Question : Problem: Clients can connect to database on VPN through wired ethernet but not through wireless

I just converted a client to a wireless network from a wired network. The router is a Linksys WRT54G wireless router. The wireless network adapters are all Netgear WPN111 USB wireless adapters. The USB adapters were selected because three of the five workstations are new (relatively) Dell Optiplex GX520 all-in-one systems with no PCI slots.

The workstations all connect to the router and internet just fine. They can connect and log into the VPN site. When they try to log into the database on the VPN, the connection fails saying the that server does not exist. However, when connected via network cable, they get into the database just fine. The database manager says that I need to open two UDP ports but doing that gives the same result. There are no firewalls running on the workstations. I have also tried it with encryption on the wireless and with no encryption.

Any suggestions?

Thanks in advance for any advice.

Dougal

Answer : Problem: Clients can connect to database on VPN through wired ethernet but not through wireless

You shouldn't need to open any ports by the way, with a VPN all ports are open, within the VPN, by default.

Problems similar to this are often caused by too low an MTU (Maximum Transmission Unit) size. Surprised you don't have similar problem with wired though if it is an issue. Perhaps it is a function of the wireless card vs the wired. However, it is easy enough to experiment with. Try reducing the MTU size in increments of 20 from the current default of 1500 down to 1300. How are you creating the software tunnel? if using a Windows PPTP client it should be 1430 or less. The following links will explain the problem and how to tweak the windows machine using DRTCP. You should also manually set the local (client end) router to match:
http://www.dslreports.com/faq/7752
http://www.chicagotech.net/vpnslow.htm