How do I gracefully renumber an IP subnet ?

[Randy Witlicki]

  Hello,   this is the task I have to do:

  I have an IP subnet on the Internet which I have to
renumber due to a change at the upstream service provider.
  
  This is what is in place:
     - There are three domains in use (one is a subdomain)
on this subnet.
     - All the primary DNS nameservers are elsewhere.
     - Routing for both IP address blocks is now working.
     - The hosts now, or will soon have IP addresses in
both address spaces.  From elsewhere on the Internet I
can ping, traceroute, access IP ports on hosts which have
addresses in the new IP address block.
      - The router (a cisco 2501) has the old IP address as the
primary address and the new IP as the secondary.  The serial
link has been using "IP unnumbered" for a while and has not
needed any tinkering (so far).
      - Reverse DNS for both IP blocks is already setup.
      - The DNS TTL is set to 2 days.

 Here is the DNS transition plan that I have sketched out:

  Day 0:  Set DNS TTL to 1 hour for all affected IP addresses.

  Day 0 + 3 days:
     Change DNS addresses to new IP address block.
     Set DNS TTL back to 2 days.
     Reconfigure interfaces on router and hosts with new
IP addresses as primary and old addresses as secondary.

   About a week after this, the old IP address block will
be removed.

  Am I missing anything here ?

  Thanks in advance for any help and advice !

  - Randy     randy.witlicki  to the left of the at sign in the header
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