Jumbo Frames MTU Mismatch in vSphere Distributed Switch
An administrator has enabled jumbo frames (MTU 9000) on a vSphere Distributed Switch. Virtual machines on different hosts cannot communicate, but VMs on the same host can. The physical switches support jumbo frames. What is the most likely cause?
Quick Answer
The answer is that the physical NICs are not configured with MTU 9000. Even when a vSphere Distributed Switch and its port groups are set to jumbo frames, the physical network adapters on each ESXi host must also have their MTU raised to 9000; otherwise, the physical NICs will drop any frame larger than the standard 1500 bytes, breaking inter-host communication while leaving intra-host traffic unaffected. On the VMware Certified Professional Data Center Virtualization VCP-DCV exam, this scenario tests your understanding that jumbo frames require end-to-end consistency across the virtual switch, the physical NIC, and the physical switch—a common trap is assuming the DVS setting alone is sufficient. Remember the memory tip: “Same host works, cross-host breaks? Check the physical NIC MTU.”
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 physical NICs are not configured with MTU 9000.
Jumbo frames must be enabled on the physical NICs (vmnic) as well as the virtual switch. If the physical NICs are still set to MTU 1500, frames larger than 1500 bytes will be dropped when they reach the physical switch port, preventing inter-host communication while intra-host communication remains unaffected. Option A is incorrect because QoS configuration does not relate to MTU issues. Option B is incorrect because VMkernel adapters are used for management and vMotion traffic, not VM data traffic. Option C is incorrect because the distributed switch port group MTU is inherited from the DVS, which already has MTU 9000.
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 physical switch QoS is misconfigured.
Why it's wrong here
Incorrect. QoS configuration does not relate to MTU issues.
- ✗
The VMkernel adapters are still using default MTU.
Why it's wrong here
Incorrect. VMkernel adapters are used for management and vMotion traffic, not VM data traffic.
- ✗
The distributed switch port group MTU is set to 1500.
Why it's wrong here
Incorrect. The distributed switch port group MTU is inherited from the DVS, which already has MTU 9000.
- ✓
The physical NICs are not configured with MTU 9000.
Why this is correct
Correct. The physical NICs (vmnic) must also be set to MTU 9000 for jumbo frames to work across hosts.
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Same concept, more angles
1 more way this is tested on VCP-DCV
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A vSphere administrator notices that after adding a new ESXi host to a vSphere Distributed Switch (vDS), some VMs on existing hosts lose network connectivity intermittently. What is the most likely cause?
medium- ✓ A.The vDS MTU setting does not match the physical network MTU.
- B.The new host's physical uplink is faulty, causing broadcast storms.
- C.The vDS is configured with LACP, and the new host's links are not properly bundled.
- D.The vDS Network I/O Control settings are not evenly distributed.
Why A: When a new ESXi host is added to a vDS with a different MTU setting than the physical network, packets may be silently dropped or fragmented, causing intermittent connectivity loss for VMs on existing hosts. This is because the vDS MTU must match the physical network MTU to avoid issues. Option B is incorrect because a faulty physical uplink would affect only VMs on that specific host, not VMs on other existing hosts. Option C is incorrect because LACP misconfiguration would typically cause issues with the new host's connectivity, not intermittent connectivity for VMs on hosts already in the vDS. Option D is incorrect because Network I/O Control regulates bandwidth allocation and does not cause connectivity loss; such issues would manifest as performance degradation rather than intermittent loss.
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.