2. Spanning Tree Protocol

Question 1

What are the different types of SPT?

Answer 1

• 802.1D
• PVST
• PVST+
• 802.1W RSTP
• MST

Question 2

What are the 6 STP port states?

Answer 2

• Disabled
• Blocking (receive BPDU)
• Listening (send/receive BPDU)
• Learning (send/receive BPDU, adjust mactable)
• Forwarding
• Broken

Question 3

What are the 3 STP port types?

Answer 3

• Root port (1 per vlan)
• Designated port (1 per link)
• Blocking port

Question 4

What are the 2 types of BPDU?

Answer 4

• Configuration BPDU (discover the root bridge)

- Topology Change notification

Question 5

How to change a switch to long mode?

Answer 5

spanning-tree pathcost method long

Question 6

What are the long-mode costs?

Answer 6

• 2.000.000
• 200.000
• 20.000
• 2.000
• 1000
• 200
• 20
• 2

Question 7

What does Spanning-Tree do?

Answer 7

Enables switches to become aware of other switches through the advertisement en receipt of BPDUs. It creates a L2 loop free topology

Question 8

How can you recognize a root bridge?

Answer 8

All the ports are forwardering and designated

Question 9

What are the root bridge election steps?

Answer 9

• Every switch thinks it is the root bridge and sends out a config BPDU
• If a received config BPDU has a higer bridge identifier it ignores
• If a received config BPDU has a lower bridge identifier it updates its own BPDU

If priority is equal the lowest mac address counts

Question 10

Why is a bridge priority always higher?

Answer 10

The vlan is added to the priority

Question 11

What are the 5 steps for the roort port election?

Answer 11

• Interface with the lowest path cost
• Interface associated to the lowest system prio of advertising switch
• Interface associated to the lowest mac of advertising switch
• When multiple links are associated to the same switch, lowest port priority
• When multiple links are associated to the same switch, lowest port number

Question 12

What are the 2 port types on a catalyst switch?

Answer 12

• P2P

- P2P edge

Question 13

What happens when a switch discovers STP topology changes?

Answer 13

The switch that detects the change sends a Topology Change Notification BPDU towards the bridge. An upwards stream switch will ACK and forward the BPDU.

Question 14

What happens when the root bridge receives a TCN BPDU?

Answer 14

It creates a new BPDU configuration wit hthe Topology Change flag set. and floods it.

Question 15

What does a switch do when it receives a BPDU with the Topology Flag set?

Answer 15

They change their MAC timer to the forward delay timer (15 sec default). This flushes all macs of devices that did not respond within the 15 sec.
After a second BPDU the MAC timer is placed back to 300

Question 16

What are the 3 RSTP port states?

Answer 16

• Discarding
• Learning (forwards BPDU, not other traffic)
• Forwarding

Question 17

What are the 4 RSTP port roles?

Answer 17

• Root port
• Disgnated port
• Alternate port
• Shared segment

Question 18

What are the 3 802.1W port types?

Answer 18

• Edge port
• Non edge port
• P2P