Dial-Up Networking causes a new “default route” to be added to the routing table once a successful session is initiated. If the local LAN contains multiple subnets, and the PC gains access to those subnets using a default route in the routing table, the new default route added by Dial-Up Networking will supercede the original.
This has the effect of allowing access to only the local subnet, because packets destined for the other subnets will be routed to the modem rather than the network card. This problem is not specific to using a modem server and will occur when using a local modem as well.
The Microsoft Knowledgebase contains the following articles concerning this issue:
The articles only mention NT and RAS, but they are equally applicable to Dial-Up Networking on other versions of Windows.
Last Updated
25th of August, 2009