Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
SW1# show etherchannel summary Group Port-channel Protocol Ports 1 Po1(SU) LACP Gi1/0/1(P) Gi1/0/2(s)
Exhibit: Two switches are bundled with LACP, but only one physical link is forwarding traffic in the port-channel. What is the most likely reason?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
One member interface has a trunk configuration mismatch
A mismatch in Layer 2 settings is a classic reason a link is suspended or left out of the channel.
B
Distractor review
LACP requires exactly one active and one passive side only
Active-active works perfectly well with LACP.
C
Distractor review
STP blocks all but one interface inside every EtherChannel
STP treats the port-channel as a single logical interface.
D
Distractor review
EtherChannel cannot be used on trunk ports
EtherChannel is commonly used on trunk links.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is believing that Spanning Tree Protocol blocks all but one physical link inside an EtherChannel, causing only one link to forward traffic. In fact, STP treats the entire port-channel as a single logical interface and does not block individual member links. Another common misconception is that LACP requires one side to be active and the other passive; however, both sides can be active simultaneously. These misunderstandings can lead to incorrect answers that ignore the critical role of configuration mismatches, especially trunking parameters, which are the real cause of suspended links in EtherChannel.
Technical deep dive
How to think about this question
EtherChannel is a technology that aggregates multiple physical Ethernet links into a single logical link, increasing bandwidth and providing redundancy between switches. Cisco supports EtherChannel using protocols like LACP, which dynamically negotiates the aggregation by exchanging protocol packets to ensure both ends agree on the channel parameters. This bundling allows traffic to be load-balanced across the member links while presenting a single logical interface to higher layers. For an EtherChannel to form correctly, all member interfaces must have identical Layer 2 configurations, including speed, duplex, trunking mode, and allowed VLAN lists. LACP uses these parameters to verify compatibility; if any mismatch exists, LACP will suspend the problematic link from the port-channel, causing only the correctly configured links to forward traffic. This behavior prevents network loops and inconsistent forwarding states. A common exam trap is assuming that STP blocks individual member links inside an EtherChannel or that LACP requires one side to be passive. In reality, STP treats the entire port-channel as a single logical interface, so it does not block individual links. Also, LACP supports active-active negotiation on both sides. The practical impact is that a single link not forwarding usually signals a configuration mismatch, such as a trunk VLAN mismatch, rather than protocol or STP behavior.
KKey Concepts to Remember
- EtherChannel bundles multiple physical links into a single logical link to increase bandwidth and provide redundancy between switches.
- LACP (Link Aggregation Control Protocol) dynamically negotiates and manages EtherChannel member interfaces to ensure consistent configuration and link compatibility.
- All member interfaces in an EtherChannel must match in key Layer 2 parameters such as speed, duplex, trunk mode, and allowed VLANs for the channel to form correctly.
- A mismatch in trunk configuration, such as differing allowed VLAN lists or trunk modes, causes LACP to suspend the affected member interface from forwarding traffic.
- STP (Spanning Tree Protocol) treats an EtherChannel as a single logical port and does not block individual member links inside the port-channel.
- LACP supports active-active mode where both sides actively negotiate the channel, not requiring one side to be passive and the other active.
- EtherChannel can be configured on trunk ports, allowing multiple VLANs to be carried over the aggregated links without issue.
- When one physical link in an EtherChannel is not forwarding traffic, it usually indicates a configuration mismatch rather than a protocol limitation or STP blocking.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
EtherChannel bundles multiple physical links into a single logical link to increase bandwidth and provide redundancy between switches.
What is the correct answer to this question?
The correct answer is: One member interface has a trunk configuration mismatch — For an EtherChannel to form correctly, the member interfaces must match on key settings such as speed, duplex, trunking, and allowed VLAN list. A mismatch keeps one link from bundling even if LACP is enabled on both sides.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.