Information Technology Reference
In-Depth Information
The trunk mode was set to desirable. The result was that trunking mode was negotiated with the neighbor
switch, and both decided on ISL (
n-isl
). The current status now is
trunking
. The following shows what
happened on Switch B because of the command issued on Switch A.
Switch-B (enable)
2000 Jan 17 19:09:52 %DTP-5-TRUNKPORTON:Port 2/1 has become isl trunk
2000 Jan 17 19:09:52 %DTP-5-TRUNKPORTON:Port 2/2 has become isl trunk
2000 Jan 17 19:09:52 %PAGP-5-PORTFROMSTP:Port 2/1 left bridge port 2/1-4
2000 Jan 17 19:09:52 %DTP-5-TRUNKPORTON:Port 2/3 has become isl trunk
2000 Jan 17 19:09:52 %PAGP-5-PORTFROMSTP:Port 2/2 left bridge port 2/1-4
2000 Jan 17 19:09:53 %DTP-5-TRUNKPORTON:Port 2/4 has become isl trunk
2000 Jan 17 19:09:53 %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/1-4
2000 Jan 17 19:09:53 %PAGP-5-PORTFROMSTP:Port 2/4 left bridge port 2/1-4
2000 Jan 17 19:09:55 %PAGP-5-PORTTOSTP:Port 2/1 joined bridge port 2/1-4
2000 Jan 17 19:09:55 %PAGP-5-PORTTOSTP:Port 2/2 joined bridge port 2/1-4
2000 Jan 17 19:09:55 %PAGP-5-PORTTOSTP:Port 2/3 joined bridge port 2/1-4
2000 Jan 17 19:09:55 %PAGP-5-PORTTOSTP:Port 2/4 joined bridge port 2/1-4
Switch-B (enable)
show trunk 2
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
2/1
auto
n-isl
trunking
1
2/2
auto
n-isl
trunking
1
2/3
auto
n-isl
trunking
1
auto
n-isl
trunking
2/4
1
Notice that all four ports (2/1-4) became trunking even though we specifically change only one port (2/1)
to desirable. This is an example of how changing one port in the channel affects all the ports.
Troubleshooting EtherChannel
The challenges for EtherChannel can be divided into two main areas: troubleshooting during the
configuration phase, and troubleshooting during the execution phase. Configuration errors usually occur
because of mismatched parameters on the ports involved (different speeds, different duplex, different
spanning-tree port values, and so on). But you can also generate errors during the configuration by
setting the channel on one side to on and waiting too long before configuring the channel on the other
side. This causes spanning tree loops, which generate an error and shut down the port.
When an error is encountered while configuring EtherChannel, be sure to check the status of the ports
after correcting the EtherChannel error situation. If the port status is errdisable, the ports have been shut
down by the software, and they will not come on again until you enter the
set port enable
command.
If the port status becomes errdisable, you must specifically enable the ports using the
set
port enable
command for the ports to become active. Currently, you can correct all the
EtherChannel issues, but the ports will not come up or form a channel until they are enabled
again. Future versions of the operating system may periodically check whether errdisable
ports should be enabled.
Note
For the following tests, we will turn off trunking and EtherChannel. The following topics will be
covered:
Setting mismatched parameters
•
Waiting too long before configuring the other side
•
Correcting errdisable state
•
Showing what happens when a link breaks and is restored
•
