Summary: Renumbering hosts of hosts

From: David Kuder (
Date: Wed Nov 21 1990 - 17:16:00 CST

Yesterday I asked about internet renumbering since we got a new internet
number. Of the responses that I got, the overwhelming majority feel that
the pain and agony of trying to do it incrementally doesn't match that
of just shutting everything down and renumbering. Barry Shein put it:
        Shut them all down and renumber them. Anything else will be madness

It is possible to do things incrementally. What I was thinking about and
which several folks felt was possible was to basically use routed and
ifconfig to tell machines that the one ethernet had two internets on it
and how to get from machines with old number to new and vice-versa. Of
course one has to be very careful or ugly things can happen.

Thanks to the following folks for their replies:
        tgsmith@East.Sun.COM (Timothy G. Smith) (Don Lewis)
        Russell Brand <wuthel!>
        beig@FRULM63.Bitnet (Jacques Beigbeder) (Bob Cunningham)
        mcs@mayo.EDU (Mahlon Stacy)
        "Dwight A. Ernest" <independent!> (Barry Shein)

The "best in show" answer goes to Bob Cunningham. He gave useful
pointers to doing it all at once and reminded of several things to
think about as I get ready to do it. His reply follows:

----- Begin Included Message -----

Date: Wed, 21 Nov 90 06:42:17 HST
From: (Bob Cunningham)
Message-Id: <>
Subject: Re: Renumbering hosts of hosts

Others may have better advice (I've only done that a couple of times:-).

In essence, you need to do these things:

        change the /etc/hosts files and/or your NIS/YP host maps
        change each machine's knowledge of it's interface (ifconfig)
        set up DNS tables (if you're going to be connected to the Internet)
        find and change any and all other references to the old numbers

The cleanest way is to edit/shutdown the reboot each machine, but
it's possible--though awkward--to do it "on the fly". Exact method
depends upon whether or not you're running NIS/YP

For an edit/shutdown approach, sequence it like this:

        edit /etc/hosts on each machine, then shut it down
        penultimate machines to change are your slave NIS/YP servers,
                trash the YP maps on each just befor shutdown
        last machine do do is the master NIS server

Startup sequence is in reverse:

        start up master NIS server single-user, set domain name,
                built master maps (including new host numbers!)
        then start up slave NIS servers
        then start up remainint machines

Without NIS, order doesn't matter (tho you'll have lots more editing to do!),
and you can bring up the machines right after you bring them down
(i.e., do a "shutdown -r").

With NIS, an alternative approach is to establish a new domainname,
with tables essentially the same but with new host numbers. Build
that NIS domain on some machine, and bring it up with new IP number.
On subsequent machines, edit /etc/hosts, change dommainname (in
/etc/rc.local and/or /etc/defaultdomain), then "shutdown -r".

To try it "on the fly", approach is similar to above, except that
instead of doing "shutdown -r", change the IP number associated
with each machines' ethernet interface via ifconfig.

However you do it, things to be careful of in the process are:

        gateway machines with multiple ethernet interfaces and thus
                multiple IP numbers
        NFS-mounted file systems (automounted or otherwise) as you
                bring machiens up & down
        email that may fall on the floor during the changeover

----- End Included Message -----

This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:05:59 CDT