Lets say you have an existing wired network setup at your workstation or home somewhat like this
Adsl Modem/Router (192.168.1.1) => Switch => Multiple Pcs (192.168.1.10, 192.168.1.20 ...)
Now you want to add a wireless access point to this existing wired network so that you can connect to the internet wirelessly from your laptop, netbook or ipad (ipads are wifi only). For this you can use a wireless router from dlink for example. Now connecting the wireless router to the existing wired network is a bit tricky. So lets see how to do it.
Configure Dlink router
First connect a pc/laptop to the dlink router on its LAN port. Configure your pc to connect to the dlink admin page. Get inside the dlink router configuration page and do the following configuration ...
A. In the "LAN Setup" assign an ip to the dlink router that falls in the range of the internet router. Over here the internet router is 192.168.1.1 so the dlink router can be 192.168.1.100 for example. Nothing needs to be done in the "Internet Setup" section.
B. Disable DHCP on the dlink router.
The basic dlink wireless router has 1 wan port and 4 lan ports. The wan port connects to the internet router and the lan ports are used to connect other machines on the LAN. Connect the wireless router to the switch of the existing wired network like this
Dlink Router (LAN PORT) => Switch
DO NOT connect the dlink wan port to the switch. You might think that the switch supplies internet to the dlink router so it should connect to the wan port of dlink router. BUT NO just connect to one of the LAN ports on the router. Make sure that the WAN port of the router remains empty.
Check network nodes
Now reconfigure the pc connected in step 1 to make it connect to the adsl router as default gateway. Now you should be able to ping 192.168.1.1 which is the internet router of the wired network.
Also ping the dlink router (192.168.1.100 here) and check that it is replying properly. Also trying pinging to some other pcs connected to the SWITCH of wired network and ensure that all connectivity looks good.
Configure Wireless Settings
Now go back to the dlink router configuration page. This time it will be at 192.168.1.100
Go to the "Wireless Setup" section and setup wireless parameters like network name, password etc.
The dlink router might restart in some of the above steps. Once everything is done, the dlink router should be ready to be used as a wifi access point. Now use your wireless gadget (laptop or ipad) to connect to the wireless network and it should work fine.