Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
SW1: interface range g1/0/1-2 switchport mode trunk channel-group 5 mode active SW2: interface range g1/0/1-2 switchport mode trunk channel-group 5 mode desirable
A Layer 2 EtherChannel between two switches is not forming. Based on the exhibit, what is the most likely cause?
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
The switches are using different EtherChannel negotiation protocols.
LACP active cannot form a channel with PAgP desirable.
B
Distractor review
A Layer 2 EtherChannel cannot carry trunk links.
Layer 2 EtherChannels commonly carry trunks.
C
Distractor review
The channel-group number must be different on each switch.
The group number is locally significant and does not have to differ.
D
Distractor review
The member interfaces must be in access mode before the bundle can form.
Trunking is supported as long as settings match.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is believing that the channel-group numbers must match on both switches for EtherChannel to form. In reality, the channel-group number is locally significant and can differ between switches without affecting the bundle. Another frequent mistake is assuming that trunk links cannot be carried over Layer 2 EtherChannels or that member interfaces must be in access mode. These misconceptions lead candidates to eliminate correct answers incorrectly. The most critical trap is confusing the negotiation protocols; LACP and PAgP are incompatible, so mixing them prevents channel formation even if all other settings match.
Technical deep dive
How to think about this question
EtherChannel is a technology that bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy. Cisco switches support EtherChannel using two main negotiation protocols: Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP). PAgP is Cisco proprietary, while LACP is an IEEE standard (802.3ad). Both protocols negotiate the formation of the EtherChannel bundle by exchanging protocol-specific packets to ensure that the physical links have compatible configurations before bundling. For an EtherChannel to form successfully, both ends must use the same negotiation protocol or be configured statically (on or off). If one side uses LACP and the other uses PAgP, the negotiation packets are incompatible, preventing the channel from forming. Additionally, the physical interfaces must match in speed, duplex, VLAN membership, and trunking mode. The channel-group number is locally significant and does not need to match on both sides. Trunk links are fully supported over Layer 2 EtherChannels, and interfaces do not need to be in access mode to bundle. A common exam trap is assuming that the channel-group numbers must match on both switches or that trunking is unsupported over EtherChannel. Another frequent mistake is confusing the negotiation protocols and expecting LACP and PAgP to interoperate. In practice, mismatched protocols cause the EtherChannel to fail silently, making it critical to verify protocol consistency. Understanding these nuances helps avoid misconfigurations and ensures reliable EtherChannel deployment in Cisco networks.
KKey Concepts to Remember
- EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
- Cisco switches use two main EtherChannel negotiation protocols: PAgP (Cisco proprietary) and LACP (IEEE standard 802.3ad).
- Both ends of an EtherChannel must use the same negotiation protocol or be statically configured for the channel to form successfully.
- The channel-group number is locally significant and does not need to match on both switches for EtherChannel formation.
- Layer 2 EtherChannels fully support trunk links, and member interfaces do not need to be in access mode before bundling.
- Mismatched EtherChannel negotiation protocols, such as one side using LACP and the other PAgP, prevent the channel from forming.
- Physical interface parameters like speed, duplex, and VLAN membership must match on all member links for EtherChannel to function correctly.
- Understanding the difference between LACP and PAgP negotiation protocols is essential to avoid silent EtherChannel failures in Cisco environments.
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.
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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 Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
What is the correct answer to this question?
The correct answer is: The switches are using different EtherChannel negotiation protocols. — The two sides are using different channel negotiation protocols. One side is configured for LACP active, while the other side uses PAgP desirable. The physical settings also need to match, but the exhibit already shows a protocol mismatch that prevents the bundle from forming.
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.
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