Private use of non-RFC1918 IP space

D'Arcy J.M. Cain darcy at
Mon Feb 2 18:30:47 UTC 2009

On Mon, 02 Feb 2009 19:06:58 +0100 (CET)
sthaug at wrote:
> Company A uses public IP block A internally. Company B uses public IP

OK, so we start out with a bad network design then.

> block B internally. Company A and B later merge, and connect their
> networks. No conflict, no renumbering needed (at least not right away).

Maybe.  What if they both happened to choose  Is this just a
matter of decreasing the odds of a conflict?  It still seems like bad
network management to me.

> Compare this with company A and B both using overlapping part of for
> instance, and then merging. Conflict ensues, renumbering
> or NATs required in order to connect the networks.

Right.  One side needs to change a config file in their DHCP server and
maybe their internal DNS.  If they need to change much more than that
then its time for a network re-engineering anyway.

D'Arcy J.M. Cain <darcy at>         |  Democracy is three wolves                |  and a sheep voting on
+1 416 425 1212     (DoD#0082)    (eNTP)   |  what's for dinner.

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