usr/src/etc/protocols

#
# Internet (IP) protocols
#
#       @(#)protocols   5.1 (Berkeley) %G%
#
ip      0       IP              # internet protocol, pseudo protocol number
icmp    1       ICMP            # internet control message protocol
ggp     3       GGP             # gateway-gateway protocol
tcp     6       TCP             # transmission control protocol
egp     8       EGP             # exterior gateway protocol
pup     12      PUP             # PARC universal packet protocol
udp     17      UDP             # user datagram protocol
hmp     20      HMP             # host monitoring protocol
xns-idp 22      XNS-IDP         # Xerox NS IDP
rdp     27      RDP             # "reliable datagram" protocol