Okay, I'm starting to "get" how network configuration is supposed to 
work. (Call me dense -- it's only taken several years as a casual user and 
occasional my-system-administrator to figure out this much.) It looks like 
the sysconfig.txt file (in /usr/share/doc/initscripts-* on RedHat systems?) 
has the *best" documentation, but I'm not convinced it is always correct.
     How does this sound?

1) /etc/sysconfig/network is the most basic of networking configuration files 
and it says whether or not you want networking. At a minimum, this file may 
have a single line in it (as mine now does):
NETWORKING=yes
It also makes sense (to me) to define the system's gateway if this is 
hard-coded for the system. But since many users will be getting a lot of 
their networking configuration via DHCP (including gateway information), then 
it appears /etc/sysconfig/network is probably not the common place to specify 
gateway information.
Some system installation tools automatically put the HOSTNAME=xxxxx.yyyyy host 
name (xxxxx) and domain name (yyyyy) here. This, however, may be less than 
optimal as we'll see in #3 below (and this was one of the contributing 
elements to my long-standing problem with slow booting).
So, although it is possible to have additional parameters in the  
/etc/sysconfig/network file, it is probably better not to do so. For this 
file, "less is better".

2) /etc/sysconfig/network-scripts/ifcfg-* files (such as ifcfg-eth0) contain 
network configuration for specific interfaces network(s). This would be the 
place to specify, for example, how that specific interface gets it IP 
address. Does it come via a DHCP server (BOOTPROTO=dhcp) or it is hard-coded 
(BOOTPROTO=none, and IPADDR=aaa.bbb.ccc.ddd, and so forth).
HOSTNAME=xxxxxx *could* be specified in this file but this is clearly less 
than ideal since we're dealing with a specific network interface rather than 
the system in general.

3) /etc/nsswitch defines the order in which local and external resources are 
to be used in resolving system and domain names. The "best" configuration 
depends on several factors that are, at the moment, beyond my ability to 
enumerate completely but, nonetheless, here are the common cases that come to 
mind:
3A) user with a single computer booting "without network" and connecting, 
occasionally, via dial-up to an ISP.
3B.1) user with a small number of computers permanently interconnected with a 
"firewall" that hands-out IPs and other networking information (via DHCP) as 
each of these computers boot.
3B.2) same as 3B.1 but for the box with the DHCP server -- and there are two 
sub-cases here, I guess: dial-up or permanent internet connection.
3C) administrator handling a large number of computers (probably in a 
corporate environment).
3D) other settings which my feeble mind doesn't grasp as significant.

4) /etc/hosts now appears to me to have a central role in a couple of 
different ways. First, when I type in a host.domainname, it is one of the 
places my system is going to look to try and determine the IP address to 
contact. Secondly, but actually much earlier in the system's life-time, it is 
the place that various components of the system are going to look to 
determine the system's host.domainname and, not long thereafter when starting 
up sendmail for example, to back-translate that same name to discover if that 
host.domainname is valid (and what IP is associated with it). (A 
misconfigured /etc/hosts is the other contributor to the annoying boot-up 
times I *was* seeing.)
For relatively small networks behind a firewall (such as mine), /etc/hosts 
tends to be created once and then copied from system to system within the 
small network such that all systems know everyone else's IPs and names (wthin 
the small network). Obviously there is room for error if /etc/host isn't kept 
up to date on all systems in the small network but, nonetheless, it is a 
relatively easy way for a novice to "make it work."
A more sophisticated administrator (but not poor me) would set up a DNS within 
the small network and relegate the /etc/hosts file on each system to a much 
smaller role. (Does the minimum content then become "127.0.0.1 
localhost.localdomain localhost"?)

How'm I doin'? Anyone care to comment / correct / clarify anything here? And 
does anyone know of a "good" tutorial on this (because I haven't found one 
yet)?

-- 
Ed Skinner, ed@flat5.net, http://www.flat5.net/

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