[ih] The netmask

[Matt Mathis]

I believe Philip Almquist explicitly studied tradeoffs in mask designs, and
that his wisdom is embodied in RFC 1380.   However that document does not
mention discarded designs.

The point I remember from a hallway conversation was about the
computational complexity of resolving "longest match" (or some other route
selection algorithm) with non-contiguous masks.  It may be that this point
alone precluded all designs other than contiguous masks.

Look for Archives of the IETF ROAD (Routing + Addressing) group.

Thanks,
--MM--
Evil is defined by mortals who think they know "The Truth" and use force to
apply it to others.
-------------------------------------------
Matt Mathis  (Email is best)
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On Tue, Jan 7, 2025 at 1:24 PM Grant Taylor via Internet-history <
internet-history at elists.isoc.org> wrote:

> On 1/7/25 12:02 PM, Andrew G. Malis via Internet-history wrote:
> > While the RFC refers to bit-masks, operationally people realized that
> > since CIDR bit-masks were always all ones from the left and all zeros
> > from the right, they could be equivalently represented by an integer
> > count of one bits, usually following a "/" character.
>
> I don't know if CIDR itself codified (sub)netmasks being sequential ones
> or not.  But I do know that some older TCP/IP implementations would work
> with netmasks that were non-contiguous ones.
>
> I remember some early discussions about being EXTREMELY creative with
> non-contiguous bit patterns in netmasks in the mid-to-late '90s.  In
> retrospect, I'm glad that we settled on the simpler convention of
> contiguous ones.
>
>
>
> --
> Grant. . . .
> unix || die
>
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