Our office has around 250 users and DHCP server (192.168.1.1 /24) and primary DNS server(192.168.1.2 /24) installed at office. I just configured linksys Wireless router(192.168.2.1 /24) for mobile phone users. But nowadays i realize that some PC and laptop users gets the ip address from wireless router and ip conflict/bad address shown on DHCP server so the user need to restart pc in order to get ip from DHCP server. How do i solve this issue? Thanks.
Sounds like you have one of the LAN ports on the wireless router connected to the 192.168.1.1 network. I would disable the DHCP server on the wireless router, and if you have the option to set a DHCP relay on the wifi router configure it to point at the DHCP server on the 192.168.1.1 network. If you need more IP addresses, configure the 192.168.1.1 network to use a /23 (255.255.254.0) subnet which will give you a total of 510 usable ip addresses ranging from 192.168.0.1 to 192.168.1.254.
The other option would be depending on if you needed to segment the network traffic so wireless users were not able to communicate with the desktops and other hard wired machines on the first network. If that is the case, edit your question and say a requirement is to have wireless and wired connections to not be able to communicate.
I think it would be unwise if I did not mention the fact that if you change subnets on any network, you should do this after business hours when you will affect the smallest number of people at your workplace and also so you don't end up looking like an idiot when suddenly the network stops working. I would suggest turning off any and all computers that are easily accessible in your environment and are non essential. I would provide static DHCP leases (or manually entered static ip addresses) for all servers, networked storage devices, network UPS. This will vary depending on your environment and the type of gear you have in it. Some smaller companies are fine with managing a few static IP address updates, but other environments where you have 1000 devices across several racks I would be looking into static DHCP leases for any device that needs to be reachable at some IP address. After you shut down all of the computers, make the changes to the DHCP scope and subnet mask on whatever device is handing out DHCP to your LAN. Afterwards just start with one computer. Turn the machine on, boot up into whatever OS and make sure that the first machine is getting the new subnet mask info and is being assigned a IP address within the expected range. Check both LAN gateway connectivity and your connection to the outside world via ping and/or going to google and searching for some term you know won't be cached in the browser to be sure you have full connectivity. If all is good, start bringing up machines, 5 at a time and check that they also have full LAN gateway and internet connectivity. If all is good, power up the rest of the machines, but you can probably get away with just testing a few vital machines (CEOs and VPs are not going to be happy if they come in and can't connect to the network because you didn't test to ensure their connection was working as expected).