Chapter 7. Networks

One-two, one-two, and through and through The IMP-to-IMP went ACK and NACK, When the RFNM came, he said "I'm game," And sent the answer back,

Then hast thou joined the ARPANET? Oh come to me, my bankrupt boy! Quick, call the NIC! Send RFCs! He chortled in his joy.

”An excerpt from "ARPAWOCKY," D. L. Covill, May 1973 (RFC 527)

The gap between a systems administrator and a network administrator is often quite wide. Whereas a systems administrator is usually responsible for the hands-on management of a few hundred machines, perhaps in several buildings , a network administrator can easily be responsible for a network infrastructure that spans cities or states, from a high performance backbone down to the jacks at someone's desk. It is extremely rare to find someone who can play both positions well.

This chapter is aimed primarily at systems administrators who have little experience in networking, yet find themselves concerned that a performance problem is based in the network. This can be a quandary , particularly if there is no network engineer to be found! All of a sudden strange acronyms appear from the ether , and it can be hard to figure out what is going on. The foundation of performance tuning is understanding what the system is actually doing. This chapter provides an overview of network principles, encompassing the range from physical media all the way through to the TCP and UDP protocols. We'll then discuss the two most common file sharing mechanisms, NFS and CIFS. First, however, an important note about terminology.

The convention in the network world is to refer to data rates in mega bits per second (Mb/s), rather than the mega bytes per second (MB/s) common elsewhere in computing. In order to make a meaningful comparison, you must divide the number of Mb/s by eight. For example, a 10 Mb/s Ethernet connection transfers at most 1.25 MB/s.