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alexynr
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Joined: 23 Mar 2004
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PostPosted: Wed Jan 18, 2012 7:52 pm    Post subject: Nightmare networking problem - Software? Hardware? Reply with quote

I am experiencing a very weird problem that I have had no luck in solving yet.

The basic idea is that certain http requests through a web browser never reach the intended web-server resulting in the web-server never responding or responding with a 408 error.

I'll start from the beginning stating all the facts and maybe someone can help or throw me an idea :)

I have a dual-booting Sony Vaio laptop that has been happily running gentoo for a while now, its wireless network playing perfectly at my home network and anywhere else I'd tried it.

Recently I switched jobs. Due to a shipment delay, the PC I would be using there had not arrived yet so I was using my laptop for a few days.

Soon I came across the problem described above. I was using my wired network connection (which I never use at home) so I thought maybe a buggy driver. Switched to the wireless. Sure enough same issues. Tried it a couple of times on different machines to ensure it wasn't an issue on the web-site itself but it was definately a problem with my system.

I didn't give it much thought since I was not gonna be usingthat system there long and it worked fine everywhere else.

A couple of days ago the new machine arrived at work. I set it up with gentoo. Spent a day compiling the system and sure enough I bumped into the exact same problems.

What's weirder is that the same requests that seem to hang through a web-browser work fine through wget.

To recap:

Problem is: Majority of websites work fine, CERTAIN http requests fail/timeout with a 408 error from the web server.

Same requests work fine through wget.

Verified the problem is specific to my 2 gentoo systems. Not upstream, not packet loss (SAME requests keep failing)

Problem appears on 2 completely different gentoo systems.

Problem appears only at my work network.


Any thoughts? Can there be an incompatibility between browser software (way http requests are formed/handled) and switch/router hardware? And if so ...how the hell do you debug that :)
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kimmie
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PostPosted: Wed Jan 18, 2012 8:01 pm    Post subject: Reply with quote

Try setting your MTU down, eg. ifconfig eth0 mtu 1412
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alexynr
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PostPosted: Wed Jan 18, 2012 8:06 pm    Post subject: Reply with quote

kimmie wrote:
Try setting your MTU down, eg. ifconfig eth0 mtu 1412


I can give it a shot but if it was an issue at that level, wouldn't the wget requests fail as well? (and wouldn't it be a much more common issue? right now only very few requests are failing..But they fail consistently)
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kimmie
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PostPosted: Wed Jan 18, 2012 8:24 pm    Post subject: Reply with quote

It's still worth a try; the server must have received a partial request for you to get a 408 error. A browser will typically add many more request headers than wget, so the browser request will be larger even though the URL is the same.

You can test the path MTU using tracepath. In order to debug this sort of thing down and dirty, you need to use a protocol analyser, eg. wireshark.
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derk
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Joined: 10 Mar 2003
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PostPosted: Thu Jan 19, 2012 4:01 pm    Post subject: Reply with quote

Have you checked to see if your network running through a proxy server at your employer .. if so they may be running a " guardian proxy as well restricting/preventing access to certain websites. If all is normal at other locations then something related to that or a problem with DNS exists .. have you tried setting a google nameserver address (8.8.8.8 or 8.8.4.4) in your resolv.conf.head file (may not exist but you can add it)

as a temporary measure to test if that is the problem add the line

nameserver 8.8.8.8

as the first nameserver entry in the resolv.conf file (will disappear on next boot)
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bigbangnet
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PostPosted: Tue Jan 24, 2012 5:16 pm    Post subject: Reply with quote

Since the problem is only in 1 specific place which is your workplace, its possible that your ISP might have problems with some routers (hops) somewhere along the route where you want to connect. Like kimmie mentionned, do a traceroute from your pc to the destination ip address. Logically you should have some timeouts along the way.if so contact your isp and give'em shit.
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