Requirements for Switch Link Aggregation Interfaces
Short answer
ACD The physical interface rates, duplex modes, and quantities of interconnected switches must be the same when using link aggregation.
Question
interfaces on the two switches? (Choose all that apply.)
Key Takeaways
Tests understanding that link aggregation requires symmetric configuration of speed, duplex, and member link count, while rejecting hardware-specific mismatches like SFP types.
This page explains the mandatory interface requirements for Ethernet Link Aggregation (Eth-Trunk), including speed, duplex mode, and member count consistency between switches.
Common mistake: Candidates often select Option E (same optical module model) because it seems physically necessary, but it is not a protocol requirement for link aggregation formation.
Expert Analysis
Link aggregation, specifically Ethernet Link Aggregation (Eth-Trunk), bundles multiple physical interfaces into a single logical link to increase bandwidth and provide redundancy. For this logical grouping to function correctly across both ends of the connection, specific parameters must be consistent on all member interfaces.
The most attractive but wrong answer often focuses on hardware specifics like optical modules (Option E) or interface IDs (Option B). While using identical SFP modules is good practice for interoperability, it is not a protocol requirement; different vendors can interoperate with compatible transceivers, and interface IDs are unique local identifiers that do not need to match across devices. Similarly, the quantity of interfaces (Option D) might seem like a trick, but in standard static or LACP-based aggregation, both sides must agree on the number of active member links to form a stable bundle; if one side has two links and the other expects three, the configuration will fail or drop traffic.
The critical requirements are speed and duplex mode. All member interfaces in an Eth-Trunk must operate at the same rate (Option A) to ensure uniform packet processing and hashing behavior. If speeds differ, the load-balancing algorithm cannot distribute frames evenly, leading to performance degradation or loop detection issues. Furthermore, duplex modes must match (Option C); mixing full-duplex and half-duplex creates collision domains and errors that break the logical link's integrity. Therefore, matching rates, duplex modes, and the agreed-upon number of member links are the non-negotiable constraints.
Exam Strategy
When analyzing link aggregation questions, immediately filter out hardware-specific options like SFP models or interface IDs unless explicitly stated as a vendor constraint. Focus on protocol-level consistency: speed, duplex, and VLAN membership. Remember that 'quantity' refers to the number of active member links in the bundle, which must be symmetrically configured on both ends to establish the logical channel.
Frequently Asked Questions
Do member interfaces in an Eth-Trunk need the same speed?
Is it required to use the same SFP optical modules on both sides?
Why must the number of physical interfaces be the same?
Community Votes
34% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 3
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Fmoura17 👍 1Answer: A, C, and D A. Same physical interface rates ✅ — All member interfaces must have the same speed (e.g., all 1Gbps). C. Same duplex mode ✅ — All member interfaces must use the same duplex mode (e.g., all full-duplex). D. Same number of physical interfaces ✅ — Both sides must have the same number of member links in the Eth-Trunk.
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amiie00 👍 1I think A,C,D and E sfp module must be same type SR-SR, LR-LR
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Creyes1495 👍 1Pag. 468
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