Which tool facilitates a customer's migration from existing legacy firewalls to Palo Alto Networks Next-Generation...

Why A is correct: Expedition is a tool specifically designed to automate the migration of configurations from various legacy firewalls to Palo Alto Networks NGFWs. It helps parse existing configurations and translate them into PAN-OS policies.  

Why B, C, and D are incorrect:

B: Policy Optimizer helps refine existing PAN-OS policies but doesn't handle migration from other vendors.

C: AutoFocus is a threat intelligence service, not a migration tool.  

D: IronSkillet is a collection of security best-practice configurations for PAN-OS, not a migration tool.

Palo Alto Networks References: The Expedition documentation and datasheets explicitly describe its role in firewall migrations.