Information Technology Reference
In-Depth Information
Step 2
Set logging for spanning-tree to the most verbose (
set logging level spantree 7
). The following is the
default logging level (2) for spanning tree, which means that only critical situations will be reported.
Switch-A (enable)
show logging
Logging buffer size:
500
timestamp option:
enabled
Logging history size:
1
Logging console:
enabled
Logging server:
disabled
server facility:
LOCAL7
server severity:
warnings(4)
Facility
Default Severity
Current Session Severity
-------------
----------------------- ------------------------
...
spantree
2
2
...
0(emergencies)
1(alerts)
2(critical)
3(errors)
4(warnings)
5(notifications)
6(information) 7(debugging)
We are going to change the level for the spanning-tree to 7 (
debug
) so we can see the spanning-tree states
change on the port. This configuration change lasts only for the terminal session, and then it goes back
to normal.
Switch-A (enable)
set logging level spantree 7
System logging facility <spantree for this session set to severity 7(debugging)
Switch-A (enable)
show logging
...
Facility
Default Severity
Current Session Severity
-------------
----------------------- ------------------------
...
spantree
7
2
...
Step 3
Start with the port on the catalyst shut down.
Switch-A (enable)
set port disable 2/1
Port 2/1 disabled.
Step 4
Now we will check the time and enable the port. We want to see how long it stays in each state.
Switch-A (enable)
show time
Fri Feb 25 2000, 12:
20:17
Switch-A (enable)
set port enable 2/1
Port 2/1 enabled.
Switch-A (enable)
2000 Feb 25 12:
20:39
%PAGP-5-PORTTOSTP:Port 2/1
joined
bridge port 2/1
2000 Feb 25 12:
20:39
%SPANTREE-6-PORTBLK: port 2/1 state in vlan 1 changed to
blocking
.
2000 Feb 25 12:
20:39
%SPANTREE-6-PORTLISTEN: port 2/1 state in vlane 1 changed to
Listening
.
2000 Feb 25 12:
20:53
%SPANTREE-6-PORTLEARN: port 2/1 state in vlan 1 changed to
Learning
.
2000 Feb 25 12:
21:08
%SPANTREE-6-PORTFWD: port 2/1 state in vlan 1 changed to
forwarding
.
Notice from the previous output that it took about 22 seconds (20:17 to 20:39) for the port to begin the
spanning-tree blocking stage. This time was spent negotiating the link and doing DTP and PAgP stuff.
When we started blocking, we are in the spanning-tree realm. From blocking, it went immediately to
listening (20:39 to 20:39). From listening to learning took approximately 14 seconds (20:39 to 20:53).
From learning to forwarding took 15 seconds (20:53 to 21:08). So, the total time before the port actually
became functional for traffic was about 51 seconds (20:17 to 21:08).
