Can not access certain websites from all PCs on network?

[Colin]

I have three PCs connected by wireless LAN through a Netgear wireless ADSL
router. They all basically work but two of the PCs can not access certain
websites but the third one can. I can not see any difference in the
networking configuration, (all DHCP from the router). I have tried
disabling all firewalls but it makes no difference.

The sites I can't access include www.hotmail.co.uk, my online banking site
and microsoft messenger can't log in..... The problem is stable and
repeatable.

If I try to ping www.hotmail.co.uk I see that the address is resolved so I
don't think it's a DNS issue, but the pings timeout with no response. When
I try to open these sites in the browser, the browser just hangs for ages
and finally times out with 'cannot open this page'.

Any tips on how to fix this would be very welcome,

Colin.

 

[Chuck]

I have three PCs connected by wireless LAN through a Netgear wireless ADSL
router. They all basically work but two of the PCs can not access certain
websites but the third one can. I can not see any difference in the
networking configuration, (all DHCP from the router). I have tried
disabling all firewalls but it makes no difference.

The sites I can't access include www.hotmail.co.uk, my online banking site
and microsoft messenger can't log in..... The problem is stable and
repeatable.

If I try to ping www.hotmail.co.uk I see that the address is resolved so I
don't think it's a DNS issue, but the pings timeout with no response. When
I try to open these sites in the browser, the browser just hangs for ages
and finally times out with 'cannot open this page'.

Any tips on how to fix this would be very welcome,

Colin.

Colin,

When the report includes Hotmail, a secure site like online banking, and MSN
Messenger, it sounds like an MTU settings problem.
<http://nitecruzr.blogspot.com/2005/06/internet-connectivity-problems-caused.html>
http://nitecruzr.blogspot.com/2005/06/internet-connectivity-problems-caused.html

Please let us know if this suggestion is of any help. What you learn may help
others in the future, and that's the purpose of these forums.

 

[Colin]

Chuck,

Thanks for your reply. I will try what you suggest and report back here
with the outcome.

You answer raises more questions!

I presume that the MTU is set to some value when the operating system is
installed. But what would cause it to change over the life of the OS? It
cetainly would not have been changed by the users of the problem PCs.

Secondly, why do the inacccessible websites that I listed suggest an MTU
problem? What sets these sites aside from 'ordinary' websites in a way that
MTU issues prevent these sites working where other sites are unaffected?

Again, many thanks for your help,

Colin

 

[Chuck]

Chuck,

Thanks for your reply. I will try what you suggest and report back here
with the outcome.

You answer raises more questions!

I presume that the MTU is set to some value when the operating system is
installed. But what would cause it to change over the life of the OS? It
cetainly would not have been changed by the users of the problem PCs.

Secondly, why do the inacccessible websites that I listed suggest an MTU
problem? What sets these sites aside from 'ordinary' websites in a way that
MTU issues prevent these sites working where other sites are unaffected?

Again, many thanks for your help,

Colin

Colin,

The setting doesn't generally change. The network may change. Any one router
between you and a destination host may change, and become a problem. Read my
explanation, and any of the linked articles, for details. It's a fascinating
problem, and can, theoretically, hit anybody at any time.

The problem is that you make the MTU setting for your computer, and your setting
affects all destination hosts accessed by your computer. The appropriate
setting though can be different for any one or more hosts.

Windows Vista has a dynamic MTU / RWIN setting process, which self tunes your
computer for each destination. With Vista, the MTU setting will be a thing of
the past.