what to do after an IP change

[James Wilkinson]

Jeff Vian wrote:
> Also, when doing an install with FC2, FC1, and earlier RedHat versions,
> the hostname given during the install is (in my experience) usually also
> placed on the 127.0.0.1 line of this file.  I consider it a bug (but
> only a minor annoyance) that the assigned hostname is not placed on its
> own line with the assigned IP address, but in cases where there are
> multiple NICs it is harder to get it right so the present method may be
> best.  

Well, once you've got the hostname associated with the 127.0.0.1 IP
address, then everything works perfectly well with it. You ping your
hostname, and your hostname replies.

In the old days, it used to be better for performance, at least on some
Unix-alikes: using 127.0.0.1 meant that the packets never had to go
anywhere near the Ethernet layer. I understood there were some IP stacks
where the packets would get to the NIC before coming back "up" to the
IP stack. With slow processors and the ISA bus, that was a big deal.

With faster buses, faster CPUs and smarter stacks, that probably isn't
a problem any more. (I'm don't know about the history of the Linux IP
stack is here, though).

These days, it's probably more of a security benefit for the less
security-conscious. Many Fedora daemons, by default, now only listen
to 127.0.0.1, and iptables will often get the rest. Having the local
hostname point there means that anything local that does want to use
such services will Just Work.

Or to put it another way, it means you can SMTP mail to your hostname
using the standard sendmail setup, which is set not to listen on any
other ports. If the hostname pointed to an external IP address,
people would use it, find that sendmail wasn't listening, and be
tempted to make sendmail listen on external IP addresses rather than
send the e-mail to localhost.

The only "bug" I can think of is that it's not what you personally
expect.

Comments?

James.

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