Horrible Problem - iMac disconnects when downloading

[TFIFF]

This is so frustrating! I've been loving my new iMac, but any time I try to download something for more than 3 or 4 minutes my internet connection will cut out. At first, I thought this was caused by my ISP cutting off my connection for trying to torrent. But, just now I tried downloading a normal file that was large and it cut out again. I see now that whenever I'm downloading for more than just a few minutes, everything will cut out for a while.

I don't think this has anything to do with my router, since other computers on this same connection are able to download just fine. What could be going on???

[DeltaMac]

Are you using wireless, or wired internet connection?
If wireless, try an ethernet cable connected to your router.
Try a download then.
Is it always the same time period (for example - 5 minutes) when the internet disconnects.

[TFIFF]

It is wired through a router. I tried using a wired connection directly from the modem, I tried switching ports on the router, I tried using a different cable, and had the same problem each time. And it FEELS like it is always the same time period when the internet disconnects, maybe not precisely, but usually the same.

I also just tested it over wifi, and had the same problem. Regular browsing/gaming/chatting or whatever, rock solid connection, and then any download that lasts more than a minute or so causes a disconnection.

[trevor]

When I see people able to download small files but not large files, the cause usually turns out to be that they have their MTU set at the default 1500, but their internet connection requires a smaller MTU, like 1492, 1450, or 1400. This most often happens with DSL connections. Do you connect over DSL? If so, what MTU does your ISP recommend?

Trevor

[TFIFF]

I use DSL, but I cannot find my recommended MTU. Is there a lower number I can use that will keep my ping reasonable? I care about my ping more than DL speed to be honest. Thanks for your suggestion, I am eager to try a number that you throw out there.

[TFIFF]

For reference, I just tried 1492 (not an official number, but a number I see that other people with my ISP have used with success) and still had the same problem.

[hayne]

A few years back, I used 'ping' to figure out what MTU value I needed to use
- see: http://hintsforums.macworld.com/showthread.php?t=62930

By the way, I no longer need to do this - presumably since my ISP has fixed things.

[trevor]

Hayne's idea seems excellent, check out the old forum thread that he links to above. That said, the most common MTU settings that I've seen other than the default 1500 are 1492, 1450, and 1400.

Trevor

[TFIFF]

Changing the MTU did seem to have an effect! I just downloaded a 1 GB file at 450k a second, which previously would have gotten me disconnected.

Unfortunately, I still get disconnected when trying to download a torrent file. It will get up to around 400 or 500k, last for a minute, and then cause the disconnect. I very rarely need to torrent anything though, so I might just live with this issue. I'm so happy I can download regularly, so I'll ride that high for a while. Is it possible that the torrenting issue is caused by an old router?

Thanks again

[trevor]

Have you considered calling your ISP's technical support and asking them what the MTU should be set at?

As for the old router you have, I guess it might be a possible cause (if it has some defect), but I don't think it's the most likely explanation.

Trevor