Introduction to L2TP VPN Address Pool

LNS assigns the IP addresses in the address pool to users. After the client has established a connection to LNS successfully, LNS will choose an IP address along with other related parameters (such as DNS server address, WINS server address, etc) from the address pool, and assigns them to the client.

L2TP provides fixed IP addresses by creating and implementing IP binding rules that consist of static IP binding rule and IP-role binding rule. The static IP binding rule binds the client user to a fixed IP address in the address pool. Once the client has established a connection successfully, the system will assign the binding IP to the client. The IP-role binding rule binds the role to a specific IP range in the address pool. Once the client has established a connection successfully, the system will assign an IP address within the IP range to the client.

When LNS is allocating IP addresses in the address pool, the system will check the IP binding rule and determine how to assign IP addresses for the client based on the specific checking order below:

1. Check if the client is configured with any static IP binding rule. If so, assign the binding IP address to the client; otherwise, further check other configurations. Note if the binding IP address is in use, the user will be unable to log in.
2. Check if the client is configured with any IP-role binding rule. If so, assign an IP address within the binding IP range to the client; otherwise, the user will be unable to log in.

Note: The IP addresses defined in the static IP binding rule and IP-role binding rule should not be overlapped.