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For reasons that are too complicated to go into, we have a wired network device that doesn't work when there's a DHCP server. We're trying to connect it to a Wi-Fi Access Point so it can be accessed wirelessly. We can set up the WAP to only have DHCP on the wireless side so this is okay.

The problem comes when we want to add a second WAP (with the same SSID) to increase the range of the Wi-Fi network. Because it's connected via cable we can't use the DHCP server from the first WAP, since this will break the device. Someone has suggested putting a DHCP server on the second WAP and giving it a different IP range but I assume this will cause problems. Unfortunately I don't know enough about this area to explain why.

  1. What problems can having a DHCP server on each WAP (same SSID, different IP address range) cause?
  2. Is there any other way of setting this up so it will work?
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I don't get it. Is the DHCP-phobic device a wired device or a wireless device? –  Spiff May 10 '12 at 7:03
    
Wired - I've amended the question. –  parsley72 May 10 '12 at 8:39
    
Question 1 — Sounds like a bad idea to me. Different SSIDs would be less prone to odd behavior. Your best bet is configuring both CesarB's and dSoultanis answers. –  emgee May 18 '12 at 5:00
    
Why both? Seems to me that either would work. –  parsley72 May 18 '12 at 9:53
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3 Answers 3

Put the problematic device on a separate wired network. That is, connect it to a router, giving it a separate IP network, and connect that router to your normal network. Set up a normal DHCP server on the wired side of your normal network as you would normally do, and put the APs on it.

That is (pardon the poor ASCII art):

device |---| router |---| network (with DHCP server, APs, and whatever else you want)

Disable any NAT or firewall on that router so the device is accessible from the other side. It must have a different IP network to work (for instance, your normal network is 192.168.1.x and the device's network is 192.168.2.x). Obviously, disable the DHCP server on the router if it has one.

This is the cleanest solution IMO. It avoids being confusing, since each network is a single separate broadcast domain (one without a DHCP server, the other with a DHCP server). I believe the initial solution (one DHCP server on each AP) would work, but it is weird and would be prone to breaking in the future (and might have issues I did not think of); if you can do it in a simpler and more "correct" way (at the cost of an extra router), why not do it?

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You can always use devices (like a Cisco Aeronet 1200) as repeaters. Here you can see how this works and some info on configuration:

http://www.cisco.com/en/US/docs/wireless/access_point/1200/vxworks/configuration/guide/bkscgc12.html

Otherwise, if you don't want to spend that much money, you can always use any low budget repeater and just configure your main access point to server DHCP or any other services.

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For Q1: It will be okay, but it is not necessay.

For Q2: You can have 2 networks with the same SSID, IP range can be anything (for your requirements); however you have to put these networks on different channels. All adjacent BSSs should be on different non-overlapping independent channels. Out of 11 802.11 b/g/n channels only channels 1, 6, and 11 are non-overlapping.

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I still don't think having a device change IP address as you move round the SSIDs is a good idea. –  parsley72 May 18 '12 at 9:54
    
Generally does not matter as all these IPs are not valid and visible IPs to the rest of the Internet. –  Ali May 18 '12 at 10:02
    
There's no internet here, but since the wired device is streaming data over a socket to the wireless devices I think changing IP will have an effect. –  parsley72 May 19 '12 at 21:34
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