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/
---------------------------------------------------
PLUG-discuss mailing list -
PLUG-discuss@lists.plug.phoenix.az.us
To subscribe, unsubscribe, or to change you mail settings:
http://lists.PLUG.phoenix.az.us/mailman/listinfo/plug-discuss
(text/plain)