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I have a dhcp (and dns) server running on a centos/linux pc, which is the only dhcp server on my network. I have two wireless routers - a Netgear DG834G, and a Netgear DGND3700. The DGND3700 is also the ADSL Router so it is specified as the gateway in the dhcpd.conf. The DG384G is being used as just a wireless access point.

The problem is that devices connected to the DGND3700 (ADSL router) can't get an IP, while Wired devices and devices connected to the DG384G (2nd Access Point) can. What I see in the logs in the centos pc is that clients send a DHCPDISCOVER and the server responds with a DHCPOFFER, and this keeps repeating. I don't see any DHCPREQUEST messages.

Is there something I have to configure somewhere to allow dhcp requests through the router?

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What's the client see - do the offers make it back to the client? Also - how's the network layout look as far as what's routing and what's on what subnet? –  Shane Madden Aug 3 '11 at 17:31
    
Its very strange. A couple of days ago, in a very short period of time all devices started to successfully get IPs. No changes to the setup whatsover. I guess something to do with leases from the router still remaining even after turning DHCP off - if that's possible? I don't have any other explanation! –  Musaul Aug 9 '11 at 0:09

1 Answer 1

So, just to just re-iterate. You've got DSL going into the 3700. That plugs into a switch (I'm assuming) to which the 384g, centos, and other wired computers are plugged into? You've then got the 384g and 3700 as wireless. Is the 384g's wireless bridged with the ethernet connecting to the 3700? Or is it acting as a full-blown router (You don't need it to btw).

Next, are there multiple subnets in play here? I'm assuming not. The next question is, are there any firewalls on either the client or the server which may be blocking tcp/udp (DHCP can use either/both) ports 68/69? 68 is the DHCP client port and 69 is the DHCP server port. I'm assuming the centos isn't blocking anything because it sees the dhcp discover. But is the client seeing the OFFER and sending a REQUEST?

Also, is DHCP turned OFF on the 3700 (And 384g assuming it's acting as a bridge)? If not, what could be happening is both the 3700 and the centos are sending out an offer, but the client only accepts the one from the 3700.

Also, unless there's something really fancy you're trying to do, it might be easier in a home network to just let the 3700 do the DHCP.

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Yup, DSL coming into the 3700, and the 834g is bridged via ethernet. It's being used just as an access point, and has nat and dhcp disabled. There is just one subnet here. CentOS is set to allow DHCP traffic as I can see from all wired cilents, as well as wireless clients connecting through the 834g. The problem is that the clients are all phones and tablets. Not much testing I can do there. If I turn on DHCP in the 3700, they can connect to that. I'll have to try with a laptop to see what happens I guess. –  Musaul Aug 4 '11 at 11:36

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