hopopt 0 HOPOPT # IPv6 Hop-by-Hop Option
icmp 1 ICMP # Internet Control Message
igmp 2 IGMP # Internet Group Management
ggp 3 GGP # Gateway-to-Gateway
ip 4 IP # IP in IP (encapsulation)
st 5 ST # Stream
tcp 6 TCP # Transmission Control
cbt 7 CBT # CBT
egp 8 EGP # Exterior Gateway Protocol
[ ... ]
chaos 16 CHAOS # Chaos
udp 17 UDP # User Datagram