The answer is that the vDS port group for iSCSI does not have jumbo frames enabled, causing an MTU mismatch. When an ESXi host’s VMkernel interface (vmk1) is configured with an MTU of 9000 but the virtual distributed switch port group defaults to 1500, the iSCSI traffic fragments at the switch level, leading to high error rates and poor performance. On the VMware Certified Professional Data Center Virtualization VCP-DCV exam, this scenario tests your understanding that jumbo frames must be consistently enabled end-to-end—from the VMkernel adapter, through the vDS port group, to the physical network and iSCSI target. A common trap is assuming that setting MTU 9000 on the VMkernel alone is sufficient, but the port group’s MTU setting is a separate configuration that often gets overlooked. Remember the memory tip: “MTU must match from port to path”—verify the vDS port group MTU alongside the VMkernel adapter to avoid fragmentation.
VCP-DCV Configure and Manage vSphere Networking Practice Question
This VCP-DCV practice question tests your understanding of configure and manage vsphere networking. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
```
esxcli network ip interface list
vmk0
Name: vmk0
MAC Address: 00:50:56:60:00:01
Enabled: true
Portset: vSwitch0
Portgroup: Management Network
VDS Name: N/A
IP Address: 192.168.1.10
Subnet Mask: 255.255.255.0
MTU: 1500
vmk1
Name: vmk1
MAC Address: 00:50:56:60:00:02
Enabled: true
Portset: dvs1
Portgroup: iSCSI Network
VDS Name: dvs1
IP Address: 192.168.20.10
Subnet Mask: 255.255.255.0
MTU: 9000
```
An ESXi host has two VMkernel interfaces as shown in the exhibit. The iSCSI targets are on the same subnet as vmk1 and support jumbo frames. The administrator reports that iSCSI sessions are experiencing high error rates and poor performance. What is most likely the cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Refer to the exhibit.
```
esxcli network ip interface list
vmk0
Name: vmk0
MAC Address: 00:50:56:60:00:01
Enabled: true
Portset: vSwitch0
Portgroup: Management Network
VDS Name: N/A
IP Address: 192.168.1.10
Subnet Mask: 255.255.255.0
MTU: 1500
vmk1
Name: vmk1
MAC Address: 00:50:56:60:00:02
Enabled: true
Portset: dvs1
Portgroup: iSCSI Network
VDS Name: dvs1
IP Address: 192.168.20.10
Subnet Mask: 255.255.255.0
MTU: 9000
```
A
The management network (vmk0) is also using the vDS, causing traffic interference.
Why wrong: vmk0 is on a standard switch, not the vDS, so no interference.
B
The iSCSI VMkernel port should not be bound to a vDS.
Why wrong: iSCSI can use a vDS; binding to a vDS is not inherently problematic.
C
The iSCSI network (vmk1) is on a different subnet than the iSCSI targets.
Why wrong: The stem says targets are on the same subnet, so that's not an issue.
D
The vDS port group for iSCSI does not have jumbo frames enabled (MTU 9000).
If the vDS port group MTU is 1500, packets up to 9000 will be fragmented, causing errors. The VMkernel interface has MTU 9000, so the port group must match.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The vDS port group for iSCSI does not have jumbo frames enabled (MTU 9000).
Option C is correct because vmk1 is on a vDS (dvs1) and the exhibit shows MTU 9000, which is appropriate for jumbo frames. However, if the physical network is not configured for jumbo frames or the vDS port group MTU is not set to 9000, fragmentation may occur. The exhibit does not show vDS MTU, but the mismatch is a common cause of errors. Option A is incorrect because management traffic on vmk0 is separate and irrelevant. Option B is incorrect because different subnets are fine. Option D is incorrect because the iSCSI vmkernel port is dedicated.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 management network (vmk0) is also using the vDS, causing traffic interference.
Why it's wrong here
vmk0 is on a standard switch, not the vDS, so no interference.
✗
The iSCSI VMkernel port should not be bound to a vDS.
Why it's wrong here
iSCSI can use a vDS; binding to a vDS is not inherently problematic.
✗
The iSCSI network (vmk1) is on a different subnet than the iSCSI targets.
Why it's wrong here
The stem says targets are on the same subnet, so that's not an issue.
✓
The vDS port group for iSCSI does not have jumbo frames enabled (MTU 9000).
Why this is correct
If the vDS port group MTU is 1500, packets up to 9000 will be fragmented, causing errors. The VMkernel interface has MTU 9000, so the port group must match.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related VCP-DCV subnetting questions on CIDR, address ranges, and subnet selection.
Configure and Manage vSphere Networking — This question tests Configure and Manage vSphere Networking — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The vDS port group for iSCSI does not have jumbo frames enabled (MTU 9000). — Option C is correct because vmk1 is on a vDS (dvs1) and the exhibit shows MTU 9000, which is appropriate for jumbo frames. However, if the physical network is not configured for jumbo frames or the vDS port group MTU is not set to 9000, fragmentation may occur. The exhibit does not show vDS MTU, but the mismatch is a common cause of errors. Option A is incorrect because management traffic on vmk0 is separate and irrelevant. Option B is incorrect because different subnets are fine. Option D is incorrect because the iSCSI vmkernel port is dedicated.
What should I do if I get this VCP-DCV question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related VCP-DCV subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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