Private use of non-RFC1918 IP space

Mon Feb 2 18:06:58 UTC 2009

> > > How does that help?  If you are renumbering due to a merger, couldn't
> > > you just agree on separate private space just as easily?
> > 
> > It would ensure that you could get the networks to communicate, without
> > IP address conflicts, *before* you started any renumbering.
> 
> Can you expand?  I assume that everyone understand VPNs so connecting
> over the Internet is not the issue.  If you pick a public IP block you
> still have to agree on that block.  How is using a public block
> different than agreeing on a private one?

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

Compare this with company A and B both using overlapping part of for
instance 192.168.0.0/16, and then merging. Conflict ensues, renumbering
or NATs required in order to connect the networks.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no