This chapter covered three primary topics: subnetting, mail services, and TCP/IP utilities.
Subnetting is the process by were a single IP address can be split into more sub-nets. This is great (for example) for large networks that use a significant potion of their private IP space. It's also good for added security, improved performance, and simplified troubleshooting. Subnetting is a achieved through a process which ANDs the binary value of an IP address with another block of 4 octets called the subnet mask to provide a subnet address.
TCP/IP mail services are what one would expect – email. However, it's not quite that cut and dried. SMTP (Simple Mail Transfer Protocol) is the protocol for moving email around, among other things, the Internet. It operates over port 25 and uses a format called MIME (Multipurpose Internet Mail Extensions). MIME was released by the IEEE in 1992 to make email more versatile. Before MIME you couldn't for example, include pictures in an email. (You couldn't include malware, either, but hey, you have to take the bad with the good.) There's also POP (Post Office Protocol) which operates over port 110. Also out there is IMAP (Internet message Access Protocol) which was developed as a more sophisticated option over P POP3. It can replace POP3 without changing programs.
The final portion of the chapter covered utilities like traceroute, host, dig, and netstat that are used for setting up and troubleshooting a network.
Reading this chapter, it finally started to sink in why it's possible to make a living doing this stuff – to a layperson, a lot of this must be dauntingly arcane.
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