Stupid Question maybe?

Wed Dec 19 15:19:28 UTC 2018

On 12/18/18 8:38 PM, Fred Baker wrote:
> On Dec 19, 2018, at 3:50 AM, Brian Kantor <Brian at ampr.org> wrote:
>> /24 is certainly cleaner than 255.255.255.0.
>>
>> I seem to remember it was Phil Karn who in the early 80's suggested
>> that expressing subnet masks as the number of bits from the top end
>> of the address word was efficient, since subnet masks were always
>> a series of ones followd by zeros with no interspersing, which
>> was incorporated (or independently invented) about a decade later
>> as CIDR a.b.c.d/n notation in RFC1519.
>> 	- Brian
> 
> Actually, not really. In the time frame, there was quite a bit of discussion about "discontiguous" subnet masks, which were masks that had at least one zero somewhere within the field of ones. There were some who thought they were pretty important. I don't recall whether it was Phil that suggested what we now call "prefixes" with a "prefix length", but it was not fait accompli.
> 
Actually, Brian is correct.  Phil was w-a-y ahead of the times.  But I don't
remember him talking about it until the late '80s.  Brian probably knew him longer.

Anyway, Fred is also correct.  It took many years, and a lot of argument, before
prefixes were common.  Partly that was me, in PIPE/SIP/SIPP and CIDRD.  Required
longest prefix match in early Neighbor Discovery drafts.

However, I was more of an advocate for suffixes, also known as host mask, wanting
them to be common between IPv4 and IPv6.  I still think it would have simplified
setup for operators.  Most don't care how long the network part, they know how
many nodes are needed on the LAN.

Cisco had adopted /n for network prefixes, so I'd proposed //h for host suffixes.
Anyway, /n made it into RFCs.

> Going with prefixes as we now describe them certainly simplified a lot of things.
> 
> Take a glance at https://www.google.com/search?q=discontiguous+subnet+masks for a history discussion.
> 
Didn't see anything ancient.  Circa 2010 arguments....  Apparently, CIDRD archives
aren't up anymore.