hostnames and interfaces

Rob listone at
Fri Nov 21 00:39:05 PST 2003

My non-technical understanding:

* A BSD system has a fully qualified domain name that is set and
retrieved by the hostname(1) command. This is normally defined in
/etc/rc.conf and considered the 'true name' of the system. If this name
does not resolve to an IP address, many network services will complain
(such as sendmail). If this IP address is not configured on an interface
on the system, many things will get confused (such as routing).

* You can also configure other interfaces, either on extra network cards
or using the alias option of ifconfig(8). These interfaces should have
different IP addresses, and names are optional (but convenient).

* Any IP address can have extra names, either in /etc/hosts or on a
nameserver. The 'canonical' name should probably come first.

Your average BSD system will have 1 hostname that resolves to 1 address
configured on its single network interface. The /etc/hosts file will map
this address to the FQ hostname, and probably also to the short version
for convenience.

It will also have the name localhost, resolving to and
configured on lo0, again using /etc/hosts for resolution.

Anything beyond that is up to you...

----- Original Message -----
From: "paul van den bergen" <pvandenbergen at>
Subject: hostnames and interfaces

> hey all,
> I first encountered networking in CISCO land... where IP addresses and
> names seem to be associated...
> what is the freeBSD way?  AFAICS, a machine has a defined name
regardless of
> howmany interfaces it has.  if one splits the world up into hosts (one
> interface) and routers (multiple interfaces) can one define multiple
> hostnames?
> to expand on this, there is a potential many to many relationship here
> host names and IP addresses (strickly speaking that is what dns etc
> how dose BSD define this? how does one define this using BSD?
> --
> Dr Paul van den Bergen
> Centre for Advanced Internet Architectures
> pvandenbergen at
> IM:bulwynkl2002
> "And some run up hill and down dale, knapping the chucky stones
> to pieces wi' hammers, like so many road makers run daft.
> They say it is to see how the world was made."
> Sir Walter Scott, St. Ronan's Well 1824
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