Many routers do that. I noted it at this link. Adjust your router as you wish.
I find folk getting pretty confused over this. But there it was, in the router manual. Also, it was not a PC setting in that case.
I'm not an expert on networking, so please bear with me if the answer to this issue is obvious!
I have been operating for some time without problems with a home network based on a Billion BIPAC 7800N modem router. The devices in the network include 2 PCs - one connected by ethernet cable to the router, and the other (usually) by Wi-Fi. Until now, I have used the router's DHCP server to allocate IP addresses, but am now allocating static IP addresses to each device.
I have set the gateway's (and the DNS server's) IP address to 192.168.1.254, with Subnet mask 255.255.255.0. I have allocated the IP address 192.168.1.1 to the ethernet card of the first PC, and IP addresses 192.168.1.2 and 192.168.1.3 to the ethernet card and wireless card of the second PC (with the same subnet mask as the router).
Connecting the second PC using the ethernet connection gives no problems.
Connecting the second PC using the wireless card prevents either PC "seeing" the other, but both PCs can access the internet.
Can anyone advise what I need to do to enable the same full network connection with using the wifi card on the second PC, as I have when using the ethernet card?