A firewall is a system that isolates your computer from the Internet, usually for security reasons. A firewall helps prevent unauthorized access to your computer from other people on the Internet. A firewall can be implemented using software on your computer (such as ZoneAlarm), or with an outboard hardware device such as a router.
A router (as used in the home) is a device which allows more than one computer to communicate over a single connection, such as a connection to the Internet. Routers have become more common in homes as home networks and high-speed connections, such as cable or DSL, have become more popular. Typically, cable companies and DSL service providers allocate only one Internet address to an entire household, in which there may be several computers. The router must decide which computer should receive each packet of data which comes in from the Internet.
Firewalls are usually configured to allow your computer to make requests anywhere on the Internet, and receive replies. Some programs, however, must be able to accept unsolicited data from the Internet. EchoLink is an example of such a program. When you are connected to another station using EchoLink, you and the other station take turns sending data to each other, so each station's PC must be able to receive data without having requested it.
The protocol for this type of exchange is called UDP, or User Datagram Protocol. If you are using a firewall or router to connect to the Internet, you will probably need to configure it to accept UDP information on specific ports. (A port is part of an address.)
EchoLink uses UDP ports 5198 and 5199. To use EchoLink, you must configure your router to direct all incoming data on these two ports to the PC on which EchoLink is installed. Typically, there are two ways to configure this:
EchoLink also uses TCP port 5200. Most routers will handle these requests correctly, since EchoLink always initiates them from the local computer. If you are using firewall software, however, you may need to "open up" outbound connections to this port. (EchoLink does not use TCP for incoming connections.)
Routers and firewalls are manufactured by many different companies, and each has its own peculiar set of instructions for configuration. Some newer DSL modems have routing or firewalling features built in. For details on how to configure your router or firewall, consult the documentation that came with your device, or the company's Web site.
For more information, including step-by-step solutions for several popular routers and firewalls, see the Firewall Solutions page on the EchoLink Web site.