DHCP and Routing and Remote Access

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When the Routing and Remote Access service is configured to use DHCP to obtain IP addresses, the Routing and Remote Access service instructs the DHCP client component to obtain 10 IP addresses from a DHCP server. The Routing and Remote Access service uses the first IP address obtained from DHCP for the RAS server interface, and subsequent addresses are allocated to TCP/IP-based remote access clients as they connect. IP addresses freed due to remote access clients disconnecting are reused.

When all 10 IP addresses are used, the Routing and Remote Access service uses the DHCP client component to obtain 10 more. You can modify the number of IP addresses obtained at a time by changing the value of the InitialAddressPoolSize registry entry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\ RemoteAccess \Parameters\Ip

With the Windows NT 4.0 remote access server, the DHCP allocated addresses are recorded and reused when the remote access service is restarted. The Windows 2000 Routing and Remote Access service now releases all DHCP allocated IP addresses using DHCPRELEASE messages each time the service is stopped.

If the Routing and Remote Access service initially starts using DHCP-allocated addresses and the DHCP server becomes unavailable, then an IP address cannot be allocated to additional TCP/IP-based remote access clients.

If a DHCP server is not available when the Routing and Remote Access service is started, then the DHCP client returns 10 addresses in the range 169.254.0.1 to 169.254.255.254 to allocate to remote access clients. The address range 169.254.0.0/16 is used for Automatic Private IP Addressing (APIPA). APIPA addresses for point-to-LAN remote access connectivity work only if the network to which the Routing and Remote Access service computer is attached is also using APIPA addresses. If the local network is not using APIPA addresses, remote access clients are only able to obtain point-to-point remote access connectivity.

If a DHCP server does become available, the next time IP addresses are needed by the Routing and Remote Access service, DHCP-obtained addresses are then allocated to remote access clients that connect after the DHCP addresses were obtained.

The remote access server uses a specific LAN interface to obtain DHCP-allocated IP addresses for remote access clients. You can select which LAN interface to use from the IP tab on the properties of a server in the Routing and Remote Access snap-in.