1-5 Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
Lab 5.2.9 EtherchannelLANSwitchingTroubleshooting
2/3 Fast0/1
Fa 0/12
FastEthernet
Crossover
Connection
ALSwitch
10.8.1.1/24
2900XL-Ent
4006 L3
Client
10.8.1.3/24
2/4 Fast0/2
Objective
The primary function of the spanning-tree algorithm (STA) is to cut loops cre-
ated by redundant links in bridged networks. The Spanning-Tree Protocol
(STP) operates at Layer2 of the OSI model and, by the means of bridge proto-
col data units (BPDUs) exchanged between bridges, elects the ports that will
eventually forward or block traffic. This protocol can fail in some specific cases
and troubleshooting the resulting situation can be very difficult, depending on
the design of the network. The most important part of troubleshooting is done
before the problem occurs.
For this exercise, utilize a systematic approach to troubleshootingEtherchannel
Switch network.
Scenario
This network is not part of the International Travel Agency.
As the Enterprise Network Administrator, you have a small, switched network
with all clients existing in the same VLAN. There are currently no fault tolerant
links in your network. You have several hosts communicating to each other be-
tween the distribution layer and access layer switches at 100MB full duplex.
Your network administrator feels performance would improve if a second
100MB link between the distribution layer switches and the access layer
switches were added. Your network administrator adds a new crossover cable
between DLSwitch and ALSwitch and reports that communications between
both switches has stopped, however, the rest of the network continues to oper-
ate. DLSwitch indicates the following message:
“STP loop - channel 2/3-4 is disabled in vlan 1”
You must investigate the Spanning-Tree configuration and Port-Channels to
ensure proper configuration.
2-5 Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
Lab Tasks
Build the network according to the diagram above.
Cable the lab as shown in the diagram.
Clear the DLRouter configuration using the following commands:
Router#erase start
Erasing the nvram filesystem will remove all files! Continue? [confirm]y[OK]
Erase of nvram: complete
Router#reload
Proceed with reload? [confirm]y
Clear the DLSwitch configuration using the following commands:
Console> (enable) clear config all
This command will clear all configurations in NVRAM.
This command will cause ifIndex to be reassigned on the next system startup.
Do you want to continue (y/n) [n]? y
Console> (enable) reset
This command will reset the system.
Do you want to continue (y/n) [n]? y
Clear the ALSwitch configuration and VLAN database using the following com-
mands:
ALSwitch#clear start
Erasing the nvram filesystem will remove all files! Continue? [confirm]y[OK]
Erase of nvram: complete
ALSwitch#delete vlan.dat
Delete filename [vlan.dat]?
Delete flash:vlan.dat? [confirm]y
ALSwitch#reload
Proceed with reload? [confirm]y
Load the file called Lab5-2-9-DLSwitchBrokenConfig.txt into the DLSwitch
switch. Load the file called Lab5-2-9-ALSwitchBrokenConfig.txt into the
ALSwitch switch.
Configure the client with the ip address, default gateway, and subnet mask
listed in the diagram.
Step 1
Define your problem.
Step 2
Gather the Facts.
Based on the current information you have, issue the following commands to
narrow down your possibilities. The first thing to check is your connections.
On the ALSwitch, check the interfaces.
3-5 Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
ALSwitch#show ip interface brief
Interface IP-Address OK? Method Status Protocol
VLAN1 10.8.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES unset down down
FastEthernet0/2 unassigned YES unset down down
FastEthernet0/3 unassigned YES unset down down
FastEthernet0/4 unassigned YES unset down down
FastEthernet0/5 unassigned YES unset down down
FastEthernet0/6 unassigned YES unset down down
FastEthernet0/7 unassigned YES unset down down
FastEthernet0/8 unassigned YES unset down down
FastEthernet0/9 unassigned YES unset down down
FastEthernet0/10 unassigned YES unset down down
FastEthernet0/11 unassigned YES unset down down
FastEthernet0/12 unassigned YES unset up up
(Note that both FastEthernet 0/1 and 0/2 interfaces are down.)
On the DLSwitch, check the interfaces.
DLSwitch> (enable) show port 2
Port Name Status Vlan Level Duplex Speed Type
2/1 connected 1 normal full 1000 No Connector
2/2 connected 1 normal full 1000 No Connector
2/3 errdisable 1 normal auto auto 10/100BaseTX
2/4 errdisable 1 normal auto auto 10/100BaseTX
2/5 notconnect 1 normal auto auto 10/100BaseTX
2/6 notconnect 1 normal auto auto 10/100BaseTX
2/7 notconnect 1 normal auto auto 10/100BaseTX
2/8 notconnect 1 normal auto auto 10/100BaseTX
2/9 notconnect 1 normal auto auto 10/100BaseTX
output truncated
2/34 notconnect 1 normal auto auto 10/100BaseTX
Port AuxiliaryVlan AuxVlan-Status InlinePowered PowerAllocated
Admin Oper Detected mWatt mA @51V
2/1 none none - - - - -
2/2 none none - - - - -
2/3 none none - - - - -
2/4 none none - - - - -
output truncated
Port Status Channel Admin Ch
Mode Group Id
2/1 connected auto silent 22 0
2/2 connected auto silent 22 0
2/3 errdisable on 25 802
2/4 errdisable on 25 802
2/5 notconnect auto silent 23 0
2/6 notconnect auto silent 23 0
2/7 notconnect auto silent 23 0
output truncated
Last-Time-Cleared
Tue Jun 12 2001, 20:28:19
(Note that both ports 2/3 and 2/4 are in a “errdisable” status.)
Step 3
Based on your observations of the ALSwitch, it appears as though the
ALSwitch inputs ports are down. On the DLSwitch you see that the DLSwitch is
disabling the port due to an error condition. Use the following commands to
help gather facts about the DLSwitch.
4-5 Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
Attempt to re-enable the ports on the DLSwitch.
DLSwitch> (enable) set port enable 2/3
Port 2/3 enabled.
DLSwitch> (enable) set port enable 2/4
Port 2/4 enabled.
DLSwitch> (enable) 2001 Jun 12 21:10:03 %PAGP-5-PORTTOSTP:Port 2/3 joined bridge
port 2/3-4
2001 Jun 12 21:10:07 %PAGP-5-PORTTOSTP:Port 2/4 joined bridge port 2/3-4
2001 Jun 12 21:10:44 %SPANTREE-2-CHNMISCFG: STP loop - channel 2/3-4 is disabled
in vlan 1
2001 Jun 12 21:10:44 %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/3-4
2001 Jun 12 21:10:44 %PAGP-5-PORTFROMSTP:Port 2/4 left bridge port 2/3-4
DLSwitch> (enable)
Step 4
Consider the possibilities. Use the information you have and your knowledge of
switches to isolate the problem.
Step 5
Create an Action Plan.
Step 6
Implement the Action Plan.
Step 7
Observe the Results of the Action Plan.
On the ALSwitch, check the interfaces using the “show ip interface
brief” command.
On the DLSwitch, check the interfaces using the “show port 2” command.
Annotate changes from what you saw in step 2.
Step 8
Document your work.
5-5 Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
. Semester 8 Internetwork Troubleshooting 1.0 - Lab 5.2.9 Copyright 2001, Cisco Systems, Inc.
Lab 5.2.9 Etherchannel LAN Switching Troubleshooting
2/3 Fast0/1
Fa. [confirm]y[OK]
Erase of nvram: complete
ALSwitch#delete vlan.dat
Delete filename [vlan.dat]?
Delete flash:vlan.dat? [confirm]y
ALSwitch#reload
Proceed with