IE shows intermittent "Page cannot be displayed" over WAN but LAN is OK


I have an application running on a Windows 2003 + IIS 6 server in the UK accessed from UK and European offices. Some users are getting intermittent "Page cannot be displayed".  This might not happen at all for half an hour of continuous use - or it might happen every other click.

- Users on the same LAN as the server never have problems.
- Users who connect over the internet using a VPN client never have problems.
- Users in remote offices connected via a private network get the problem.  The office is connected to the data-center via two routers on each end of a private line.  We have approached the provider of the private line and they say it's not their problem.

What might be causing this?  If it's the private network then how do we prove it?  Are there any configuration changes that I can make on the server to make the application more resillient?

If security is a possible cause then I'll go into more detail but it doesn't look like it to me.

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first thing to do is when it can't be reached is run tracert from the clients, to see where the hops are dropped

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jul17priAuthor Commented:
I use the Freeware Ping Plotter ( because it repeats the trace at intervals, shows a simple graph & shows total and % packets lost for each hop.  The repeat will be useful if it's intermittent.  I'll give that a try later unless you know of a better one.
jul17priAuthor Commented:
Web traffic is the only service affected by this problem - telnet, remote desktop etc are all fine.  So I don't think it's the lower network layers causing this problem.

I checked the IIS logs and found that some requests from the same session show the user domain\id and some do not.  When "Page cannot be displayed" is shown in the browser then the credentials are missing from the log.

The web site is configured for Integrated Windows Authentication.  Users are either loging on using an account local to the IIS server, or to an account in the same domain as the IIS server.  Both are affected equally.

How is the fact that a user has already logged on persisted? Could this be getting lost in the network?  It is not lost altogether because If I hit refresh enough times the page is displayed and the user ID is shown in the log.
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you can try this (doubt it will work)
use the command net config server /autodisconnect:-1 which disables autodisconnect
jul17priAuthor Commented:
This problem went away when the IIS server was moved into the same datacenter as the domain controller - they had previously been connected via the VPN.  So I guess it was a security problem after all - something was probably timing out in the authentication process.

Anyway I will give the points to Steven for having a go.

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