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Unnumbered connections

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Unnumbered connections

Demand-dial connections use the Point-to-Point Protocol (PPP) during the connection establishment process. For a TCP/IP-based connection, TCP/IP connection settings are negotiated. An important element of a TCP/IP-based PPP connection is the allocation of an IP address.

When a call is initiated between demand-dial routers (either servers running Routing and Remote Access or servers running Windows NT 4.0 Routing and Remote Access Service (RRAS)), the calling router requests an IP address from the answering router. Additionally, the answering router requests an IP address from the calling router. If both routers have an IP address to give each other, the logical interface on the PPP connection for each router is assigned an IP address from the other router. This is known as a numbered connection.

Windows NT 4.0 RRAS demand-dial connections require a numbered connection. If either the calling or the answering router does not have an IP address to assign to the other router, the connection establishment process fails. In order for both routers to assign IP addresses to each other, you must configure both routers for the proper IP address assignment behavior through the properties of RRAS. A common configuration problem with RRAS is that the default configuration for IP address assignment is to obtain an IP address through DHCP, and no DHCP server is available on the network. Because no IP address is allocated to the other router, the connection establishment process fails.

This configuration issue is no longer a problem with the Routing and Remote Access service for two reasons:

  1. Use of Automatic Private IP Addressing (APIPA) addresses

    In Routing and Remote Access, the default IP address assignment configuration is still to obtain an IP address from a DHCP server. However, if a DHCP server is not available, APIPA addresses in the range from 169.254.0.1 through 169.254.255.254 are used. Therefore, the default configuration does not prevent two routers from establishing a numbered connection. For more information about APIPA, see New features for TCP/IP.

  2. Support for unnumbered connections

    By default, demand-dial connections do not require a numbered connection. The calling and answering routers still request an IP address from each other during the connection establishment process. But if one of the routers rejects the request, both routers continue with the connection establishment process. The logical interface on the point-to-point connection does not have an assigned IP address. This is known as an unnumbered connection.

When you use an unnumbered connection, on the router that requests an IP address but is rejected, a warning is logged in the system event log with the following characteristics:

  • Source: RemoteAccess

  • Event ID: 20165

  • Message text: A connection has been established on port [number] using interface [name of demand-dial interface], but no IP address was obtained.

On the router from which an IP address is requested but is not given, a warning is logged in the system event log with the following characteristics:

  • Source: RemoteAccess

  • Event ID: 20166

  • Message text: A connection has been established on port [number] using interface [name of demand-dial interface], but the remote side got no IP address.

With unnumbered connections, servers running Routing and Remote Access can connect to other routers that do not assign an IP address during the connection establishment process. For example, some Internet service providers (ISPs) prefer to use an unnumbered connection to conserve IP addresses.

Important

  • The routing protocols provided with Routing and Remote Access cannot operate over unnumbered connections. If you use unnumbered connections, you must employ static routing. This limitation is not an issue when you are using a server running Routing and Remote Access to connect to the Internet and you configure a default static IP route, rather than run a routing protocol.