On which protocol number does Encapsulating Security Payload operate?

A.
06

B.
47

C.
50

D.
51

Explanation:
Encapsulating Security Payload (ESP) is a member of the IPsec protocol suite. In IPsec it provides
origin authenticity, integrity and confidentiality protection of packets. ESP also supports
encryption-only and authentication-only configurations, but using encryption without authentication
is strongly discouraged because it is insecure. Unlike Authentication Header (AH), ESP in
transport mode does not provide integrity and authentication for the entire IP packet. However, in
Tunnel Mode, where the entire original IP packet is encapsulated with a new packet header
added, ESP protection is afforded to the whole inner IP packet (including the inner header) while
the outer header (including any outer IPv4 options or IPv6 extension headers) remains
unprotected. ESP operates directly on top of IP, using IP protocol number 50.
Reference: http://en.wikipedia.org/wiki/IPsec