# STP election...when does it end?

Discussion in 'Cisco' started by ciscopimpenator@gmail.com, Apr 13, 2007.

1. ### Guest

They give a diagram of 3 switches that are competing for root bridge
status. My question is when does the election end exactly? The
book talks about the process of exchanging BPDU's with each switch
advertising themselves as root bridge. Then after they realize their
buddy next to them has a better a bridge ID they advertise him as the
root bridge.

So now we have all three switches realizing one of them is root
bridge. When does the election end exactly? After they receive 5
consecutive BPDU's stating that SW1(switch 1) is root bridge? Are
their timers? It never mentions exactly how it ends. It just says
SW1 wins!!! How did they decide SW1 wins?

, Apr 13, 2007

2. ### Guest

I kept reading and found the answer. The ports are in a listening
state by a default time of 15 seconds. For this amount of time they
listen for BPDU's and forward them. Is this correct? By the time
they transition to learning they should know who the root bridge is.

, Apr 13, 2007

3. ### saintjmfGuest

On Apr 12, 11:39 pm, ""
<> wrote:
> I kept reading and found the answer. The ports are in a listening
> state by a default time of 15 seconds. For this amount of time they
> listen for BPDU's and forward them. Is this correct? By the time
> they transition to learning they should know who the root bridge is.

Yes that is correct.
Listening and learning I believe.

There is also some setting cant remember right now but it can be set
to adjust this by putting in the possible switch traversals into the
equation.

saintjmf, Apr 13, 2007
4. ### David RosaGuest

On Apr 13, 3:58 am, ""
<> wrote:
>
> They give a diagram of 3 switches that are competing for root bridge
> status. My question is when does the election end exactly? The
> book talks about the process of exchanging BPDU's with each switch
> advertising themselves as root bridge. Then after they realize their
> buddy next to them has a better a bridge ID they advertise him as the
> root bridge.
>
> So now we have all three switches realizing one of them is root
> bridge. When does the election end exactly? After they receive 5
> consecutive BPDU's stating that SW1(switch 1) is root bridge? Are
> their timers? It never mentions exactly how it ends. It just says
> SW1 wins!!! How did they decide SW1 wins?

When a switch learn a BPDU with a root bridge and a priority more low
that it stop sending BPDU's and only look new BPDU's.

David Rosa, Apr 15, 2007