newbie question about firewalls and proxys

From: Hanne van Essen (hanne.van.essen_at_floris-automatisering.nl)
Date: 05/16/03 

Date: Fri, 16 May 2003 15:13:52 +0200

Hi,

I have a website on port 80 of a Apache web server, and a router. In the
router is a firewall. I have configured a Default Data filter in the
firewall to only let through traffic on port 80. This works partly. From
a lot of places I can't see my website, no problem. But some people are
not able to see my website. They get:

Problem Report
 The system detected an Unresolved Host Name while attempting to resolve
the
host specified in the requested URL.

Message ID
 UNRESOLVED_HOSTNAME

Problem Description
 DNS resolution failure encountered.

Possible Problem Cause
 The host entered has a mistake, or the requested Web site is
temporarily
unavailable in DNS.

Possible Solution
 Examine or correct any mistakes, or try again at a later time.

If I disable the firewall then people can see the website again, but not
immediately, usually a day after disabling the firewall. Someone told me
this has something to do with proxy servers? And that some machines will
call my website on a different port than 80. I am confused. How can I
know which port anybody will use to get to my website? How do I
configure my firewall so that it is safe, but my website is available?
Can anybody explain this??

Very grateful greetings,

Hanne van Essen. 








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