Native Encapsulating Security Payload (ESP) uses Internet Protocol number ____; Network Address Translation Traversal (NAT-T) carries ESP using User Datagram Protocol (UDP) port ____.

### Why this is right\nNative ESP is identified by IP protocol 50. When NAT traversal is used, ESP is encapsulated in UDP, commonly on port 4500, so it can pass through a Network Address Translation device.\n\n### The concept\nAn IP protocol number identifies a protocol carried directly by IP, while a UDP port identifies an application or encapsulated traffic at the transport layer. Initial IKE negotiation commonly uses UDP 500, and NAT-T uses UDP 4500. NAT traversal is not the same as a source NAT policy for user traffic.\n\n### Terms\n- **ESP**: Encapsulating Security Payload, an IPsec traffic-protection protocol.\n- **NAT-T**: Network Address Translation Traversal, UDP encapsulation support for IPsec across NAT.\n- **UDP**: User Datagram Protocol, a transport protocol.\n\n### Remember\nNative ESP is IP protocol 50; NAT-T carries ESP in UDP 4500.