Client IP Address Assignment

Updated: April 30, 2010

Applies To: Windows Server 2008, Windows Server 2008 R2

Typically, when you have slower WAN links or when you have dial-up links, you place a Dynamic Host Configuration Protocol (DHCP) server on each side of a remote site connection. Installing the DHCP service on a calling router or other server at a branch office lets branch office clients obtain IP addresses from that server.

However, a DHCP server located in one subnet can support other subnets. If no DHCP server is located at the branch office, when a client at the branch office requests an address, the calling router can forward the client’s request across the dial-up or VPN link to the DHCP server in the main office, which then leases the client an address. For this to work, ensure the following:

  • The calling router contains the DHCP Relay Agent (the DHCP Relay Agent component is added with the internal interface by default).

  • The calling router is configured with the DHCP server’s IP address.

  • The site-to-site connection is a persistent connection.

For an on-demand connection, if the DHCP Relay Agent is installed on a branch office router, this can cause the router to dial the main office router (for a non-VPN dial-up connection) or the local ISP (for a VPN connection that uses a dial-up link to the ISP) every time a DHCP packet is sent by a computer in the branch office network. Therefore, if you deploy an on-demand connection, install the DHCP service in the branch office and uninstall the DCHP Relay Agent on the calling router.