[conspire] Migration plan for moving IP addresses

Bill Moseley moseley at hank.org
Mon Aug 18 09:23:04 PDT 2008

At my home office I have DSL with a /29.  The speed is horrible and
I'm looking at moving to a business account with Comcast Cable.  Yes,
scares me a bit.

My current setup is a /29 that comes into a switch and then to a
number of machines (with public IP addresses).  (Then NAT from a few
of those machines to inside LANs).  My switch is not managed -- just
an inexpensive small business grade switch -- and does not have any
kind of filtering.

My question is how to manage the change in IP numbers smoothly.

I suspect I'll want my servers to respond to both the old and new IPs
for a time.

I assume I can just configure my machines to listen to both the old
and new IP addresses during the transition.  And then just plug the
new ethernet cable right into my existing switch along with the
existing DSL ethernet.

What I'm not clear on is if I need to alter my routing tables, or if
my switch will deal with this.  I suspect I want to avoid asymmetric
routing (and I also suspect the two ISPs won't pass my packets with a
different source IP).

Anyone have experience with this?  Is this something where I'd need to
use iproute (v2)?

Frankly, I can afford a few hours of downtime -- so yanking the DSL,
and reconfiguring with the new IP addresses would not be horrible, but
IIRC, the TTL for the root name servers is a day, so there could be
significant time where queries (and cached dsn) are trying to get to
the old IPs.

Anyone been through this?  Still have your migration plans around?


Bill Moseley
moseley at hank.org
Sent from my iMutt

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