Basic Concept: Split tunnel access routes do not automatically control DNS resolution. Split DNS must specify which domains use VPN-assigned DNS servers.
Why A is Correct: Configuring split DNS with internal corporate domains sends those queries to corporate DNS while leaving public browsing DNS local.
Why B is Wrong: DNS Proxy feature on the firewall to point clients to the gateway IP for DNS relates to VPN configuration, but it does not address the specific PAN-OS requirement for selectors, tunnel interface functions, routing, or Security policy in this scenario.
Why C is Wrong: "DNS Forwarding" option on the gateway's tunnel interface relates to VPN configuration, but it does not address the specific PAN-OS requirement for selectors, tunnel interface functions, routing, or Security policy in this scenario.
Why D is Wrong: NAT rule to allow DNS traffic from the GlobalProtect clients to the internal DNS servers relates to VPN configuration, but it does not address the specific PAN-OS requirement for selectors, tunnel interface functions, routing, or Security policy in this scenario.

The Transient zone type is used to allow traffic between zones in different virtual systems (VSYS) on a Palo Alto Networks firewall without the traffic leaving the firewall. It provides a way for virtual systems to communicate with each other by acting as a temporary or intermediary zone. Traffic can pass through the firewall between the virtual systems without requiring physical interfaces or leaving the device.

Establishing a functional IPSec VPN on a Palo Alto Networks Next-Generation Firewall requires addressing two distinct traffic flows: the management of the tunnel itself (Control Plane) and the transit of protected data (Data Plane).
First, to address the failure of the tunnel to establish, the firewall must have a security policy that permits the negotiation protocols. Specifically, a rule is required to allowike(UDP/500),ipsec-esp-udp(UDP/4500 if NAT- T is used), andipsec-esp(IP Protocol 50) between the source zone (where the firewall's public-facing interface resides) and the destination zone (where the partner's gateway resides). Since the firewall is the endpoint for this negotiation, the destination zone is often the "local" zone or the specific external zone where the peer's IP is located.
Second, once the tunnel is established, the firewall must be configured to allow the actual application traffic.
In the Palo Alto Networks zone-based architecture, traffic entering or exiting an IPSec tunnel is associated with aTunnel Interface. This interface must be assigned to a security zone. Because the default behavior for interzone traffic is to "Deny," the engineer must explicitly create a pair of security rules: one to allow traffic from the internal network zone to the tunnel interface's zone, and another to allow returning traffic from the tunnel interface's zone back to the internal zone. Without these rules, the tunnel may appear "active" in the logs, but all encapsulated production data will be dropped.

In this scenario, the customer requires that users do not directly access websites and that a security device (the firewall) manages the connection, while also ensuring that there is authentication back to the Active Directory (AD) servers for all sessions. The explicit proxy with Kerberos authentication is the best solution because:
The explicit proxy allows the firewall to intercept user web traffic and manage the connections on behalf of users.
Kerberos authentication ensures that the user's identity is validated against the Active Directory servers before the session is allowed, fulfilling the authentication requirement.

In a multi-vsys (Virtual System) architecture on a Palo Alto Networks firewall, communication between two virtual systems can occur internally through the firewall's backplane without requiring the traffic to exit through a physical interface to an external switch or router. To facilitate this internal routing, a specialized zone type is required.
While Layer 3 zones are used for standard routed traffic and are bound to physical or logical interfaces, the Externalzone type is specifically designed for inter-vsys communication. When an engineer configures two virtual systems to talk to one another, they must create a zone in each VSYS and set the Type toExternal.
These zones act as the logical "entry" and "exit" points for traffic crossing the VSYS boundary.
For the traffic flow to be successful, the Virtual Router in the source VSYS must have a route (typically a next-vr route) pointing to the Virtual Router in the destination VSYS. However, from a security policy perspective, the firewall sees the traffic as egressing the External zone of the source VSYS and ingressing the External zone of the destination VSYS. Without defining these zones asExternal, the firewall cannot logically associate the session with the internal backplane hand-off, and the traffic will be dropped despite having correct routing entries. This architectural requirement ensures that even internal virtual traffic remains subject to the firewall's zone-based security inspection.