From nobody Wed Sep 15 23:18:02 2021 X-Original-To: freebsd-net@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 8E65F17C407B for ; Wed, 15 Sep 2021 23:18:10 +0000 (UTC) (envelope-from mike@mail.karels.net) Received: from mail.karels.net (mail.karels.net [216.160.39.52]) by mx1.freebsd.org (Postfix) with ESMTP id 4H8x352kjVz3Hx7 for ; Wed, 15 Sep 2021 23:18:09 +0000 (UTC) (envelope-from mike@mail.karels.net) Received: from mail.karels.net (localhost [127.0.0.1]) by mail.karels.net (8.16.1/8.16.1) with ESMTPS id 18FNI3kg082608 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Wed, 15 Sep 2021 18:18:03 -0500 (CDT) (envelope-from mike@mail.karels.net) Received: (from mike@localhost) by mail.karels.net (8.16.1/8.16.1/Submit) id 18FNI24k082607; Wed, 15 Sep 2021 18:18:02 -0500 (CDT) (envelope-from mike) Message-Id: <202109152318.18FNI24k082607@mail.karels.net> To: "Bjoern A. Zeeb" cc: freebsd-net@freebsd.org From: Mike Karels Reply-to: karels@freebsd.org Subject: Re: change to deprecate broadcast on host 0 of a subnet In-reply-to: Your message of Wed, 15 Sep 2021 15:57:34 -0000. List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <82605.1631747882.1@mail.karels.net> Date: Wed, 15 Sep 2021 18:18:02 -0500 X-Rspamd-Queue-Id: 4H8x352kjVz3Hx7 X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=none (mx1.freebsd.org: domain of mike@mail.karels.net has no SPF policy when checking 216.160.39.52) smtp.mailfrom=mike@mail.karels.net X-Spamd-Result: default: False [-1.70 / 15.00]; HAS_REPLYTO(0.00)[karels@freebsd.org]; ARC_NA(0.00)[]; FREEFALL_USER(0.00)[mike]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; REPLYTO_ADDR_EQ_FROM(0.00)[]; DMARC_NA(0.00)[freebsd.org]; AUTH_NA(1.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; NEURAL_HAM_SHORT(-1.00)[-1.000]; RCPT_COUNT_TWO(0.00)[2]; R_SPF_NA(0.00)[no SPF record]; FORGED_SENDER(0.30)[karels@freebsd.org,mike@mail.karels.net]; RCVD_NO_TLS_LAST(0.10)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:209, ipnet:216.160.36.0/22, country:US]; FROM_NEQ_ENVFROM(0.00)[karels@freebsd.org,mike@mail.karels.net]; RCVD_COUNT_TWO(0.00)[2] X-ThisMailContainsUnwantedMimeParts: N Bjoern wrote: > On 12 Sep 2021, at 15:25, Mike Karels wrote: > > Long ago (4.2BSD), the IP broadcast address was the lowest address on > > a > > network, the one with a host part of 0. In RFC1122, the broadcast > > address > > was standardized using a host part of all ones. 4.3BSD changed its > > default, and made the broadcast address settable with ifconfig. > > However, > > FreeBSD *still* broadcasts packets sent to the lowest address on a > > subnet. > > > > I have a change in review to stop broadcasting the lowest address on a > > subnet by default, but added a sysctl to revert to the current > > behavior. > > I really doubt that anyone is still using a 0-based broadcast address. > > This change allows host 0 on a subnet to be used as an assigned host > > address, as long as the systems on that network support it (including > > routers). Linux already has this change. > > > > The review is https://reviews.freebsd.org/D31861. See also > > https:/datatracker.ietf.org/draft-schoen-intarea-lowest-address/ and > I think it is: > https://datatracker.ietf.org/doc/draft-schoen-intarea-lowest-address/ Thanks for the correction, I think I had to type this rather than pasting. > > some of the discussion in https://reviews.freebsd.org/D19316. > > > > Comments are welcome on the review. I will wait a couple of days > > for comments before proceeding. I am also interested in comments on > > whether this should be MFC'ed to 13-stable after a suitable delay. > I would have even gone one further step back and put this under > EXPERIMENTAL > in HEAD and wait until this draft has gone anywhere but with your sysctl > I think > it is fine (from reading the email not the recent review). > I would prefer if the current behaviour stayed default (would also MFC > better) > and then flip if this will indeed go anywhere. I considered that, but I think that the current behavior is simply wrong. We broadcast packets to the lowest address on the net, but we don't receive these broadcasts as such. I was surprised to find that we were still broadcasting these packets. I can't think of any reason we should do that. Any other opinions on the default setting of the sysctl? > My personal note on this is: it is riding a dead horse, driven by > economics, > and it feels 30 year too late to still do this and change this historic > behaviour. 30 years ago, one might have been able to find a Vax running 4.2BSD to send these packets to. I agree that this change should have been made earlier, but that's not a good reason not to do it now. Whether or not the change has economic benefit, it may allow people to use an additional host on small networks. But I look at this primarily as a cleanup. Mike