From nobody Sun Sep 12 15:25:56 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 B0DA117C6420 for ; Sun, 12 Sep 2021 15:26:04 +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 4H6tjl3qK6z3DPK for ; Sun, 12 Sep 2021 15:26:03 +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 18CFPuU5067615 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO) for ; Sun, 12 Sep 2021 10:25:56 -0500 (CDT) (envelope-from mike@mail.karels.net) Received: (from mike@localhost) by mail.karels.net (8.16.1/8.16.1/Submit) id 18CFPuZM067614; Sun, 12 Sep 2021 10:25:56 -0500 (CDT) (envelope-from mike) Message-Id: <202109121525.18CFPuZM067614@mail.karels.net> To: freebsd-net@freebsd.org From: Mike Karels Reply-to: karels@FreeBSD.org Subject: change to deprecate broadcast on host 0 of a subnet 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: <67612.1631460356.1@mail.karels.net> Date: Sun, 12 Sep 2021 10:25:56 -0500 X-Rspamd-Queue-Id: 4H6tjl3qK6z3DPK 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)[]; RCVD_COUNT_TWO(0.00)[2]; FREEFALL_USER(0.00)[mike]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; REPLYTO_ADDR_EQ_FROM(0.00)[]; PREVIOUSLY_DELIVERED(0.00)[freebsd-net@freebsd.org]; AUTH_NA(1.00)[]; RCPT_COUNT_ONE(0.00)[1]; TO_DN_NONE(0.00)[]; NEURAL_HAM_SHORT(-1.00)[-0.999]; DMARC_NA(0.00)[FreeBSD.org]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; 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]; TO_DOM_EQ_FROM_DOM(0.00)[] X-ThisMailContainsUnwantedMimeParts: N 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 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. Mike