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PCNSA Practice Question: A large financial institution runs a PA-5250…
A large financial institution runs a PA-5250 firewall in a virtual wire mode between two core switches. The firewall is configured with multiple virtual wire sub-interfaces to segregate traffic for different VLANs. Recently, the security team noticed that multicast traffic from a critical trading application is not being forwarded across the virtual wire link. The firewall has multicast policies enabled, and the trading application uses IGMPv3. The administrator has verified that the firewall's multicast policy allows the traffic and that the IGMP snooping is enabled on the adjacent switches. However, the multicast stream does not reach the receivers on the other side. Which step should the administrator take to resolve this issue?
⚠ Common exam trap
Watch out — candidates often assume enabling multicast policies alone is sufficient for forwarding, overlooking that virtual wire mode requires explicit IGMP snooping configuration on the firewall's sub-interfaces to bridge multicast traffic between VLANs.
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
✓
Enable IGMP snooping on the virtual wire sub-interfaces of the firewall.
In a virtual wire deployment, the firewall does not participate in Layer 2 protocols like IGMP snooping by default. Even if multicast policies are enabled, the firewall must explicitly perform IGMP snooping on its virtual wire sub-interfaces to track multicast group memberships and forward the traffic correctly. Enabling IGMP snooping on the sub-interfaces allows the firewall to intercept IGMPv3 membership reports and build the necessary forwarding state for the multicast stream.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the multicast traffic bandwidth limit in the QoS policy.
Why it's wrong here
QoS bandwidth limits do not affect multicast forwarding; the issue is that the firewall is not forwarding at all.
- ✗
Change the virtual wire mode to layer 3 mode and configure PIM.
Why it's wrong here
Changing the mode would require major reconfiguration and break the transparent nature of the deployment. PIM is not necessary if the firewall is in virtual wire mode.
- ✗
Configure a static multicast MAC address mapping on the firewall.
Why it's wrong here
Static MAC mapping is not needed; the issue is that the firewall is not learning multicast group memberships dynamically.
- ✓
Enable IGMP snooping on the virtual wire sub-interfaces of the firewall.
Why this is correct
IGMP snooping allows the firewall to listen to IGMP reports and build a multicast forwarding table, enabling it to forward multicast traffic to the correct ports.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNSA practice question is part of Courseiva's free Palo Alto Networks 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 PCNSA exam.