Router disconnects from internet only when certain computer connects

[JoeNM84]

We have a Belkin N300 router connected to the internet through a cable modem(Comcast). Up until yesterday it worked fine for all the devices connected. But now whenever my brother's laptop connects(wireless) to the network it makes the router lose connection to the internet so all the devices connected lose connection, too obviously. Everything shows connected to the router, but the router releases it's DHCP whenever he connects. As soon as he turns off his wifi or manually chooses to disconnect... the internet fires right back up within a minute or so. We have no idea what is causing this. We did notice that his laptop was trying to connect with IPV6 while everything else was using IPV4, but we disabled that and it still was having the same problem on IPV4.
Here is what the router's security log says after he connects:
Aug/31/2012 19:47:32 9c:b7:0d:99:ed:70(Work-PC) get IP 192.168.2.3
Aug/31/2012 19:48:58 WAN DHCP client send DHCP Release
Aug/31/2012 19:48:58 WAN DHCP client send DHCP Discover
Aug/31/2012 19:49:03 WAN DHCP client send DHCP Discover
Aug/31/2012 19:49:14 WAN DHCP client send DHCP Discover
Aug/31/2012 19:49:14 WAN DHCP client receive DHCP Offer
Aug/31/2012 19:49:14 WAN DHCP client send DHCP Request
Aug/31/2012 19:49:14 WAN DHCP client receive DHCP Ack
Aug/31/2012 19:49:14 WAN DHCP client get IP 24.14.179.79

been getting a lot of this stuff, too, and don't know what is doing it:
Sep/1/2012 08:10:02 join multicast group 239.255.255.250
Sep/1/2012 08:10:03 join multicast group 224.0.0.253
Sep/1/2012 08:10:10 join multicast group 224.0.0.252
Sep/1/2012 08:10:10 join multicast group 224.0.1.60
Sep/1/2012 08:12:12 join multicast group 224.0.0.253
Sep/1/2012 08:12:12 join multicast group 224.0.0.252
Sep/1/2012 08:12:13 join multicast group 224.0.1.60
Sep/1/2012 08:12:19 join multicast group 239.255.255.250
Sep/1/2012 08:16:11 join multicast group 224.0.1.60
Sep/1/2012 08:16:12 join multicast group 224.0.0.253
Sep/1/2012 08:16:17 join multicast group 224.0.0.252
Sep/1/2012 08:16:19 join multicast group 239.255.255.250

He uses Comodo internet security software and their browser.
It did the same thing when loading into safemode with networking.
The laptop connects to the internet fine when he connects to my phone's wireless hotspot. I feel like this has to be some setting got changed by accident, but we can't find anything different when we compare his settings to mine.

(router edited to correct one)

 

[JoeNM84]

I think the multicast stuff may be from an Xbox hooked up to the router, at the very least it's a different device doing those. His laptop is not connected and some still showed up in the log.

 

[eibgrad]

Very odd. From a networking perspective, there's no logical relationship between the laptop connecting via wireless and the WAN deciding to drop its DHCP lease. It sounds like a bug.

FWIW, I have seen this problem several times before over the past several months, and iirc, it always seems to be a Belkin router, which only further makes me think it’s a bug in their firmware.

As a workaround, write down the DHCP acquired TCP/IP settings (WAN IP, netmask, gateway IP, DNS server(s), etc.), change the WAN IP to static, and enter it manually. It won’t work for the long run since any DHCP lease will eventually expire. In the meantime, I’d take this one up w/ Belkin.

P.S. If Belkin doesn't correct the problem, or even acknowledge it, it may be possible to install third party firmware (e.g., dd-wrt). It depends on the specific model and version. I wouldn’t normally recommend third-party firmware to the average consumer, but it may be the only other option. Just something to keep in mind.