Technicolor TC8305C DOCSIS gateway not providing DHCP or reliable connectivity to Apple iOS devices

Question

I'm a Network Administrator, but I'm not sure how to proceed. I have a Technicolor TC8305C DOCSIS gateway, the Comcast brand. Every few months, I find some Apple devices will not properly negotiate DHCP leases via WLAN. I am at my wits end with this problem and nothing I do seems to resolve it. Two examples of such devices are an Apple iPhone 5, and an Apple iPad Air. The router's WLAN is set to 802.11 g/n, with WPA/WPA2-PSK (TKIP/AES) encryption.

Upon connecting to the wireless router, and typing in the correct password, something goes wrong with DHCP. The device defaults to the 169.254.0.0/16 autoconfiguration address. Checking the router's web GUI, I can see that it has assigned the device a class A IP address, and can see its MAC address and hostname. On the Apple device the Wi-Fi symbol is not displayed in the upper icon bar. Obviously, there has been a breakdown in the DHCP lease negotiation process, and/or there is a different sort of issue on one of the devices. I do not know how to rule out either device as being the cause of the problem.

When I set a static IP address on the Apple device, I still do not have connectivity, though the Wi-Fi symbol is displayed in the upper icon bar. I have verified the manually entered information is 100% correct. Setting a static (reserved) IP address in the router's web GUI, assigning it to the Apple device's MAC address, also has no effect.

I have tested the connection with the following methods, all of which result in a "host unreachable" result:

1. Ping from a known connected host on the network (from a PC).
2. Ping from the router's web GUI.
3. Ping from the Apple device to a known connected host on the network (to a PC).

I have tried resetting the router, the Apple devices, turning off AirDrop on the Apple devices, and doing a factory reset on the router. None of these are a solution, however doing a factory reset on the router seems to temporarily alleviate the problem about 20% of the time (it is mostly ineffectual). The only other thing I can think to do is a packet capture from my IDS/Wireshark, in an attempt to narrow down the problem.

Answer 1

Making sure you have the absolute latest firmware on the router and the latest iOS releases on the iPhone and iPad is a good place to start.

Also, disable WPA[1] (TKIP) and go to WPA2 (AES-CCMP) only. Having both ciphers enabled complicates multicasts and broadcasts, and critical protocols like ARP and DHCP use broadcasts. And I defy anyone to show me a device (besides the old Apple 802.11b-only AirPort cards from 1999-2002 and the related Lucent WaveLAN/Agere ORINOCO cards from the same years that used the same chipset) that supported TKIP but not AES. No one ever really needed WPA (TKIP), and yet it's been left on by default on zillions of routers where all it does is invite bugs that break multicast.

While you're tweaking router settings, make sure your multicast rate is set low (if you can even set it), and make sure 802.11b rates are enabled. There is no penalty for enabling B if you have no B devices around, and there is no advantage to disabling B if you DO have B devices nearby. But if disabling B on your router disables its support for 802.11b style signaling, it reduces the range of the network for all devices and possibly makes multicasts/broadcasts less reliable for devices at the fringe of the range. So the real solution to the problem of B-only devices is to get rid of all B-only devices, not to disable B support on the router.

If those changes don't clear things up, then yes, it's time for gathering logs and packet traces.