2 # Internet (IP) protocols
3 ip 0 IP # internet protocol, pseudo protocol number
4 icmp 1 ICMP # internet control message protocol
5 igmp 2 IGMP # Internet Group Management
6 tcp 6 TCP # transmission control protocol
7 udp 17 UDP # user datagram protocol
9 gre 47 GRE # Generic Routing Encapsulation
10 ah 51 AH # authentication header
11 ospf 89 OSPFIGP # Open Shortest Path First IGP
12 pim 103 PIM # Protocol Independent Multicast
13 vrrp 112 VRRP # Virtual Router Redundancy Protocol