Wireless--------AP----------Router---------Internet STAs 1-2 | | Wireless----------------------+ STAs 3-4All four stations should be assigned IP addresses in the same subnet. The router serves as the default gateway for all four stations, and must relay all intra-WLAN traffic out the right switch port to reach each station's MAC address. Based on your description, I think your router may not be relaying traffic for Wireless STAs #1 and #2 out the switch port that's connected to your AP.
If you are not using the DHCP server on your Router to assign dynamic IP addresses to all four stations, try that first. If that doesn't help, or you need to use static IP addresses, see if your router has a configuration option for static ARP entries. Configuring static ARP table entries on the router so that traffic for Wireless Stations #1 and #2 are mapped to the AP's router-facing MAC address might help. You can also try configuring static ARP entries on your Wireless STAs #3 and #4 -- your router or AP may not be responding to ARP requests on behalf of Wireless STAs #1 and #2, so #3 and #4 can't "find" them on the LAN. To debug this, try using the Windows 2000 arp and tracert commands to see where intra-WLAN packets are being sent and how far they get.
This was first published in May 2004