Switch summary

[Switch and Bridge's different thing]

1. Switch can deal with frame as hardware.

2. Switch has more port than bridge.

3. Switch is faster than bridge and can connect different interface speed.

4. Switch can support  Cut-through and Store-and-forwarding ways.





[Switch's 5 features]

1. Learning : Save MAC address at table.

2. Flooding : Flooding frames the other ports except input port.

3. Forwarding : Forwarding frames to destination port.

4. Filtering : Cut the other bridges, stop flooding frames.

5. Aging : Remember MAC address during 5 minutes.





[Reason for using Spanning-tree protocol]

1. Stop looping in case that switches has more than 2 paths.

2. Prevent Switch's disaster and recover fault.





[STP's features]

Exchange BPDU(Root BID, Path Cost, Sender BID, Port ID) every 2 seconds.

★ BID : 16bit + 48bit = 32,768(default value) + MAC address

1. Root BID : Root Bridge's ID

2. Path Cost : The value of 1,000Mbps devided by 10.

3. Sender BID : Non-Root Bridge's BID

4. Port ID : Port's ID

=> Lower BPDU's value has priority.





[STP's procedures]

1. Elect one root-bridge per one network.

2. The other bridges must elect one root-port.

3. Elect one designated-port per segmentation.





[Changes of STP's status]

1. Disabled : Shutdown

2. Blocking : Status of first running or blocking. elect root-bridge and port role.

3. Listening : Waiting status after port election.

4. Learning : Learning MAC address.

5. Forwarding : Exchange frames each other.





[STP Timer]

1. Hello Time : Forward BPDU every 2 seconds.

2. Max Age : Wait BPDU upto 20 seconds.

3. Forwarding Delay : Wait upto 30 seconds.



★ RSTP can change status as soon as possible. because that switch can propose itself as root-bridge.