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[107.215.223.229]) by smtp.gmail.com with ESMTPSA id p16-20020a4ae150000000b0035f498be272sm2501496oot.13.2022.05.07.09.38.07 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 07 May 2022 09:38:08 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.80.82.1.1\)) From: Bakul Shah In-Reply-To: Date: Sat, 7 May 2022 09:38:07 -0700 Content-Transfer-Encoding: quoted-printable Message-Id: <727FE2A1-2E57-432B-8A3D-3249FA5AF29A@iitbombay.org> References: To: ron minnich X-Mailer: Apple Mail (2.3696.80.82.1.1) Subject: Re: [TUHS] conventions around zero padding in ip4 X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: TUHS main list Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" On May 7, 2022, at 9:14 AM, ron minnich wrote: >=20 > I first learned in the 80s that 127.1 meant 127.0.0.1. I always > assumed zero padding was defined in a standard *somewhere*, but am > finding out maybe not. I talked to the IP OG, and he tells me that > padding was not in any standard. [side note: it's weird and wonderful > to still have so many people "present at the creation" of computing as > we know it still around, and to find they are so willing to answer > naive questions!] >=20 > Padding is a standard in ip6, possibly because the addresses are so > long. :: is your friend. >=20 > IP4 padding came up recently: the ip command interprets 10.2 as > 10.2.0.0, whereas most things (golang libraries, ping, ...) interpret > it as 10.0.0.2. The latter interpretation accords with what I learned > 40y ago. >=20 > But, I find myself wondering: where was the first use of the IP4 zero > padding convention? =46rom RFC791: Addresses are fixed length of four octets (32 bits). An address begins with a network number, followed by local address (called the "rest" field). There are three formats or classes of internet addresses: in class a, the high order bit is zero, the next 7 bits are the network, and the last 24 bits are the local address; in class b, the high order two bits are one-zero, the next 14 bits are the network and the last 16 bits are the local address; in class c, the high order three bits are one-one-zero, the next 21 bits are the network and the last 8 bits are the local address. So n.m format =3D=3D network-number.local-address. The converse question = is who came up with the a.b.c.d format where each of a,b,c,d is in 0..255?=