IP Address Assignment
Updated: February 13, 2009
Applies To: Windows 7, Windows Server 2008 R2
When a remote access client initiates a connection to the RRAS server, the client creates a temporary logical interface (also known as a virtual interface or a virtual network adapter) and requests that the RRAS server assign an IP address to this logical interface. Both Internet Protocol version 6 (IPv6) and Internet Protocol version 4 (IPv4) addresses are supported. For more information, see IPv6 Addressing and IPv4 Addressing.
IP address assignment can occur in one of the following ways:
The RRAS server obtains the IP address to assign to a remote client from a DHCP server on the intranet. This is the preferred method for IP address assignment. The RRAS server behaves like a DHCP client to the DHCP server and obtains 10 IP addresses at a time. As the remote access clients connect to the RRAS server, the IP addresses are assigned to the clients using Internet Protocol Control Protocol (IPCP). For more information, see RRAS and DHCP. DHCP can be used to assign both IPv6 and IPv4 addresses.
If a DHCP server cannot be contacted, then the RRAS server automatically assigns IPv4 addresses from the Automatic Private Internet Protocol Addressing (APIPA) range 126.96.36.199 through 169.254.255.254. If a DHCP server cannot be contacted for IPv6 addresses, then the IPv6 prefix assignment configured on the RRAS server is used by the client with a locally generated interface ID to create an IPv6 routable address.
The RRAS server obtains an IPv4 address from a static pool of addresses configured on the RRAS server. If you configure a static address pool, do not use IP addresses that are already assigned to computers or that are in a range that your DHCP server might assign to another computer. The pool can be ranges of addresses that are a subset of addresses from the IP network to which the server is attached or from a separate subnet. If the static IP address pool address ranges represent a different subnet, ensure that routes to the address ranges exist on the routers of your intranet so that traffic to the logical interface of a remote client is forwarded to the remote access server.
For IPv6, only the prefix is assigned. The interface ID is generated automatically by the client, which then uses IPv6 neighbor discovery to ensure uniqueness.
You can configure a static IP address for a selected client on the Dial-in tab of the user account for the remote client or in a network policy. When a remote client initiates a connection, creates a temporary logical interface, and requests that the remote access server assign an IP address to this logical interface, the remote access server assigns the IPv4 and IPv6 addresses specified in the remote client's user account. This method is best suited for a small number of remote users.