Users:
[ ] notify dns owners who we act as secondary for about the change.
    They will need to allow-transfer to the new IPs as well as old IPs
    to avoid disruption.  Also they will see change in IP address of
    my ns serving their domain, but to need to change ant config for
    that.

Firewall:
[ ] update firewall scripts on home box and other servers to allow
    all 4 IPs

Test for anything borked:
[ ] check that server answers dns, smtp, ssh, www requests on all
    public IPs
[ ] check axfr from my master dns using the relevant source address
[ ] check axfr from clients' master dns using the relevant src address
[ ] check my domains with dnsstuff.com

Named config:
[ ] configure outbound traffic with query-source, notify-source,
    transfer-source to force old IPs to be used
[ ] Re-do bork tests.

Interface config:
[ ] re-order interfaces on the box to make venet0:0/venet0:1 the new
    IPs, venet0:2/venet0:3 the old IPs.
[ ] Re-do bork tests.

Registrar changes:
[ ] update nameserver registration at the registrar.  NS records are
    now out of sync with the registrar, but that's okay.
[ ] Re-do bork tests.

Zone edits:
[ ] create new records for host3.mydomain.net & host4.mydomain.net
    with old IP addresses
[ ] assign new IPs to host1.mydomain.net & host2.mydomain.net
[ ] assign new multi-home IPs to host.mydomain.net
[ ] update all zones to use the new IPs for ns and mx records
[ ] Re-do bork tests.

Named config:
[ ] configure outbound traffic with query-source, notify-source,
    transfer-source to use new IPs
[ ] edit allow-transfer acl's on the master dns for new IPs
[ ] Re-do bork tests.

Interface config:
[ ] down venet0:2 and venet0:3
[ ] Re-do bork tests.

Users:
[ ] inform dns owners who we act as secondary for: change complete
    Wait for complaints... ;-)

When all is well:
[ ] delete host3.mydomain.net & host4.mydomain.net from zone
[ ] update firewall scripts on home box and other servers to allow
    just the 2 new IPs
[ ] Re-do bork tests.
[ ] check rDNS for old IPs has been blanked
[ ] let rapidvps know migration complete