Troubleshooting LACP Negotiation on vSphere Distributed Switch — Passive Mode Issue
Exhibit
~ # esxcli network vswitch dvs vmware lag list -n vds1 LAG ID Name Uplinks Mode Load Balancing 0 LAG0 vmnic0,vmnic1 passive Source and Destination IP
The administrator configured this LAG on a distributed switch and corresponding LACP settings on the physical switch. But the LAG is not coming up. What is a likely issue?
Quick Answer
The LAG mode being set to passive on both the vDS and the physical switch is the likely cause because LACP negotiation requires at least one side to actively initiate the exchange of control packets that establishes the aggregated link; if both ends are simply waiting to hear from the other, neither one ever speaks first, and the LAG never comes up regardless of how correctly everything else is configured. This is a subtle but common misconfiguration because passive mode is not wrong in isolation; a passive side is perfectly valid as long as the other end is active, since active mode is designed to prompt a response even from a passive partner. The problem only arises when both ends are passive simultaneously. This is distinct from the load balancing algorithm, which governs how traffic is distributed across the LAG's member links once it is already up, not whether the LAG negotiates successfully in the first place, and distinct from naming, since LACP identifies systems and ports through internal identifiers rather than the human-readable LAG name. It is also unrelated to uplink teaming's active/active setting, which is a separate concept describing standard NIC teaming failover, not the LACP negotiation mode itself. Whenever a LAG configured for LACP fails to come up despite seemingly correct settings on both sides, check whether both ends were left in passive mode instead of having at least one set to active.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The LAG mode is passive, but the physical switch is also configured as passive.
When both the vSphere distributed switch LAG and the physical switch are configured in passive mode, LACP negotiation fails because neither side initiates the negotiation. One side must be set to active for LACP to establish. Option A is incorrect because the load balancing policy (e.g., IP hash) is separate from LACP mode; it controls traffic distribution, not LACP negotiation. Option B is incorrect because the LAG name is not used by LACP; LACP uses system identifiers and port keys, so a name mismatch does not prevent the LAG from coming up. Option D is incorrect because active/active mode refers to the uplink teaming policy, not the LACP mode setting.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The load balancing policy should be IP hash.
Why it's wrong here
A distributed switch LAG requires the physical switch ports to be configured as an LACP port-channel; IP hash is a teaming policy for standalone uplinks, not LAG membership. IP hash is tempting because it is the recommended policy when using LACP on a vSphere Standard Switch, but here the LAG itself will not form without matching LACP on the physical side.
- ✗
The LAG name is not used by the physical switch.
Why it's wrong here
LACP matches partners by system priority and port keys, not by LAG name, so a differing name does not prevent the bundle forming. The name is tempting because it is the visible identifier in vCenter, but only mismatched LACP mode, keys or VLAN settings break negotiation.
- ✓
The LAG mode is passive, but the physical switch is also configured as passive.
Why this is correct
LACP requires at least one side to initiate negotiation by sending LACPDUs. With both the distributed switch LAG and the physical switch set to passive, neither transmits, so no aggregation forms. Configuring the vSphere side as active satisfies the requirement that one endpoint actively initiates the LAG.
- ✗
The uplinks should be in active/active mode.
Why it's wrong here
LACP requires the member uplinks to be in active or passive mode, not active/active, which is a teaming setting for standard vSwitch port groups. Active/active is tempting because it maximises throughput on non-LACP teams, but LACP negotiates aggregation itself.
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Variation 1. An administrator is configuring LACP on a VDS with two uplinks. Which configuration must match between the VDS and the physical switch?
hard- A.LACP mode (active/passive).
- B.LACP rate (slow/fast).
- C.LACP port key.
- ✓ D.All of the above.
Why D: For LACP on a VDS to work, the LACP mode (active/passive), the LACP rate (slow/fast), and the LACP port key (the LAG identifier) must all match between the VDS and the physical switch. Any mismatch prevents the LAG from forming or causes inconsistent behavior.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This VCP-DCV practice question is part of Courseiva's free VMware certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the VCP-DCV exam.