该文件是网络协议定义文件，里面记录了TCP/IP协议族的所有协议类型。文件中的每一行对应一个协议类型，它有3个字段，中间用TAB或空格分隔，分别表示“协议名称”、“协议号”和“协议别名”。下面是该文件的节选内容。

# Internet (IP) protocols
#
# Updated from http://www.iana.org/assignments/protocol-numbers and other
# sources.
# New protocols will be added on request if they have been officially
# assigned by IANA and are not historical.
# If you need a huge list of used numbers please install the nmap package.

ip      0       IP              # internet protocol, pseudo protocol number
#hopopt 0       HOPOPT          # IPv6 Hop-by-Hop Option [RFC1883]
icmp    1       ICMP            # internet control message protocol
igmp    2       IGMP            # Internet Group Management
ggp     3       GGP             # gateway-gateway protocol
ipencap 4       IP-ENCAP        # IP encapsulated in IP (officially ``IP'')
st      5       ST              # ST datagram mode
tcp     6       TCP             # transmission control protocol
egp     8       EGP             # exterior gateway protocol
igp     9       IGP             # any private interior gateway (Cisco)
pup     12      PUP             # PARC universal packet protocol

不要对该文件进行任何修改。