A Switch performs:
1. Learning
2. Forwarding
3. Filtering

Learning means when data is reached from source to destination, the destination send back an Acknowledgement to source for successfully arrival. So the destination find out the source address for the MAC address table and send the ACK only to source system, it is called Learning.

When a source “aa” send data to “bb”, and also “bb” send back ACK to source “aa” the address of both the source and destination is stored in MAC address table. When “aa” want to send more data to “bb” the address of “bb” present in MAC address table, it only read for it and simply forward it on the address of “bb”. It is called Forwarding.

When a Hub is connected to the switch and on the Hub “kk” and “mm” are connected to it. When “kk” want to send data to “mm” so the data will be blocked on the last port of switch which is connected to the Hub, and data will only be broadcasting in Hub not to switch too. It is called Filtering.

IOS (internetwork Operating system) Modes:
IOS or switch accessing modes are steps to access and work on switch. These are three and listed below.
1. user Mode
2. privilege Mode
3. configuration mode
1. user Mode:
User mode in initial stand by mode in which we can see user information. The syntax of the user mode is “switch>”

2. privilege Mode:
This is the second and middle mode, in which we can enter by commend “enable” from user mode. Here we can give commend such like copy, save, show or view the configuration of the switch. The syntax of the privilege mode is “switch#”.
3. Configuration Mode:
Configuration mode is the central mode and all the configuration is take place here. And we enter from privilege mode to configuration mode by commend “configure terminal” and the syntax is “switch(configure)#”.