port authority...

root port - every switch in the diameter has a root port; the port with the least cost path to the root switch

designated port - every switch in the diameter has at least one designated port; it is a port on a LAN segment (non-root port) with the least cost path to the root switch

blocking port - a port which is neither root port nor designated port

alternate port - candidate root ports although currently blocking but close to the root switch and identified by uplinkfast as suitable

forwarding port - just that, forwarding; no other stp activity expected

you're out of your tree...

a disabled port does not participate in spanning tree; it is either administratively down, or faulty... it does not block,  it is down

a blocked port is participating in spanning tree; it blocks, yet receives bpdu's

a port moves to the listening state when determined it has the potential to forward; it is transitioning.  it is not
   sending or receiving frames, and like blocking it is receiving bpdu's but it is not sending bpdu's; it is
   transitioning to the learning state

a port transitions from listening to learning before it gets to forwarding.  in the learning state the port is now
   adding mac's to it's table. it is one step closer to forwarding.  if it loses its potential, it will revert to blocking.

forwarding... the port has made it to the show after the requisite delays in the tranistory states.  it is adding mac addresses to its table, it is sending and receiving frames and bpdu's... it is in the big's...

spanning tree, i do love thee...

spanning-tree never tires me...

rstp (802.1w) introduced new port roles; among them, discarding.  discarding replaces the
traditional roles of disabled, blocking and listening, leaving only discarding, learning
and forwarding.  discarding is in the active topology as a replacement during the
listening phase of spanning tree but still does not populate mac addresses, just as
listening doesn't in STP. so although discarding has replaced listening, discarding during
the listening phase is considered part of the active topology. this is kind of a silly point because ultimately the role is called discarding yet part of the active topology.  go fish. i guess it's actively discarding...

again, rstp only defines a discarding state from disabled through listening.

alternate and blocked ports in rstp:
An alternate port receives more useful BPDUs from another bridge and is a port blocked.

A backup port receives more useful BPDUs from the same bridge it is on and is a port
blocked.

a port blocked here is important, as opposed to a blocked port.  there are no blocked ports in rstp.

i didn't make this shit up...

spanning tree very pretty...

STP summary

1.  all bridge (switch ports) stabilize at forwarding or blocking.  Forwarding ports are considered part of the spanning tree.

2.  one switch is elected root, and its ports will all move to forwarding state.

3.  each switch receives hellos from the root, directly or through another switch. The port that receives the least cost BPDU is placed in forwarding and becomes that switch’s root port

4.  for each segment one switch forwards the BPDU with the lowest cost.  That switch becomes that segment’s designated bridge.

5.  the other interfaces are placed in blocking

6.  the root sends BPDU’s every 2 seconds. This time interval can be modified and will be noted in the BPDU.

7.  if max-age elapses (20 seconds, default) and no BPDU, panic ensues and the spanning tree changes.

8.  forward delay (default 15 seconds) is the time it takes for a port to transition through the dumbass states to forwarding. (listening, 15 seconds, learning 15 seconds)

9.  when a switch goes into listening, it sends a TCN BPDU (topology change notification) through the new path to the root. Other switches will refresh their tables with the new entry.

10. spanning tree creates these delays to prevent transitional loops because…

spanning tree, very pretty and the bpdu’s are sweet,

but the root of the poor spanning, is impossible to eat…

spanning-tree song...

spanning-tree very pretty and the bpdu's are sweet,
but the root of the poor spanning, is impossible to eat,

Michael the network cat likes that song... reow
 

STP elects a root bridge (switch) and puts all root bridge interfaces into forwarding state

Each non root bridge (switch) determines which of its ports has the least administrative cost (best) to the root bridge and STP makes that port that switch’s root port.

The switch with the lowest (best) cost  to the root is put in forwarding state.

The lowest cost switch on each segment is the designated bridge (switch) and the interface on that switch is called the designated port.

            The root bridge’s (switch) ports are always in forwarding state and the root switch (bridge) is always the designated bridge on all connected segments.

            The non root bridge root port is always forwarding. This port receives the lowest cost BPDU from the root.

            Each LAN’s designated port is always forwarding and the bridge forwarding the lowest cost BPDU is the segment’s designated bridge (switch)

             All other ports are blocking. No forwarding frames, no receiving frames.

         At first each switch claims to be root by sending BPDU’s that contain:

                 The root bridge ID- a combination switch priority and MAC address, lower number, higher priority

             The cost to reach the root- again the lower, the better

             And it’s own bridge ID

can't we just call a root bridge a root switch instead...

Stinky Toilet Paper...

this is gonna hurt you more than me...
spanning-tree port states... arrrrrrrrrrrrrrgh

after initializing, a switchport always enters the blocking state

blocking:
the port dumps the frames received
dumps frames switched for forwarding from another switch
doesn't learn shit
receives bpdu's

listening:

the port dumps the frames received
dumps frames switched for forwarding from another switch
doesn't learn shit
receives bpdu's

learning:
the port dumps the frames received
dumps frames switched for forwarding from another switch
finally gets off its dead ass and learns addresses
receives bpdu's

forwarding:
receives and forwards frames
forwards frames switched from another port
learns addresses
receives bpdu's

disabled:
doesn't do shit

why? how? wtf...

why hasn't cisco fabricated rj-45 to usb console cables?
so you can go out and spend 40 bucks to buy a 3rd party adapter...

when a root bridge is established, why is its priority 32769?
because of  sys-id-ext 1

how often does spanning-tree send hellos?
every 2 seconds

if you debug spanning-tree you can expect a lot of output at the console, so how do you preempt this?
by issuing the command un all before issuing the command debug spanning-tree... why?
so you can stop the madness by pressing up arrow and enter, to turn it off...

from a telnet session you issue debug spanning-tree... why isn't there any output to the screen?
you haven't issued terminal monitor from privileged-exec mode, that's why...

to accomplish convergence, what states must the ports be in?
blocking and forwarding

and how long does convergence take?
50 seconds

how do you turn off stp to get rid of this 50 second shit on a port?
in interface configuration mode use spanning-tree portfast and the the interface will move to forwarding on linkup