The answer is to set 'Forged transmits' to 'Reject'. This security policy on a vSphere Distributed Switch prevents MAC impersonation by dropping any outbound frames where the source MAC address does not match the one assigned to the virtual NIC, effectively blocking a VM from spoofing another device’s identity. On the VCP-DCV exam, this question tests your understanding of the three vDS security policies—promiscuous mode, MAC address changes, and forged transmits—and the common trap is confusing 'MAC address changes' (which controls inbound changes to the effective MAC) with 'Forged transmits' (which controls outbound impersonation). A reliable memory tip is to think of 'Forged transmits' as the outbound guard: if a VM tries to send a frame with a fake source MAC, it gets rejected, just like a forged signature on a check.
VCP-DCV Configure and Manage vSphere Networking Practice Question
This VCP-DCV practice question tests your understanding of configure and manage vsphere networking. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An organization has deployed a vSphere Distributed Switch (vDS) across multiple ESXi hosts. The security team requires that no virtual machine can change its MAC address to impersonate another device. Which security policy setting on the distributed port group should be configured to fulfill this requirement?
When forged transmits is rejected, the vSwitch drops frames that do not originate from the VM's actual MAC address, thus preventing MAC spoofing.
B
Set 'MAC address changes' to 'Reject'.
Why wrong: This policy controls whether the VM guest OS can change the MAC address (e.g., via software), but it does not prevent the VM from sending frames with a forged source MAC.
C
Set 'Promiscuous mode' to 'Reject'.
Why wrong: Promiscuous mode rejection prevents the VM from receiving frames not destined for it, but does not prevent MAC impersonation.
D
Enable traffic shaping and set a low average bandwidth.
Why wrong: Traffic shaping controls bandwidth usage, not security or MAC behavior.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set 'Forged transmits' to 'Reject'.
Option B is correct because the 'Forged transmits' policy, when set to 'Reject', drops any outbound frames with a source MAC address different from the one assigned to the virtual NIC. This prevents MAC impersonation. Option A is incorrect because 'Promiscuous mode' allows the VM to see all traffic on the port, which is a security risk and unrelated to MAC impersonation. Option C is incorrect because 'MAC address changes' controls whether the VM can change its effective MAC address, but the question is about outward impersonation. Option D is incorrect because traffic shaping limits bandwidth, not MAC security.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Set 'Forged transmits' to 'Reject'.
Why this is correct
When forged transmits is rejected, the vSwitch drops frames that do not originate from the VM's actual MAC address, thus preventing MAC spoofing.
Related concept
Static NAT maps one inside address to one outside address.
✗
Set 'MAC address changes' to 'Reject'.
Why it's wrong here
This policy controls whether the VM guest OS can change the MAC address (e.g., via software), but it does not prevent the VM from sending frames with a forged source MAC.
✗
Set 'Promiscuous mode' to 'Reject'.
Why it's wrong here
Promiscuous mode rejection prevents the VM from receiving frames not destined for it, but does not prevent MAC impersonation.
✗
Enable traffic shaping and set a low average bandwidth.
Why it's wrong here
Traffic shaping controls bandwidth usage, not security or MAC behavior.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related VCP-DCV NAT questions on configuration and troubleshooting.
Configure and Manage vSphere Networking — This question tests Configure and Manage vSphere Networking — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Set 'Forged transmits' to 'Reject'. — Option B is correct because the 'Forged transmits' policy, when set to 'Reject', drops any outbound frames with a source MAC address different from the one assigned to the virtual NIC. This prevents MAC impersonation. Option A is incorrect because 'Promiscuous mode' allows the VM to see all traffic on the port, which is a security risk and unrelated to MAC impersonation. Option C is incorrect because 'MAC address changes' controls whether the VM can change its effective MAC address, but the question is about outward impersonation. Option D is incorrect because traffic shaping limits bandwidth, not MAC security.
What should I do if I get this VCP-DCV question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related VCP-DCV NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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