Week 1

Question 1

What is the Rapid Spanning Tree Protocol (RSTP)?

Answer 1

IEEE 802.1w standard
Replacing and backwards compatible with IEEE 802.1d (STP)
RSTP prevents layer 2 loops
By determining best traffic path through the network
Links are blocked when they aren’t apart of the best path

Question 2

What is a Bridge ID?

Answer 2

It is a unique ID for each bridge
Combination- Priority # (1-64k) and base Mac address

ex 1: priority: 32768
Mac 1111.2222.4444
ex 2:priority: 32768
Mac 1111.3333.4444

Question 3

what is a Root Bridge?

Answer 3

The focal point for all paths

- the root bridge is the switch with the lowest bridge ID

Question 4

Bridge Protocol Data Unit (BPDU)

Answer 4

• STP config frames

- sent between neighbour switches over native VLAN

Question 5

What is Port cost?

Answer 5

• cost of using the port

this is based on bandwidth + ID

Question 6

what is path cost?

Answer 6

Total cost of path from switch to root bridge

Question 7

List the STP post cost for each of the following speeds:
10 mbps
100 mbps
1 gbps
10 gbps

Answer 7

Speed     -     cost
10 mbps  - 100
100 mbps  -  19
1 gbps   -   4
10 gbps  -  2

Question 8

How is a Root Bridge chosen?

Answer 8

It should either be a distribution or CORE switch
Typically configured in STP, root bridge is elected in STP, and lowest bridge ID wins.
we can lower the priority to change the bridge ID to a designated port

Question 9

How can you configure a Root bridge?

Answer 9

- you reduce the priority on the desired switch
Command:
Spanning-tree VLAN (n) priority (x)
n= native VLAN number
x= selected priority (default is 16384)

Question 10

What is a Root Port?

Answer 10

Port on a switch with the lowest cost path to Root Bridge
one per switch
frames forward through root ports

Question 11

What is a designated port?

Answer 11

All root bridges are designated

• a port on a switch with lowest cost path from the root bridge
• forwards traffic

Question 12

What is the role of the backup port

Answer 12

Path to route via another port, same segment

Question 13

What is the role of the alternate port?

Answer 13

Pth to route via another port. Different segment

Question 14

What are the four port states?

Answer 14

• Forwarding- forwards traffic
• Discarding - no traffic sent, listens
• Learning- no forwarding, learn MAC addr + builds table, part of convergence process
• Converged- all ports in final state

Question 15

Root port

Answer 15

The port on a non-Root bridge that is closer to the root bridge in terms of cost

Question 16

Designated port

Answer 16

The port on a network segment that is closest to the root bridge in terms of cost

Question 17

Non designated port

Answer 17

Port that blocks traffic in order to preserve a loop free topology

Question 18

Disabled port

Answer 18

port that is administratively shut down

Question 19

Bpdu

Answer 19

All switches exchange info to use for the subsequent configuration of the network
Each switch compares the parameters in the BPDU that it sends to neighbpur with the parameteres int the bpdu that it recieves from other neighbors
Inside the bpdu is the bridge id

Question 20

Bridge id is the?

Answer 20

Bridge priority and mac address