bobmay

To open a port on a router simply means to enable it. In the Cisco IOS one would use the comand "shutdown" to turn off a port, and "no shutdown" to turn on, or "open a port".
See below:

The shutdown command disables all functions on the specified interface. On serial interfaces, this command causes the DTR signal to be dropped. On Token Ring interfaces, this command causes the interface to be deinserted from the ring. On FDDI interfaces, this command causes the optical bypass switch, if present, to go into bypass mode.

This command also marks the interface as unavailable. To check whether an interface is disabled, use the EXEC command show interfaces. An interface that has been shut down is shown as administratively down in the display from this command.

Examples

The following example turns off Ethernet interface 0:

interface ethernet 0
shutdown


The following example turns the interface back on:

interface ethernet 0
no shutdown

Spitfire66

In simple terms a IP connection has around 65000 "ports" (different applications use different ports).

Usually a firewall or border router will block incoming traffic (by closing all ports incoming) but you may have a reason to "open" a port allowing traffic to enter your network - this can be done for either a specific IP address / IP address range or can be configured to allow any IP address access.

Even if a port is blocked (incoming), should an outward bound port be opened - incoming traffic will usually be able to enter this port (e.g. at home I have all incoming ports blocked - when I open my internet explorer, port80 is opened bidirectionally).

You can find a list of common ports & their usages here:

http://www.iana.org/assignments/port-numbers

Hope this helps

Samurai

You guys are awesome, thank you.