The Cisco network-based virtual firewall service solution helps service providers to deliver costeffective, scalable, integrated security services for enterprise customers using Cisco platforms .What is a virtual firewall?（）

• A、another name for a firewall deployed in routed mode
• B、another name for a firewall deployed in transparent mode
• C、a separation of multiple firewall security contexts on a single firewall
• D、a firewall that, when deployed in routed mode, can support up to 1000 VLANs per context