Some sites on some machines not loading

First, this is not a problem with the client machines so please don't go there.  The environment is a MS Server 2003 Network behind a FortiNet router/firewall appliance.  Client machines are mostly laptops.  When the some (not all) laptops are connected to the company network some websites will not load in *any* browser (IE, Mozilla, or Firefox).  MS related sites will not load (Hotmail, MSN, Windows updates).  There is no error it will try to load the page for several minutes then just stops trying.  The affected machines have nothing in common, they are different models and different ages.  However, not all machines are affected.  I've taken the IP from a machine that works and put in on a machine that does not, but that did not resolve.  I've wiped and reloaded a machine, but that did not resolve.  It has affected machines taken out of the box from the manufacturer.  And they can still access some pages, for instance, Google pages always load perfectly.

Now, when these laptop (all owned by the company) are taken home by the employees and connected to the employees home networks they can access all pages perfectely.
 
ritchdavisAsked:
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ee_ai_constructCommented:
PAQ / Refund
ee ai construct, community support moderator
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Jay_Jay70Commented:
temporarily wipe your security off the firewall and see if pages start to work
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jcdesign4uCommented:
Maybe there's a group policy active which causes this problem.
Could be a proxy setting, or restricted sites.
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ritchdavisAuthor Commented:
Thanks for the comments.

Firewall and webfiltering have been turned off, the systems restarted, but the same systems still have trouble.

No proxy server is being used and the troubled machines are not set for proxy.  Group policies all seem correct.  The sites are are not restricted on the troubled machines.
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ritchdavisAuthor Commented:
It looks like we are going to try replacing the router.
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jcdesign4uCommented:
Maybe resetting the router also helps?
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ritchdavisAuthor Commented:
Here's the solution to this problem... We didn't have to replace the router after all.  The reason some machines on the internal network could not access some websites is because the MTU on the router was set too high for the ADSL connection to the internet.

I hope this will be useful to someone else.
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ritchdavisAuthor Commented:
We dropped the MTU to 1452 and it now works perfectly.
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Jay_Jay70Commented:
well done and thanks for posting
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