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Some sites fail to load one of my computers [solved]
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iceaway
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PostPosted: Sun Sep 02, 2012 4:08 pm    Post subject: Some sites fail to load one of my computers [solved] Reply with quote

I'm having a strange network related problem on one of my computers. One site that works poorly is facebook. I can load the first page, but when I try to login the browser just sits there loading, but nothing happens. The same thing happens to some other sites as well (but not all), at first I can load the site, but when I try to login it gets stuck. If I try to use another browser, the same thing happens, the first page loads, but as I try to login it just tries to load the page forever. I have tried creating a different user on the computer, but to it has the same problems. My network setup is as follows:

computer -> [wire] -> switch -> [wire] -> wireless access point -> [wireless] -> wireless router -> [wire] -> internet

I have another computer running windows 7 connected to the switch, and I'm not experiencing any problems there. I have several other computers connected directly to the wireless network, and they aren't experiencing any problems either. I have tried looking in the settings of the router and wireless access point to see if the sites could be blocked, but I haven't found anything.

Any ideas?


Last edited by iceaway on Tue Sep 04, 2012 3:29 pm; edited 1 time in total
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krinn
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PostPosted: Sun Sep 02, 2012 5:33 pm    Post subject: Reply with quote

You should check two points, your card MTU and its metric.

The MTU depend on connection type, for classic ethernet it should be 1500 (1492 for ppp) less than that you may get lost packets (and the effect a site load slowly or not at all, while some other works)

the metric is number of hop (switch/router) in your road to internet, so for you it should be set to 3 (switch, access point, wireless router), most router can detect that but some poor drivers sometimes fail to query the correct value.

You may check wiki or some other media for info correctness. I'm not sure howto solve the metric problem, but the MTU one can be set easy.

Both could be check with ifconfig output
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iceaway
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PostPosted: Sun Sep 02, 2012 6:08 pm    Post subject: Reply with quote

I've checked both the MTU and metric, and unfortunately the MTU is 1500 and metric is 3, so that is not the problem.

Code:
$ route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.0.1     0.0.0.0         UG    3      0        0 eth0
loopback        localhost       255.0.0.0       UG    0      0        0 lo
192.168.0.0     *               255.255.255.0   U     3      0        0 eth0


Code:
$ ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.104  netmask 255.255.255.0  broadcast 192.168.0.255
        ether 50:e5:49:52:b4:19  txqueuelen 1000  (Ethernet)
        RX packets 3790510  bytes 3066773731 (2.8 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2810443  bytes 876609667 (836.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
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Hu
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PostPosted: Sun Sep 02, 2012 6:40 pm    Post subject: Reply with quote

What is the MTU on a working system? MTU should be set as high as reasonably possible and then negotiated down via PMTU discovery, but if an intervening device breaks PMTU discovery, the observed behavior could occur.
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krinn
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PostPosted: Sun Sep 02, 2012 7:12 pm    Post subject: Reply with quote

2 others possible problems i could think of would be DNS (bad server and you may wait for timeout until the resolv is done properly), something you could change using google public dns to test (8.8.8.8 and 4.4.4.4 if i remember well)
and IPv6 hell (many routers still doesn't handle well ipv6 encapsulate in ipv4, some didn't even know what ipv6 is) if some of the hops fail and others work, you'll get delay as the packet are resend and resend, until a proper path (one handling ipv6) is pickup.

I don't know where as i don't use ipv6, but you have a flag in /sys certainly to disable it temp, or rebuild a kernel without ipv6 or if build as module unload it.

That's just guess, i would have put all my bets on MTU tbh :/
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Odward
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PostPosted: Sun Sep 02, 2012 7:41 pm    Post subject: Reply with quote

iceaway wrote:
...but when I try to login it gets stuck.


Are you saying this Only applies to secure logins? Can you surf all http sites fine, but only when you attempt to login to a site you get the failure?
Can you open This page but not This one?

Just wanted to ask in case you meant literally only logins were the problem.
If that's the case I would suspect the iptables rules on the problem linux box (if you have any).
Possibly a proxy / firewall configuration on your internal network (if you utilize / configure any).
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iceaway
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PostPosted: Tue Sep 04, 2012 3:22 pm    Post subject: Reply with quote

Odward wrote:
iceaway wrote:
...but when I try to login it gets stuck.


Are you saying this Only applies to secure logins? Can you surf all http sites fine, but only when you attempt to login to a site you get the failure?
Can you open This page but not This one?

Just wanted to ask in case you meant literally only logins were the problem.
If that's the case I would suspect the iptables rules on the problem linux box (if you have any).
Possibly a proxy / firewall configuration on your internal network (if you utilize / configure any).


Now this is getting weird/annoying. I tried opening both of your links, and both would at first show me the news feed on facebook (since I am already logged in). But if I closed the two tabs I just opened from your links, and try to open them again, they don't show anything. Just a blank page while they try to load.

So I tried deleting the facebook cookies in my browser, and loading the facebook front page worked immediately. When I tried to login, I managed to load the news feed once, but then everything becomes stuck again. I cannot reload the news feed or navigate to any other pages. If I delete the cookies again, I can load both of your links.

I am not using iptables or any firewally things on my network, just NAT on the router connected to the internet.
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iceaway
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PostPosted: Tue Sep 04, 2012 3:29 pm    Post subject: Reply with quote

I think I have solved it now. I was looking through the settings on my router, and discovered that the MTU was set to 1492 there. Changing it to 1500 appears to have solved the problems. I never thought about that being a setting available on the router too.... doh!
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