From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EE8AC433C1 for ; Sat, 20 Mar 2021 19:50:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BD1561928 for ; Sat, 20 Mar 2021 19:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229618AbhCTTuP (ORCPT ); Sat, 20 Mar 2021 15:50:15 -0400 Received: from albireo.enyo.de ([37.24.231.21]:46452 "EHLO albireo.enyo.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229826AbhCTTuD (ORCPT ); Sat, 20 Mar 2021 15:50:03 -0400 Received: from [172.17.203.2] (port=50453 helo=deneb.enyo.de) by albireo.enyo.de ([172.17.140.2]) with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) id 1lNhbk-0007pO-1n; Sat, 20 Mar 2021 19:50:00 +0000 Received: from fw by deneb.enyo.de with local (Exim 4.92) (envelope-from ) id 1lNhbj-0003SH-W8; Sat, 20 Mar 2021 20:50:00 +0100 From: Florian Weimer To: Seth David Schoen Cc: linux-man@vger.kernel.org, gnu@toad.com Subject: Re: [PATCH 1/1] ip.7: Add "special and reserved addresses" section References: <20210320002041.GZ2289@frotz.zork.net> Date: Sat, 20 Mar 2021 20:49:59 +0100 In-Reply-To: <20210320002041.GZ2289@frotz.zork.net> (Seth David Schoen's message of "Fri, 19 Mar 2021 17:20:41 -0700") Message-ID: <87ft0pzjtk.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org * Seth David Schoen: > +On any locally-attached IP subnet, the lowest-numbered address and > +highest-numbered address (e.g., the .0 and .255 addresses on a subnet > +with netmask 255.255.255.0) are both designated as broadcast addresses. > +These cannot usefully be assigned to an interface, and can only be > +addressed with a socket on which the > +.B SO_BROADCAST > +option has been explicitly enabled. I think the broadcast address is actually settable to some degree, and /31 subnets do not have them. I wouldn't be surprised if kernel behavior also depended on the network device.