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Troubleshoot — an EtherChannel that will not bundle
Enterprise Advanced 4 devices 3 checked tasks 100 points Plan lab
Two cables between two switches, a port-channel configured on both, and the bundle is down — the ports are suspended. LACP and PAgP do not interoperate, and “on” does not talk to either. Read the channel-group lines on both ends and make the two sides agree. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
Two cables between two switches, a port-channel configured on both, and the bundle is down — the ports are suspended. LACP and PAgP do not interoperate, and “on” does not talk to either. Read the channel-group lines on both ends and make the two sides agree.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 3 goals show as passed (100 points).
Network status
Devices: 2 switchs, 2 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. SW-A starts with and EtherChannel already configured. SW-B starts with and EtherChannel already configured. PC-A is a host with 10.0.0.11/24. PC-B is a host with 10.0.0.12/24. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
SW-A’s bundle is up (both ports in Po1) (40 pts) Both ends use the same negotiation (LACP active/passive or both on) (30 pts) The PCs reach each other across the bundle (30 pts) The activity, in order
SW-A’s bundle is up (both ports in Po1) Why: EtherChannel joins links into one logical link, so spanning tree does not block the extras. Verify with: show etherchannel summary Both ends use the same negotiation (LACP active/passive or both on) Why: Reading a show command is the core skill of troubleshooting: the output is the truth, not your configuration. Verify with: show etherchannel summary The PCs reach each other across the bundle Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.0.0.12 Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Mixing “on” with “active” Common mistake: Different speed/duplex/VLAN settings on member ports Common mistake: Configuring the port-channel interface but not the members Why this matters
Two sides of an EtherChannel must agree on the protocol: LACP, PAgP or static “on”. LACP and PAgP do not interoperate, and “on” does not negotiate, so mismatched modes suspend the ports.
What you will be able to do
Read show etherchannel summary and port-channel flags
Match negotiation modes on both ends
Confirm the bundle and the traffic
The network
Catalyst 2960-24TT, PC — 4 devices in all, already cabled.
Gi0/1 Gi0/1 Gi0/2 Gi0/2 Fa0/1 Fa0 Fa0/1 Fa0 SW-A SW-B PC-A 10.0.0.11/24 PC-B 10.0.0.12/24 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
SW-A Catalyst 2960-24TT configure it SW-B Catalyst 2960-24TT configure it PC-A PC 10.0.0.11 / 255.255.255.0 PC-B PC 10.0.0.12 / 255.255.255.0
Cabling
SW-A Gi0/1 ↔ SW-B Gi0/1 SW-A Gi0/2 ↔ SW-B Gi0/2 SW-A Fa0/1 ↔ PC-A Fa0 SW-B Fa0/1 ↔ PC-B Fa0
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
SW-A interface range g0/1 - 2
channel-group 1 mode active
exit SW-B interface range g0/1 - 2
channel-group 1 mode on
exit Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 SW-A’s bundle is up (both ports in Po1) 40 On SW-A: show etherchannel summary — the port-channel has 2 bundled members. 2 Both ends use the same negotiation (LACP active/passive or both on) 30 On SW-B: show etherchannel summary output matches Po1\(SU\). 3 The PCs reach each other across the bundle 30 On PC-A: ping 10.0.0.12 must succeed.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Mixing “on” with “active”
Different speed/duplex/VLAN settings on member ports
Configuring the port-channel interface but not the members
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
SW-B interface range g0/1 - 2
no channel-group
channel-group 1 mode active
exit Where this is examined
CCNA (EtherChannel), CCNP ENCOR, CCIE EI.
This lab practises these topics in the zNetLaB certification courses:
Related labs
Where to start
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