Private use of non-RFC1918 IP space

sthaug at sthaug at
Mon Feb 2 18:55:49 UTC 2009

> > Company A uses public IP block A internally. Company B uses public IP
> OK, so we start out with a bad network design then.

No. We start with blocks A and B which are both properly allocated by
the relevant addressing authorities.

> > 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.

My assumption throughout this whole discussion, which clearly has not
been understood, is that the public IP block used internally is a
properly allocated by the relevant addressing authority. That is, for
me, the whole point of using public addresses to guarantee uniqueness.

Steinar Haug, Nethelp consulting, sthaug at

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