[pnrj]

The problem is clearly at the level of my home network, since it applies to every computer in the house, including two Windows XP laptops, a MacBook running OS X, a desktop dual-booting Ubuntu and Windows XP, and even my Nintendo Wii. It doesn't matter whether I connect wired or wirelessly.

Web pages load normally, though maybe slightly slower than usual. Not slow enough to be a problem.

But downloads are very erratic; usually small downloads (a few MB) can complete normally, but any larger than that, and they will complete partially, then suddenly stop downloading, going suddenly from the normal download rate (usually about 150 kbps) to a download rate of 0 kbps. A few seconds after that, they will fail completely; I suspect this just means they have timed out. There does not appear to be a fixed threshold of size between which downloads succeed and fail; nor does there appear to be a fixed point in the download at which all downloads fail. I can merely say to fairly high probability that all downloads over a few megs will suddenly fail at some point.

I tried sustained pings to various servers; they all seem to work fine, dropping at most 1 in every 100 packets. Latency appears normal.

My network is set up connecting to Comcast cable internet at 3 Mbps, through a Motorola Surfboard modem, to a Belkin wireless router (Wireless G plus MIMO model number FSD9230-4), which is then connected to each of the computers. I suspect the problem is at the router, but I have no idea what the problem would be. I suppose it could also be at a slightly higher level, e.g. my ISP.

I tried Comcast's tech support, but all of their suggestions were very trivial, like resetting the modem (obviously I tried that some time ago to no avail).

Any ideas?

[TerryNet]

Does the problem occur with a computer connected directly to the modem?

[pnrj]

When I connect a computer directly to the modem, I have a different problem entirely: no matter how long it waits or how many times it tries, the computer won't acquire an IP address.

Previously I just thought of this as sort of weird, but come to think of it they may actually be related.

[TerryNet]

You have to power cycle (unplug for at least 1/2 minute) the modem when switching devices connected to it. Did you do so?

[pnrj]

Yes, I did that. It's one of the first things I always try.

[TerryNet]

The second thing I would try is to unplug the modem longer--5 minutes, even 15 minutes.

[pnrj]

The problem seems to have been with Comcast's automatic DNS server assignment. I switched my whole network to use OpenDNS, and now everything seems to be working fine. I actually got to finally download Ocarina of Time for my Wii.

[JohnWill]

I had several problems with Comcast's DNS servers in the few years I had them as an ISP. They normally get sorted out after a week or so, in the meantime there are lots of public DNS servers you can use.