Modem Troubleshooting Q

[Stark]

Since I moved to ADSL2, I've had some very strange behaviour from my modem that I'm not sure how to trouble-shoot. I've elimated other equipment from the equation (cables, routers, computers etc).

Since changing to a proper-speed connection, my modem (a Logitech WAG200) loses authentication on certain sites. It's fine with long, high-speed transfers, and it's not no latency issues at ADSL1 rating (going to ADSL2 increasing my latency by 150ms for some reason). There is no notable interference on the line, and it never happens unless I use one of these sites, and consersely I can 100% reliably induce the behaviour by using these sites. The modem never loses line sync, just has to re-authenticate, and if I use it as a bridge and authenticate at the PC level, it never happens.

It always loses auth about 15s after it starts pulling data from youtube or common file-hosting sites (ie, megaupload etc). It's not a transfer thing (I pulled Win7 down at 1800kb/s without a problem). I'm not aware of any special characteristics these websites would have to cause the problem, and it only happens if the modem handles the authentication. It also never happens due to traffic through the wireless system, only the wired LAN.

I'm ready to accept that the WAG200 is just a piece of shit that can't really handle high speeds, but the 100% correlation to these sites is very strange to me. Can anyone suggest a possible systematic cause here? I'm just going to replace the modem, but it's an interesting problem I'd like to understand better.

[Xon]

Sounds like the modem is fucked and doesn't handle ADSL2 properly. It sounds like it is resetting the adsl2 communication link after the adsl2 protocal handler crashes.

This type of thing is actually quite common with the older firmwares for modems designed before adsl2 was common. Try updating the firmware and the problem might go away.

[Stark]

Oh, you wound me. Of course I've updated the firmware. It also isn't just happening on ADSL2 modem settings; I've dropped it back to ADSL1 (largely due to the 150ms latency hit I take on ADSL2), although the ISP is still using ADSL2 at their end.

Can you descibe how these specific kinds of transfers might crash a shit modem? I'm obviously going to replace it with something a little less personal use, but I'm interested in the correlation. I'm able to use other distributed sites, but I'm not sure how things like youtube or MU or whatever handle their network traffic. The modem holds up under 800kb/s torrents, as well, which consumer routers often have trouble with. I'm eager to add to my understanding here.

[Xon]

150ms latency hit from adsl2 is really bad, and means your modem has something really wrong. There should not be any latency hit from going from adsl1 to adsl2.

Try doing a trace route to say google.com.au and make sure it is identical on adsl1 and adsl2. If it is significantly different w.r.t to latencies (or going through entirely different cities) then bitch to your ISP and make them fix it.

On Whingepool, there used to be a lot of reports when adsl2 started to become common, a lot of modems which where 'designed' for adsl2 but where mostly an adsl1 modem started falling over randomly. My old DSL-504 had a quite disturbing update changelog when I finally upgraded from adsl1->adsl2, I used to keep the firmware upto date I didn't run into the numerious problems. The belkin router I've got now (+5 years old now) also had a large number of adsl2 fixes to make it stop crashing in it's firmware update changelog.

Youtube and MU probably have local mirrors which you are pulling from, most torrents will be pulling from international sources. My guess is, it is the lower latency which is making shit blow up by pumping data faster than the modem can process correctly. It may actually be a heating issue too.

[Stark]

Yeah, I think it's the case that the WAG200 isn't 'really' an ADSL2 chip (indeed, ADSL2+ compat (gdmt+ bis or whatever) was a firmware addition) and it's suffering for it. The heating thing isn't news to me; I once owned a Netcomm 1200 that overheated from torrents because the consumer chip it was based on was never designed for that kind of traffic. I can pull from my ISP at ludicrous speeds without a problem, though, so it's strange to me. It'll teach me to buy a cheapo modem years ago I guess.

[Xon]

With ADSL2+ as a firmware addon, you can only expect so much. It isn't so much as it was cheap, but cheap and old.

On a sidenote; I always remember whirlpool.net.au as whingepool.

[Stark]

It's hard to believe that once upon a time it was actually a good source of information.

[Edi]

This is right up my alley, since I do this sort of shit for a living.

ADSL2+ routers have a number of problems and the older the device, the greater the problems. It's probably not handling the handshake protocol too well, so if you can set that as ADSL2+ instead of any multimode or autodetect setting, that could help. Another thing to do, use the device in bridged mode. The reason for that is that the processors on those things are usually cheap crap that will fuck your connection up, down and sideways whenever you try to use it at any kind of speed.

The NAT translation changes for the packets just can't keep up with line speed, so your actual speed can be significantly below the achievable maximum that way. I've seen a connection go from 13 Mbps to 19 Mbps simply by switching from NAT to bridge for this reason.

Another problem if you're using NAT is that if you haven't configured the DNS servers of your ISP to the router, it may helpfully cause the computer to lose them at random intervals or under given conditions, which results in interesting connection problems. Bridging solves this as well. There are advantages to the router being just a dumb pipe and letting the computer talk to the server directly.

Then there's the part where you need to ask your ISP if they upgraded their hardware when they switched over to ADSL2+. If they did, chances are your old router is not playing nice with the new DSLAM hardware or software and at that point it's time to get a new one.

[Stark]

As I said, using bridged works great; but I have many devices on my network and I'm not sure they can all start the connection (although I really should look at the 360 and check). I'm obviously going to have to get a new one; it's just very amusing that everything works fine (speed, throughput, stability etc) until I watch a youtube video, where my modem will lose auth in about 15s. It never happens when I use the laptop or my phone over wireless though. Crazy Logitech.

[Edi]

If you can get it without undue hassle, I suggest the A-Link RR24AP(i+) model. Once you do a basic configuration of it, it's rock solid and it has three NAT ports and one bridging port in the basic, factory configuration.

If you don't configure them, they'll shit a brick a few weeks in, but once you do, the problem goes away and in all likelihood won't come back. My employer's customers have a massive number of these and it's so far been one of the most reliable (if not the most reliable) devices that I've had to deal with. Telewell's TW-EA501/510 v3 and up come a close second, but it's probably not even available in Australia.

Stay far away from the Zyxel P660 series and from D-Link. I've got nothing but bad experiences of those from the support perspective.

[Stark]

Oh don't worry, I have no intention of ever buying a D-Link product. I haven't worked with these products for some years though, so I'll have to indulge in some research.