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Certain websites not opening - might be squid problem

Posted on 2010-11-17
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Last Modified: 2012-05-10
Hi

Since monday we have a problem at one of our three campuses where certina websites are extremely slow to open and others wont open at all (time - outs).

The only common denominator in these sites I can see is that they all require logins yet other sites like gmail(or any google login sites) , twitter, forums and expert exhange have no problem.

some of the sites that wont open:
www.facebook.com (marketing purposes ...really)
http://students.autodesk.com
http://autodesk.starttest.com


We are running a clarkconnect server (ClearOS - Centos) with a squid proxy non transparent.
All three campuses have the same setup and the other two are working fine.

Thank you

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Question by:QuintusSmit
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by:Kent W
ID: 34161705
The login may just be a coincidence.  This sure sounds like an MTU based problem to me.
What MTU is this node using, and what is the actual connection type?
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by:QuintusSmit
ID: 34161857
The connection is a dsl line (1024mb line). How do I check the MTU size?
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Kent W earned 250 total points
ID: 34162627
Ahhh...as is the most likely culprits. :)  Happens a lot on DSL.
Check your router, it will probably auto-negotiate MTU to something like 1490 (most Broadband / Lan use 1500).
The problem is, your client computers are using 1500 by default, so you will need to download a program like
DRTCP (free), and match the MTU on your router on the NIC, lan or wireless interface, of your client computers.
It's annoying, but quite common on DSL lines.  Just google DRTCP, it will be available at dslreports.com.
Run the exe, select the NIC(s) you need to change, select the MAXMTU window and change 1500 to match your router...if you can't find that value, try 1490.  Save, reboot, and wham, all the sudden pages start loading.
99.9% sure this will fix your problem.  If 1490 doesn't work, or work well, lower it by 10s down to a max of about 1460.  If your MTU doesn't become happy, it's something else.
But I bet my first wife's alimony this will fix you up.  
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by:QuintusSmit
ID: 34186067
@mugojava: so i was wondering..should i give you my bank details for those alimony payments or would you prefer to send cheques? :)

At the moment that solution is not working however, I would still like to test it more extensively on some other pc's - I have been very busy but will keep you updated.
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by:Kent W
ID: 34193077
Really?  That surprises me, when the old "DSL" +"some pages slow or not loading" issue comes up, especially if some sites are just fine, with no rhyme or reason, I have yet to NOT have it be an MTU issue. Make sure you have the actual adapter you are connecting to the net with (Ie, don't select the LAN nic if you connect to the router with a wireless adapter, and vice-verca) when setting the MTU value.
On a hilarious note, one of the sites that usually had problems with askewed MTU was "marthastewart.com" :O)  Now that's funny, I don't care who ya are!"
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by:QuintusSmit
ID: 34226359
@mugojava

Thank you for your help and input. I'm going to award you the points for that. The problem it turns out was something with the squid proxy. Don't really have an answer but as soon as we narrowed it down to that we reinstalled squid and everything was fine.
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by:Kent W
ID: 34227853
Well, I do appreciate that, and if this helps, I've also had a similar problem with Squid on DSL...you probably looked already on this, but just in case, check out Path MTU Discovery (PMTUD) and things it can hose.  Other culprits... ECN and TCP Window Scaling can also cause Squid to hang during certain conditions.
Sure hope that helps some way. :)
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