Bouncing A Port -- Details

IT people have certain types of jargon or words that are not really defined anywhere. "Bouncing a port" or "bouncing an interface" is one such phrase. There is no where to really look up what this means. You can search Google, but the first result I get (experts exchange) is completely wrong.

"Bouncing a port" is a network term for shutting down a port and then immediately bringing it back up. If this does not mean anything to you, then read on for a more detailed definition.

What Is A Port

A network port or interface is a physical port on a switch or router that networking cables are plugged into. If you have Internet at your house, you probably have a simple little router/switch that your Internet Service Provider gave you. It probably has a few (often four) physical ports on it that you can plug an Ethernet cable into. There are ports.

All networks use switches and routers to move data around. These are the devices that move data from one computer to another. When you connect to a website, the data goes through a bunch of different routers and switches.

Why Bounce A Port

Sometimes routers and switches have problems. If a problem looks to be on a single port of a switch, then a network administrator can try to bounce the port.

Bouncing a port is preferred to reseting the whole switch or router. If the switch itself is restarted, then all the ports on the switch go down. Bringing down all the ports is bad, because everyone who uses the switch is affected.

Bouncing a single port only affects traffic that goes through that one port. All the other ports on the device do not notice any impact.

Bouncing a port is similar to restarting a computer. Sometimes a port will stop passing traffic. Bouncing the port resets the port, clearing some of the cached data. Just like restarting a buggy computer will often fix the problem that computer is seeing, bouncing a port might clear the problems that port is having.

How To Bounce A Port

Bouncing a port usually requires two commands, run one right after the other. First the port is shutdown (disabled) and then the port is un-shutdown (enabled).

On a Cisco switch bouncing a port would be:

# enable
# configure terminal
(config)# interface FastEthernet 0/1
(config-subif)# shutdown
(config-subif)# no shutdown
(config-subif)# end

Depending on the device, you can wait want a little bit before running the 'no shutdown' command to ensure that your port properly shutdown and that the port on the other end of the connection saw it go down. Both of these things need to happen for the bounce to take full effect.

Other networking devices should have similar or even identical commands to Cisco. Just disable the port and then re-enable it, and you have bounced the port.

A bounced port will be recorded in the device's logs in the same way it logs any port that goes down and then comes back up.