some ethernet notes...

the beginning never ends...

key pin outs...

straight through 1-1, 2-2 and 3-3, 6-6
xover                1-3, 2-6 and 3-1, 6-2

straight is easy, crossed; odd to odd, even to even...  with auto- mdix it doesn't matter (automatic medium dependent interface crossover senses tx & rx)

switches detect duplex settings through auto-negotiation using flp (fast link pulses) without auto-negotiation, cisco switches will default to half duplex on 10/100 links, or full for 1000. hard setting the port disables auto-negotiation

for csma/cd here:

http://insearchofthecert.blogspot.com/search/label/csma%2Fcd

icnd2 notes for review, here:

http://insearchofthecert.blogspot.com/search/label/icnd2

forward/filter here:

http://insearchofthecert.blogspot.com/2011/10/forwardfilter-conundrum.html

rapid-pvst

it's stp per vlan, and faster... go figure...  yes virginia, every vlan has it's own christmas tree with a load balancing ornament on top...  tuning the priority will allow some of the members of the vlan to use one of the supported links while other members of the vlan will use the one's normally blocked by stp, instead of all using the same forwarding link...

all output guaranteed from my NOHO...  (new office home office)

sw2950_02#sh spann vlan 2

VLAN0002
  Spanning tree enabled protocol rstp
  Root ID    Priority    32770
             Address     0009.b73f.ce80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     0009.b73f.ce80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg BLK 19        128.1    P2p
Fa0/2            Desg BLK 19        128.2    P2p
Fa0/9            Desg BLK 19        128.9    P2p
Fa0/23          Desg FWD 19        128.23   P2p
Fa0/24          Desg BLK 19        128.24   P2p

a minor adjustment gives us this...

sw2950_02#config t
Enter configuration commands, one per line.  End with CNTL/Z.
sw2950_02(config)#int fa0/24
sw2950_02(config-if)#spann vlan 2 port-priority 0
sw2950_02(config-if)#end
sw2950_02#
2w0d: %SYS-5-CONFIG_I: Configured from console by console
sw2950_02#sh spann vl 2

VLAN0002
  Spanning tree enabled protocol rstp
  Root ID    Priority    4098
             Address     0009.b73f.ce80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4098   (priority 4096 sys-id-ext 2)
             Address     0009.b73f.ce80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/9            Desg FWD 19        128.9    P2p
Fa0/23          Desg FWD 19        128.23   P2p
Fa0/24          Desg FWD 19          0.24   P2p

sw2950_02#

aaaaaahhhhhhhhhhhhh...

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…