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General information on the relationship between RAS & DHCP


If configured to do so, RAS Server will obtain its IP pool from a DHCP server. The machine on which RAS Server is running, can be configured to obtain its WINS, DNS, etc. via DHCP.

RAS/DUN clients do not use DHCP to get their TCP/IP settings. They get their settings via PPP negotiations (in most cases) with the dial up server. The information you see related to DHCP (e.g. the DHCP server's IP) on the Dial Up Adapter is fake.

During the PPP negotiations, IPCP is the protocol used to retrieve IP settings. IPCP doesn't provide any mechanism for passing a subnet mask (only an IP and name servers). So the dial up client must choose its own mask. MS DUN clients will always use the default mask for an IP, based on the classful standard (see below). There is no way to override this.

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If the "Allow access to entire network" option in the TCP/IP configuration of the RAS Server service has been enabled, then RAS will act as an ARP proxy for its clients. Note, this applies only to the RAS client itself. If RAS is being used to connect LANs (this is not supported by MS), then the RAS server must be configured as a true router (look into RRAS).

Traditionally, an MS RAS Server would only pass DNS and WINS entries to DUN clients, if those entries were configured static on the RAS Server. If the RAS Server obtained its DNS and WINS from DHCP, it would not pass them to DUN clients. This behavior was apparently changed in a recent service pack, but I haven't been able to track down any documentation on this change.