Information Technology Reference
In-Depth Information
Technically, the listening and learning stages should both be 15 seconds, which is how the
forward delay parameter is set for this VLAN. The learning stage probably is closer to 15
seconds than 14 seconds if we had more accurate measurements. None of the measurements
here are perfectly accurate—we are just trying to give a feel for how long things take.
Note
We know from the previous output and from the
show spantree
command that the spanning tree is active
on this port. Let us look at other things that could slow the port reaching the forwarding state. The
show
port capabilities
command shows that this port has the capability to trunk and to create an
EtherChannel. The
show trunk
command indicates that this port is in auto mode and that it is set to
negotiate the type of trunking to use (ISL or 802.1q, negotiated through Dynamic Trunking Protocol
[DTP]).
Step 5
Switch-A (enable)
show port capabilities 2/1
Model
WS-X5225R
Port
2/1
Type
10/100BaseTX
Speed auto,10,100
Duplex half,full
Trunk encap type 802.1Q,ISL
Trunk mode on,off,desirable,auto,nonegotiate
Channel 2/1-2,2/1-4
Broadcast suppression percentage(0-100)
Flow control receive-(off,on),send-(off,on)
Security yes
Membership static,dynamic
Fast start yes
Rewrite yes
Switch-A (enable)
show trunk 2/1
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
2/1
auto
negotiate
not-trunking 1
...
First, we will enable PortFast on the port. Trunking negotiation (DTP) is still in auto mode, and
EtherChannel (PAgP) is still in auto mode.
Step 6
Switch-A (enable)
set port disable 2/1
Port 2/1 disabled.
Switch-A (enable)
set spantree portfast 2/1 enable
Warning: Spantree port fast start should only be enabled on ports connected
to a single host. Connecting hubs, concentrators, switches, bridges, etc. to
a fast start port can cause temporary spanning-tree loops. Use with caution.
Spantree port 2/1 fast start enabled.
Switch-A (enable)
show time
Fri Feb 25 2000, 13:
45:23
Switch-A (enable)
set port enable 2/1
Port 2/1 enabled.
Switch-A (enable)
Switch-A (enable)
2000 Feb 25 13:
45:43
%PAGP-5-PORTTOSTP:Port 2/1 joined bridgeport 2/1
2000 Feb 25 13:
45:44
%SPANTREE-6-PORTFWD: port 2/1 state in vlan 1 change to
forwarding
.
