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What is a firewall?
In general terms, a firewall is a system that isolates a computer or group of computers from other computers. Some firewalls use hardware to do the isolation, others use software, and many use a combination of both hardware and software.
What is a router?
A router is a specific type of firewall: network equipment which connects one network to another. For example, a router may connect a home network (LAN) to the internet. In addition to acting as a firewall, a router can provide other functions such as allowing several computers to share one external internet connection.
How do I use a web server or mail server with a firewall or router?
Typically, the firewall and/or router must be configured to forward web or mail server traffic from the external IP address (i.e. the internet) to the server machine on the LAN.
Web servers typically use port 80 (HTTP), and FTP servers use port 21.
Mail servers use port 25 (SMTP), 110 (POP3), and 143 (IMAP).
To check network configuration, run the:
Since each router and firewall are different, visit the router or firewall software vendor's web site for instructions on making configuration changes.
Caution! always write down your router and PC configuration values before making any changes, so that you can restore them if you encounter problems.
How do I configure the BEFSR41 to allow a web server to run?
Note: For the most recent information see http://www.linksys.com/
The instructions below may also work:
How do I configure the Windows XP firewall?
For information on configuring the XP firewall for a mail server, see this document.
Configuration for a web server is identical except for the port numbers.
How do I find the Gateway and DNS Server IPs for a PC?
The DNS Servers should be listed under "Host Information". Write down the number that appears, then click the button next to the number, and write down the second number that appears (if there is one).
The Default Gateway should be listed under "Ethernet Adapter Information". Write down this number.
Also write down the name of the computer listed under "Host Information" as the "Host Name".
How do I set a static IP address on a PC?
Four pieces of information are actually needed to set a static IP address:
Typically, you must choose an IP address that your router supports (e.g. 192.168.1.2). Use the Default Gateway address, DNS Server address(es), and Host Name from "winipcfg".
Step 1: Configuring the IP Address
Step 2: Configuring the Gateway Address
Step 3: Configuring the DNS Servers and Host Name
How do I check that my web server can be accessed from the internet?
Run the Web Server Test.
How do I check that my mail server can be accessed from the internet?
Run the Mail Server Test.
What should I do if the Test passes, but I still cannot access my domain or subdomain, and I have a router?
Certain routers do not allow a machine 'behind' the router (i.e. on the local area network) to access itself, or to access any other machine 'behind' the router using a domain name. The reason for this is that the domain name refers to the external IP address of the router. So, any request is routed 'out' to the internet and then back 'in' through the external IP of the router (which is configured to forward requests to the server machine). The router gets confused by this. The solution is to use the internal IP of the server (or 127.0.0.1 if on the server machine) when accessing the domain. The internal IP can be found by rolling the mouse over the server program icon displayed in the system tray (lower right portion of the screen).