Curious failure with F-13

[Timothy Murphy]

My server runs under CentOS-5.5,
but I recently tried installing Fedora-13 as a second OS,
as a sort of backup.
Everything works fine under Fedora except for one thing -
I cannot get through to any site on any browser
on any machine (Linux and Windows) reaching the internet
through the server.

There is no apparent error, but the browser simply sits there
saying it is waiting for a response from the given site.

I've tried stopping shorewall (which I use) and iptables,
but that has no effect.
I've also tried changing the nameservers to opendns servers,
but that made no difference.

I installed Fedora from the Live KDE CD, if that is relevant.

Any suggestions for possible causes of this behaviour?
Or methods of analysing what is happening?

-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: [phone]
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland