how to config an router into a access point?

Answer 1

First I will agree with ColinC, then say that SOME routers will let you use them as access points. There are two ways to do this. (Heck some of them have an AP setting in the setup pages!) If yours does not you have two options

ONE: In the router you want to use as an AP, login, turn off ALL NAT functions. (You will have to set your computer up using a static/fixed ip which is in the same range as the router or you may well disconnect when you do this.) In other words you will not have DHCP for the LAN enabled (disable it) you can leave the router set to obtain a WAN (internet) address automatically or set an IP in the "other networks range" using static settings. But be sure you turn off all LAN functions!. This basically makes a router into an AP since it will not build a local network and will depend upon the first router to assign addresses within the connections.

Turn on the wireless and setup the SSID and security you want. (If the router has a "router or gateway" setting option set it to gateway it will not be used for routing at this point since the NAT has been turned off.)
Connect the cable from the existing connections (LAN output) to the WAN port (on the new router) and check to see that the router obtains a valid "local address". (You have to use a wired system to do this.)

TWO: You CAN setup another whole new network with it!
This one is a little more complex and you do need to understand routing and be sure you first router will allow it to work (most will). Setup your AP router to an entirely different network in the lan settings. (If the original network is 192.168.1.1 you want to make the "new network" something like 192.168.11.1 or even 192.168.0.1 just be sure it is different.) Be sure you use 255.255.255.0 as the subnet on both or you may well "cross networks" and create the problem that Colinc is telling you about. (you can use some other subnet settings but subnetting is a discussion all unto itself! see http://www.learntosubnet.com/ )
On the new system router set the WAN to a valid address in the old system (like 192.168.1.10 - use the same subnet as set in the first router and use the first router as the gateway address and the DNS server) Use an address that is NOT within the first routers DHCP ranges!!!!!!!
Enable the wireless SSID and security you want on the new system. Reboot the router! Log back into the "new" system and check to see that you can ping it, and the Old system. Once that works you have a "new" network and can use the second router as another AP.

Here is a step by step I just found
http://www.ezlan.net/router_AP.html

Happy computing!

Answer 2

Most routers can not be converted to access points. You need either a proper access point or a wireless range extender. If you try to use a second router, it conflicts with the first, and can seriously slow your connection or even stop the connection.

Answer 3

RTFM