LinuxSA Mailing list archives

  From: Mark Newton <newton@atdot.dotat.org>
  To  : Ben Donohue <donohueb@bvm.com.au>
  Date: Fri, 26 Mar 1999 17:04:55 +1030 (CST)

Re: moving a site and domain name from one ISP to another

Ben Donohue wrote:

 > can anyone help me with what is involved with moving a site from one ISP
 > to another ISP, such that it is done with the minimum of fuss and
 > downtime for the client. I'm moving a site, ie. a complete
 > www.name.com.au to another ISP, but want to keep the site up for as long
 > as possible. does the first ISP have to "release" the domain name and
 > then the second ISP take it up? is there a correct protocol for moving
 > the site?

Having just done this for myself (moving my permanent net link for
home from Camtech, my old employer, to Internode, my new one) and
having previously done it for several customers in my professional life,
I can provide a way of doing it with no disruption or downtime whatsoever.

1.  Bring up the link to the new ISP over a second line (i.e.: you'll
    be running both in parallel).

2.  Use IP aliasing to give yourself secondary IP addresses on each
    "important" machine which are inside the address allocation you
    got from your ISP.  Example:  I moved from 203.23.150.32/28 to
    150.101.89.0/28, so on my nameserver (203.23.150.35) I did something
    akin to this:

      ifconfig eth0:1 inet 150.101.89.3 netmask 255.255.255.240

    Now the machine responds to both its new *and* old IP address.
    Incoming packets to its old address come in via the old ISP,
    incoming packets to the new address come in via the new ISP.
    I also did something similar on the ethernet interface on my 
    router (but not its PPP interfaces).

3.  Alter your nameserver records to include new addresses for all
    your machines.  Remove the old addresses.  Renumber the machines
    to match what's in the DNS.  Change the default routes on all
    the machines to point to the new IP address for your router instead
    of the old one, and change the router's default gateway to point
    to the new ISP.

    Once you've done this, *all* your outbound traffic and most of your
    inbound traffic will go via the new ISP.  Incoming packets to your old 
    IP addresses, including your nameservers, will continue to arrive
    via the old ISP.  Note that this means you're using asymmetrical
    routing in many cases -- in via the old ISP, out via the new.

4.  Talk to whatever registry hosts your domain name (Internic, AUNIC,
    whatever) and do  whatever is necessary to tell them the IP address
    of your nameserver has changed.  Give them your nameserver's new
    IP address.  [ the procedure used for this varies from registry to
    registry ]

5.  Monitor the old net link (use tcpdump or mrtg or similar).  After a
    few days (after everyone's nameserver caches have expired) you should
    see that the old link remains totally quiescent because nameserver 
    lookups no longer occur over that link.  At that point it's safe to
    drop the link.

6.  Finish the job by removing the old IP addresses from your routers
    and nameservers altogether;  The new address should be the primary
    address on your interface instead of an aliased address.

I haven't actually rebooted any of my machines since switching over to
Internode, which is why I claim you can do it with no downtime or 
disruption whatever.  The only gotcha I found was that named needs
to be restarted when you add the ethernet alias on the nameserver, and
xdm needs to be restarted on any machine you renumber (otherwise you 
don't get a login window after an XDMCP prod;  You'll still get a 
login window on :0, though).

Cheers,

    - mark

--------------------------------------------------------------------
I tried an internal modem,                    newton@atdot.dotat.org
     but it hurt when I walked.                          Mark Newton
----- Voice: +61-4-1958-3414 ------------- Fax: +61-8-83034403 -----

-- 
Check out the LinuxSA web pages at http://www.linuxsa.org.au/
To unsubscribe from the LinuxSA list:
  mail linuxsa-request@linuxsa.org.au with "unsubscribe" as the subject