See inet_addr(3) - the history section in the NetBSD man pages says 4.2 BSD. https://man.netbsd.org/inet_addr.3 Speculation: it would not surprise me to find that the "a.b" form turning into "a.0.0.b" was a convenience for ARPANET - ucb-arpa (DEC VAX-11/780) address was 10.0.0.78 or 0/78 in the old form: host 0 on IMP 78, as seen below in an ARPANET hosts file from November 1982 that I have saved (that's just before the Jan 1, 1983 NCP-to-IP transition that heralded the operational beginning of the Internet). The file is sorted in IMP number order. Erik : Updated on Mon Nov 15 18:59:52 PST 1982 NET arpanet 10 arpa ; 258 known hosts NET nonet 0 nonet ; anyhost 0/0,nonet nonet ucla-ats 0/1,arpanet ucla-ccn 1/1,arpanet ccn ucla-security 2/1,arpanet ucla-s ucla-net ucla-locus 3/1,arpanet sri-nsc11 0/2,arpanet nsc11 dnsri sri-kl 1/2,arpanet sri kl sri-csl 2/2,arpanet sri-vis11 sri-f2 f2 csl sri-tsc 3/2,arpanet sri-tscb tscb nosc-cc 0/3,arpanet nuc-cc nosc-elf nosc nosc-spel 1/3,arpanet nosc-secure1 logicon 2/3,arpanet nprdc 3/3,arpanet nprdc-unix nprdc-atts utah-tac 2/4,arpanet utah-20 3/4,arpanet bbnf 0/5,arpanet bbn-tenexf bbng 1/5,arpanet bbn-tenexg bbna 3/5,arpanet bbn-tenexa mit-multics 0/6,arpanet multics mit-dms 1/6,arpanet dms mit-ai 2/6,arpanet ai mit-ml 3/6,arpanet ml rand-relay 1/7,arpanet cs-rand rand-cs rand-tac 2/7,arpanet rand-unix 3/7,arpanet rand-ai nrl 0/8,arpanet nswc-wo 2/8,arpanet nrl-tops10 3/8,arpanet nrl-css 7/8,arpanet nrl-csd harv-10 0/9,arpanet acl yale 2/9,arpanet ll 0/10,arpanet ll-tcp 1/10,arpanet ll-xn 2/10,arpanet ll-11 3/10,arpanet su-ai 0/11,arpanet sail su-tac 2/11,arpanet su-score 3/11,arpanet score dti-vms 0/12,arpanet dti 1/12,arpanet gunter-unix 0/13,arpanet gafs gunter-adam 1/13,arpanet gunter-tac 2/13,arpanet gunt cmu-cs-b 0/14,arpanet cmu-10b cmub cmu-cs-a 1/14,arpanet cmu-10a cmua cmu-cs-c 3/14,arpanet cmu-20c cmuc ames-67 0/16,arpanet ames ames-tip 2/16,arpanet ames-11 3/16,arpanet mitre 0/17,arpanet mitre-tac 2/17,arpanet dcn1 3/17,arpanet linkabit radc-multics 0/18,arpanet radc radc-xper 1/18,arpanet xper radc-tac 2/18,arpanet radt radc-tops20 3/18,arpanet radc-20 rochester 4/18,arpanet roch radc-unix 5/18,arpanet nbs-vms 0/19,arpanet nbs-10 nbs nbs-sdc 1/19,arpanet nbs-unix 2/19,arpanet nbs-pl 3/19,arpanet cctc 0/20,arpanet dcec-tac 2/20,arpanet edn-unix 3/20,arpanet lll-unix 0/21,arpanet lll-comp lll-mfe 1/21,arpanet mfe isi-speech11 0/22,arpanet usc-isi 1/22,arpanet usc-isia isia isi usc-isic isic usc-eclb 0/23,arpanet eclb usc-eclc 1/23,arpanet eclc usc-tac 2/23,arpanet usc-ecl 3/23,arpanet ecl usc-ecla ecla nadc 2/24,arpanet wharton-10 3/24,arpanet wharton seismo 0/25,arpanet pentagon-tip 2/26,arpanet pent-unix 3/26,arpanet usc-isid 0/27,arpanet isid isi-png11 1/27,arpanet isi-vaxa 2/27,arpanet vaxa arpa-dms 0/28,arpanet arpa-tac1 1/28,arpanet arpa-tac2 2/28,arpanet arpa-png11 3/28,arpanet arpa-xgp11 brl 0/29,arpanet brl-tac 2/29,arpanet brl-bmd 3/29,arpanet bmd70 cca-unix 0/31,arpanet cca cca-tenex cca-vms 1/31,arpanet cca-tac 2/31,arpanet mit-devmultics 3/31,arpanet devmultics cisl parc-maxc 0/32,arpanet parc parc-maxc1 parc-maxc2 kestrel 3/32,arpanet sci-ics sci kes sct nps 0/33,arpanet fnoc 1/33,arpanet fnwc nps-tac 2/33,arpanet fnoc-secure 3/33,arpanet fnwc-secure lbl 0/34,arpanet lbl-unix 1/34,arpanet nosc-secure2 0/35,arpanet usc-isir1 isir1 nosc-sdl 1/35,arpanet nelc-elf nelc accat-tac 2/35,arpanet nelc-tip nosc-secure3 3/35,arpanet coins-tas 0/36,arpanet cincpacflt-wm 1/36,arpanet cincpac-tac 2/36,arpanet purdue 0/37,arpanet purdue-cs purdue-ncp csnet-purdue 2/37,arpanet purdue-rvax rvax bragg-sta1 1/38,arpanet bragg-tac 2/38,arpanet src-ccp 0/39,arpanet sdac-ccp src-unix 1/39,arpanet sdac-unix src-nep 2/39,arpanet sdac-nep bbn40-tac 0/40,arpanet ncc-tac 2/40,arpanet office-1 0/43,arpanet of1 office-2 1/43,arpanet of2 office off office-3 2/43,arpanet of3 almsa office-7 3/43,arpanet of7 cecom mit-xx 0/44,arpanet xx ll-asg 1/44,arpanet mit-tstgw 2/44,arpanet mit-mc 3/44,arpanet mc collins-pr 0/46,arpanet collins-tac 2/46,arpanet okc-unix 3/46,arpanet wpafb 0/47,arpanet wpafb-afwal 1/47,arpanet avsail wpafb-afal wpafb-tip 2/47,arpanet afwl 0/48,arpanet afwl-tip 2/48,arpanet bbnb 0/49,arpanet bbn-tenexb bbnc 3/49,arpanet bbn bbn-tenex darcom-tac 2/50,arpanet sri-unix 2/51,arpanet ada-vax 0/52,arpanet isi-vaxb ajpo vaxb usc-isie 1/52,arpanet isie usc-isif 2/52,arpanet isif usc-isib 3/52,arpanet isib afsc-ad 0/53,arpanet eglin ncsc 1/53,arpanet ncsl afsc-dev 2/53,arpanet eglin-dev martin 3/53,arpanet mmc cit-20 0/54,arpanet cal-tech cit-vax 1/54,arpanet cit-11 acc 2/54,arpanet jpl-vax 3/54,arpanet anl 0/55,arpanet argonne anl-mcs 1/55,arpanet sumex-aim 0/56,arpanet aim su-dsn 1/56,arpanet tycho 0/57,arpanet nsa coins-gateway 1/57,arpanet coins nyu 0/58,arpanet bnl 1/58,arpanet brookhaven rutgers 2/58,arpanet rutgers-20 rutgers-10 etac 0/59,arpanet centacs-mmp 0/60,arpanet coradcom-tip 2/60,arpanet centacs-tf 3/60,arpanet stla-tac 2/61,arpanet stl-tip utexas-11 0/62,arpanet utexas-20 1/62,arpanet utexas bbn-rsm 0/63,arpanet bbnr bbn-tac 1/63,arpanet martin-b 1/64,arpanet mmc-b robins-tac 2/64,arpanet wralc-tac robins-unix 3/64,arpanet afsc-sd 0/65,arpanet afsd afsc-sd-tac 1/65,arpanet sd-tip aerospace 2/65,arpanet aero mitre-bedford 0/66,arpanet mitre-b afgl 1/66,arpanet afgl-tac 2/66,arpanet afsc-hq 0/67,arpanet hqafsc afsc-hq-tac 1/67,arpanet hqafsc-tac usgs1-multics 0/68,arpanet reston rest usgs1-amdahl 2/68,arpanet reston-amdahl ram usgs1-tac 3/68,arpanet usgs2-multics 0/69,arpanet denver usgs2-tac 1/69,arpanet usafa-gateway 2/69,arpanet usafa usgs3-multics 0/70,arpanet menlo usgs3-tac 1/70,arpanet bbn-clxx 2/71,arpanet clxx bbn-nu 0/72,arpanet bbn-unix 1/72,arpanet bbnu bbnp 2/72,arpanet sri-nic 0/73,arpanet nic sri-warf 1/73,arpanet warf tscf sri-ai 2/73,arpanet aic sri-iu 3/73,arpanet iuv wsmr-tip 2/74,arpanet ypg 0/75,arpanet yuma-tac 2/75,arpanet bbn-testip 2/76,arpanet mit-tac 2/77,arpanet ucb-arpa 0/78,arpanet ucb-c70 1/78,arpanet berkeley ucb ucb-ingres 2/78,arpanet ucb-vax ucb-ingvax mcclellan 3/78,arpanet sacramento-unix dec-2136 0/79,arpanet dec-marlboro 1/79,arpanet dec hi-multics 0/80,arpanet honey sac2-tac 1/80,arpanet sac-tac 2/80,arpanet nalcon 0/81,arpanet dtnsrdc 1/81,arpanet david-tac 2/81,arpanet nems 3/81,arpanet bbnt 0/82,arpanet bbn-vax 1/82,arpanet bbnv bbn-inoc 2/82,arpanet bbns 3/82,arpanet bbn-noc2 6/82,arpanet nswc-dl 0/84,arpanet nswc-tac 2/84,arpanet nwc-387a 0/85,arpanet nwc-elf 1/85,arpanet nwc-tac 2/85,arpanet nwc-387b 3/85,arpanet sandia 0/87,arpanet snl nlm-mcs 0/88,arpanet nlm mcs washington 0/91,arpanet udub udub-ward washington-tac 2/91,arpanet uw-vlsi 3/91,arpanet udub-vlsi nusc-npt 2/92,arpanet nusc 3/92,arpanet office-8 0/93,arpanet of8 office-10 1/93,arpanet darcom-ka office-12 2/93,arpanet csnet-sh 1/94,arpanet csnetb csnet uwisc wisconsin s1-gateway 0/95,arpanet s1-a 1/95,arpanet s1-c 3/95,arpanet udel-relay 0/96,arpanet ud-relay csnet-relay darcom-hq udel udel-tcp 1/96,arpanet udel-ee 2/96,arpanet cornell 3/96,arpanet

On Sat, May 7, 2022 at 10:23 AM ron minnich <rminnich(a)gmail.com> wrote: 10.2 is ambiguous. In a network context, it means, typically, 10.2.0.0/16 (though your mileage may vary). In a host context, it means 10.0.0.2. It's this confusion that has lead to many efforts to outright kill this notation. I know that it was around in the late 80s on TOPS-20 TCP/IP at Stanford, and in 4.2BSD (4.1c?). It may have also been in use at MIT. It's usage pre-dates my 1984 joining of the internet... Warner

curiouser and curiouser, at least some Go packages parse it that way: rminnich@a300:~/go/src/github.com/u-root/u-root/cmds/core/ping$ cpu -key ~/.ssh/cpu_rsa 192.168.16 date Sat May 7 12:56:29 PM PDT 2022 rminnich@a300:~/go/src/github.com/u-root/u-root/cmds/core/ping$ cpu -key ~/.ssh/cpu_rsa 192.168.0.16 date Sat May 7 12:57:05 PM PDT 2022 rminnich@a300:~/go/src/github.com/u-root/u-root/cmds/core/ping$ [cpu is basically ssh with the plan 9 cpu command baked in, written in Go] So as a convention, it's been out and about for close to 40 years, many systems honor it, it seems not many people know of it, and not everything interprets it the same way. Huh! Well, you learn something new every day. I found it a wonderful shorthand when somebody showed it to me, and it's wired into my fingers at this point. I just assumed everyone else used it too. I may dig around and try to figure out when Plan 9 picked it up, that might give me some idea as to provenance. On Sat, May 7, 2022 at 12:50 PM ron minnich <rminnich(a)gmail.com> wrote:

On Sat, May 7, 2022, 5:19 PM Bakul Shah <bakul(a)iitbombay.org> wrote: We just know the dotted quad world. In the early days of sparse addresses and crappy name service (or out of date host files) these shortcuts were a lifesaver. Warner

Hi Ron, It has been standardised; see inet_addr(3p) where ‘p’ means the POSIX version of the man page or https://pubs.opengroup.org/onlinepubs/9699919799/functions/inet_addr.html Briefly, the string must be one of a.b.c.d a.b.cd a.bcd abcd where the number of bytes represented is the number of characters. Each number is as defined by ISO C, e.g. ‘0x...’ means hex, thus ‘ping 017777777776’. That's all there is to it. It's simple to explain and I've used it for years too. Given POSIX defines it, without deprecation, programming languages which don't use the C library and programs which must parse the string themselves should follow POSIX to avoid those annoying programs which deviate from the long-established norm. Bug the ip(1) folks, pointing to POSIX. :-) -- Cheers, Ralph.

Ralph Corderoy wrote in <20220508102208.50A2822158(a)orac.inputplus.co.uk>uk>: |> 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. | |It has been standardised; see inet_addr(3p) where ‘p’ means the POSIX |version of the man page or |https://pubs.opengroup.org/onlinepubs/9699919799/functions/inet_addr.html | |Briefly, the string must be one of | | a.b.c.d | a.b.cd | a.bcd | abcd | |where the number of bytes represented is the number of characters. |Each number is as defined by ISO C, e.g. ‘0x...’ means hex, thus |‘ping 017777777776’. | |That's all there is to it. It's simple to explain and I've used it for |years too. Given POSIX defines it, without deprecation, programming |languages which don't use the C library and programs which must parse |the string themselves should follow POSIX to avoid those annoying |programs which deviate from the long-established norm. | |> 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. | |Bug the ip(1) folks, pointing to POSIX. :-) "However", RFC 2553 says RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999 The address conversion functions -- inet_ntoa() and inet_addr() -- convert IPv4 addresses between binary and printable form. These functions are quite specific to 32-bit IPv4 addresses. We have designed two analogous functions that convert both IPv4 and IPv6 addresses, and carry an address type parameter so that they can be extended to other protocol families as well. And for this POSIX says If the af argument of inet_pton( ) is AF_INET, the src string shall be in the standard IPv4 dotted-decimal form: ddd.ddd.ddd.ddd where "ddd" is a one to three digit decimal number between 0 and 255 (see inet_addr( )). The inet_pton() function does not accept other formats [.] I am too lazy / busy to check whether inet_pton() with AF_INET gets the short version right. (I personally had IPAdress:: .. pub boolean fromString(const char *_straddr, ui4 _straddrlen=M1::ui4): * Tries to parse the address as stored in \a _straddr. * If \a _straddr was successfully parsed a true boolean is returned. * Otherwise \THIS has not been modified. * * This function can parse all usual address representations, * in particular all of those which can be produced with toString(). * It can even parse "127. 0. 0. 1", "127.000.000.001", * but \e cannot parse "127. 0.0000. 1" (room for four digits). * And ditto for IPv6. * * \remarks If result is IPv6, flowInfo() and scopeId() are set to 0. * \note * ARPA strings are not understood! * I.e., strings produced by toArpaString() cannot be re-parsed to * a plain address with this one! * * \note * ::0.0.0.0 and ::FFFF:0.0.0.0 will fail. * ::0.0.0.1 and ::FFFF:0.0.0.1 will also fail. and now find the need to do /* xxx Client had this already, simply binary pass it, too? */ c_af = (su_cs_find_c(pgp->pg_ca, ':') != NIL) ? AF_INET6 : AF_INET; if(inet_pton(c_af, pgp->pg_ca, (c_af == AF_INET ? S(void*,&c_sip.v4) : S(void*,&c_sip.v6))) != 1){ su_log_write(su_LOG_CRIT, _("Cannot re-parse an already " "prepared IP address?: "), pgp->pg_ca); goto jleave0; } c_ip = (c_af == AF_INET) ? R(u32*,&c_sip.v4.s_addr) : R(u32*,c_sip.v6.s6_addr); quite lengthy and complicated. Of course inet_pton() can be made "extended to other protocol families", and maybe they are already even, but i find this distressing as either you need to provide some kind of _(un)?register() or even hardwire, maybe with a tree of #ifdef, those other families. And better watch out for EAFNOSUPPORT at runtime. Of course i came late and wanted / needed something specific so i am fine out. --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)