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Flashcards in Week 1 Deck (20):

What is the Rapid Spanning Tree Protocol (RSTP)?

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


What is a Bridge ID?

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


what is a Root Bridge?

The focal point for all paths
- the root bridge is the switch with the lowest bridge ID


Bridge Protocol Data Unit (BPDU)

- STP config frames
- sent between neighbour switches over native VLAN


What is Port cost?

- cost of using the port
this is based on bandwidth + ID


what is path cost?

Total cost of path from switch to root bridge


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

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


How is a Root Bridge chosen?

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


How can you configure a Root bridge?

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


What is a Root Port?

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


What is a designated port?

All root bridges are designated
- a port on a switch with lowest cost path from the root bridge
- forwards traffic


What is the role of the backup port

Path to route via another port, same segment


What is the role of the alternate port?

Pth to route via another port. Different segment


What are the four port states?

- 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


Root port

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


Designated port

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


Non designated port

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


Disabled port

port that is administratively shut down



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


Bridge id is the?

Bridge priority and mac address