Cisco Certified Support Technician (CCST) NetworkingNetwork AccessMedium
A network administrator needs to aggregate four Gigabit Ethernet links between two Cisco switches to increase bandwidth and provide redundancy. The administrator plans to use Link Aggregation Control Protocol (LACP) to dynamically bundle these links. Which of the following is a critical requirement for a successful LACP EtherChannel configuration?
- AAll interfaces must be configured with a different speed and duplex.
- BOnly two interfaces can be bundled in a single EtherChannel.
- CAll interfaces must be assigned to different VLANs.
- DAll interfaces must be configured for the same speed and duplex mode.
Show answer & explanationAnswer & explanation
Correct answer: D. All interfaces must be configured for the same speed and duplex mode.
For LACP (or any EtherChannel) to form successfully, all member interfaces must be configured with identical parameters, including speed, duplex mode, native VLAN (if trunking), allowed VLANs (if trunking), and port mode (access or trunk). Mismatched parameters will prevent the EtherChannel from forming or cause it to operate incorrectly.
Why the other options are wrong
- A. Mismatched speed and duplex will prevent EtherChannel from forming.
- B. EtherChannel can bundle up to eight active links, providing significant bandwidth and redundancy.
- C. If the EtherChannel is configured as a trunk, all interfaces must allow the same set of VLANs and have the same native VLAN. If it's an access port, all must be in the same access VLAN.
EtherChannel Configuration Requirements
Specific settings that must be identical across all physical interfaces intended to form a logical EtherChannel bundle.
- All interfaces must have the same speed and duplex.
- All interfaces must be in the same mode (access or trunk).
- If trunking, all interfaces must have the same native VLAN and allowed VLANs.
- Can bundle 2 to 8 active links.
Memory trick: All channels must match for a perfect bundle.