Speed and Duplex

By default every single port on a Cisco switch has speed set to auto and duplex set to auto. 

So these ports will auto detect everything that plugs in, such as PC, ROUTER, SEVER. These ports will auto detect that at what speed the LAN card is running, and in what mode it is transmitting data, such as half-duplex or full-duplex. But problem is that auto detect mechanism is now old. Also some times the auto detect mechanism detects incorrectly on switch port. Switch always detects the speed correctly, but there can be some problem in detecting the duplex, whether half or full duplex.

Chances of error in auto case are around 5 %.

In practical scenarios, what we do is that we hard code the speed and duplex between

Ø  Switches.

Ø  Switch and router.

Ø  Switch and server.

Ø  Switch and printer.

And let the connection between switches and PCs on auto detection of duplex and speed.

Some useful Commands

Logging Synchronous:

This command stops the interruption of status messages during command writing.

Exec-timeout: 

By default the idle timer for device is 5 minutes, means that if you don’t do anything for 5 minutes then you will be kicked off, or disconnected. It is good for security in case we forgot to disconnect our self from the console line. With this command under “line console 0” and “line vty 0 15” we can define the disconnection time as well.

No ip domain-lookup:

It turns off the domain lookup feature.

Alias of a command:

It is actually a shortcut for using a command.

3^rd # alias exec (letter of your choice) (command whose alias we want to make)

Port Security

Port security means what devices can plug into our switch port OR how many devices can plug into our switch. 

The status messages that we often see in our switches or routers about “configured from terminal” or “Line protocol is up or down” etc. they are controlled by command, 

2^nd # terminal monitor

Some useful commands about Port Security

2^nd # show port-security.

2^nd # show port-security interface fastethernet  0/1.

2^nd # sh int fa 0/1 switch-port.

2^nd # show interface description.