STP

Question 1

What is the default version of STP

Answer 1

PVSTP

Cisco proprietary

Question 2

What flavors of STP are there

Answer 2

PVSTP

Rapid STP

Portfast

Question 3

How does spanning tree work

Answer 3

Switches exchange BPDUs (Bridge Protocol Data Units)

Selects Root Bridge (for the Root Switch)

All other switches select root port (that forwards towards Root Bridge)

All switches choose Designated Port (forwarding away for Root Bridge)

Question 4

How to select the Root Switch

Answer 4

The switch with the lowest Bridge ID (BPDU) is the root switch

First goes off the Priority

Then goes off the lowest MAC ID number

Question 5

How select the root port

Answer 5

Determined on all switches but root switch

Each switch has ONLY ONE root port

Sum the cost of each link to the rootport + Cost of the root port

If there is a tie - its whoever has the lowest sender’s port number

Question 6

How select designated port

Answer 6

Add up the cost of all the links

then look at lowest bridge id

Question 7

Stages in PVST

Answer 7

Blocking

Listening (15s)

Learning (15s)

Forwarding