Information Technology Reference
In-Depth Information
Now we have a total time of 21 seconds! It takes 20 seconds before it joins the bridge group (45:23 to
45:43). But then, because PortFast is enabled, it only takes 1 second until STP starts forwarding (instead
of 30 seconds). We saved 29 seconds by enabling PortFast. Let's see if we can reduce the delay further.
Step 7
Now we will turn off PAgP mode. We can see from the
show port channel
command that the PAgP mode
is set to auto, which means that it will channel if asked to by a neighbor speaking PAgP. You must turn
off channeling for at least a group of two ports; you cannot do it for just an individual port.
Switch-A (enable)
show port channel 2/1
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
2/1 connected auto
not channel
Switch-A (enable)
set port channel 2/1-2 off
Port(s) 2/1-2 channel mode set to off.
Step 8
Now let's shut down the port and repeat the test.
Switch-A (enable)
set port disable 2/1
Port 2/1 disabled.
Switch-A (enable)
show time
Fri Feb 25 2000, 13:
56:23
Switch-A (enable)
set port enable 2/1
Port 2/1 enabled.
Switch-A (enable)
2000 Feb 25 13:
56:32
%PAGP-5-PORTTOSTP:Port 2/1 joined bridgeport 2/1
2000 Feb 25 13:
56:32
%SPANTREE-6-PORTFWD: port 2/1 state in vlan 1 changed to
forwarding
.
Notice here that now it takes only 9 seconds to reach the forwarding state (56:23 to 56:32) instead of 21
seconds, as in the previous test. Turning PAgP from auto to off in this test saved about 12 second
s
.
Step 9
Let's turn trunking to off (instead of auto) and see how that affects the time that it takes for the port to
reach forwarding state. We will again turn the port off and then on, and record the time.
Switch-A (enable)
set trunk 2/1 off
Port(s) 2/1 trunk mode set to off.
Switch-A (enable)
set port disable 2/1
Port 2/1 disabled.
Start the test with trunking set to off (instead of auto).
Switch-A (enable)
show time
Fri Feb 25 2000, 14:
00:19
Switch-A (enable)
set port enable 2/1
Port 2/1 enabled.
Switch-A (enable)
2000 Feb 25 14:
00:22
%PAGP-5-PORTTOSTP:Port 2/1 joined bridge port 2/1
2000 Feb 25 14:
00:23
%SPANTREE-6-PORTFWD: port 2/1 state in vlan 1 change for
forwarding
.
We saved a few seconds at the beginning because it took only 4 seconds to reach the spanning-tree
forwarding state (00:19 to 00:22). We saved about 5 seconds by changing the trunking mode from auto
to off.
Step 10
(Optional). If the switch port initialization time was the problem, it should be solved by now. But if you
have to shave a few more seconds off the time, you could set the port the speed and duplex manually
instead of using autonegotiation.
Setting the speed and duplex manually on our side requires that you set the speed and duplex on the other
side as well. This is because setting the port speed and duplex disables autonegotiation on the port, and
the connecting device will not see autonegotiation parameters. The connecting device will connect only
