Throttled download speeds on new router with Comcast (ipv6 vs ipv4)

Solution 1:

This is actually an issue with Comcast on certain Linksys or Cisco routers. Comcast's network is ill-configured and marks all the packets as low priority. More information can be found at Comcast help forums.

The easy solution is to disable WMM. In my router this was in 'Media Prioritization', 'Settings'. With this option disabled I am able to get full download speeds on IPv4 on laptop.

However disabling WMM makes it impossible for some devices to connect in Wireless N, so this is not optimal solution.

I am just going to return the router and get one that is not Linksys or Cisco.

EDIT The same problem exists with a Netgear R6250 router. I had to disable WMM and also select "Enable QoS" (after removing all the priority rules) in settings for the same fix.

With this router I am able to connect all the clients, with laptop getting 150 Mb/s link speed and 100+ Mbs download speeds on ipv4 and ipv6, and Nexus 7 falling back to Wireless G (I think) with 54 Mb/s link speed.