2.1.f Implement and troubleshoot spanning-tree

2.1.f [ii] Switch priority, port priority, path cost, STP timers

there are four ways to identify the root switch:

dls1#sh spann

Spanning tree enabled protocol ieee
Root ID    Priority    32769
Address     0016.479e.4500
This bridge is the root 
Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
Address     0016.479e.4500
Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/1               Desg FWD 19        128.3    P2p
Fa0/7               Desg FWD 19        128.9    P2p
Fa0/8               Desg FWD 19        128.10   P2p
Fa0/9               Desg FWD 19        128.11   P2p
Fa0/10              Desg FWD 19        128.12   P2p
Fa0/11              Desg FWD 19        128.13   P2p
Fa0/12              Desg FWD 19        128.14   P2p
1.  the first entry lists the mac of the root. the second entry lists the mac of the local switch. if they are the same… bingo

2. this bridge is the root (patently obvious)

3. there is no root port on a root switch; also no alt or blk, hence all roles are designated.

4. the status line reads all fwd

here is a command i should use more often; nice and simple:

dls1 sh span root

dls2 sh span root

note root cost on root port is 0. note root cost on dls2. note timers. no root port on dls1 (naturally) but root port on dls2 is identified.