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/etc/protocols
The /etc/protocols file lists all of the standard Internet protocols your OpenBSD system knows about. Each protocol has an assigned number, and various programs use these numbers to determine how they handle transactions. Almost all Internet transactions happen over TCP or UDP. Most people don't realize that TCP is protocol 6, UDP is protocol 17, and there are dozens of other protocols. Some protocols are very heavily used in particular environments, and others are so outdated that you'll almost certainly never encounter them. As a systems administrator you don't have to be intimately familiar with every piddly little protocol out there, but you should know that the world is bigger than TCP/IP. Each protocol has its own line in /etc/protocols. The first entry on a line is the official name. The second entry is the protocol number. Following that are any aliases for the protocol. Finally, comments are set off with a pound sign. Just for amusement, here's a snippet of /etc/protocols.tcf 87 TCF # TCFigrp 88 IGRP # IGRP
ospf 89 OSPFIGP # Open Shortest Path First IGP
Some of you may have heard of OSPF, and a few of those may have even heard of IGRP. I have absolutely no clue what TCF is, and even the almighty Google leads me only to a thousand copies of /etc/protocols when I ask about it. If I was really interested, I could research and find out, but at the moment I don't particularly care. If protocol number 87 shows up knocking at my firewall one day, however, I can at least put a name to it before starting the journey.
