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 80D07C433C1 for ; Wed, 24 Mar 2021 07:14:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B203619EC for ; Wed, 24 Mar 2021 07:14:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231976AbhCXHNo (ORCPT ); Wed, 24 Mar 2021 03:13:44 -0400 Received: from 75-101-100-43.dsl.static.fusionbroadband.com ([75.101.100.43]:56058 "EHLO hop.toad.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235784AbhCXHNa (ORCPT ); Wed, 24 Mar 2021 03:13:30 -0400 X-Greylist: delayed 320 seconds by postgrey-1.27 at vger.kernel.org; Wed, 24 Mar 2021 03:13:30 EDT Received: from hop.toad.com (localhost [127.0.0.1]) by hop.toad.com (8.12.9/8.12.9) with ESMTP id 12O77bRl024496; Wed, 24 Mar 2021 00:07:37 -0700 To: Seth David Schoen cc: Florian Weimer , linux-man@vger.kernel.org, gnu@toad.com Subject: Re: [PATCH 1/1] ip.7: Add "special and reserved addresses" section In-reply-to: <20210322212944.GB10062@frotz.zork.net> References: <20210320002041.GZ2289@frotz.zork.net> <87ft0pzjtk.fsf@mid.deneb.enyo.de> <20210322175815.GX10062@frotz.zork.net> <20210322212944.GB10062@frotz.zork.net> Comments: In-reply-to Seth David Schoen message dated "Mon, 22 Mar 2021 14:29:44 -0700." Date: Wed, 24 Mar 2021 00:07:37 -0700 Message-ID: <24495.1616569657@hop.toad.com> From: John Gilmore Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org Perhaps the reason there is an interface for setting the broadcast address is so that it can be explicitly set to the lowest address (e.g. for compatability with 4.2BSD)? The ability to set an arbitrary broadcast address does seem rather useless otherwise. Sounds like a good email discussion to pull some historical info out of netdev participants and/or the Internet-History mailing list. Hmm -- after our patch, when the lowest address is no longer reserved for broadcast, you can still make the lowest address into a second broadcast address by setting it with ifconfig! That actually argues that our patch is even more innocuous; if anybody in the world actually needs the lowest address to be broadcast, they already have a userspace way to specify that. (By the way, the kernel code looks to me that if the interface broadcast address is set to 255.255.255.255 then it is NOT enabled, so only the default broadcast addresses are enabled. That doesn't seem to be documented either.) I don't know that the documentation that we added about how Linux support for reserved addresses varies from the RFCs needs to wait for these broadcast-related questions to be resolved. We can further improve that documentation once we know if and when "setting the broadcast address on an interface" has or used to have any usefulness. John