtual-router
- ip router-id