From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by finch.gentoo.org (Postfix) with ESMTPS id B8CC9138359 for ; Thu, 30 Jul 2020 12:48:12 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id DAEB5E0A9A; Thu, 30 Jul 2020 12:48:06 +0000 (UTC) Received: from smtp.hosts.co.uk (smtp.hosts.co.uk [85.233.160.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 98EB2E0A04 for ; Thu, 30 Jul 2020 12:48:06 +0000 (UTC) Received: from host86-157-100-178.range86-157.btcentralplus.com ([86.157.100.178] helo=[192.168.1.65]) by smtp.hosts.co.uk with esmtpa (Exim) (envelope-from ) id 1k17ye-0007Eb-EO for gentoo-user@lists.gentoo.org; Thu, 30 Jul 2020 13:48:04 +0100 Subject: Re: [gentoo-user] Local mail server To: gentoo-user@lists.gentoo.org References: <60f2cb96-0a2b-7701-6a8c-1f6646c64697@verizon.net> <5F213F71.4020402@youngman.org.uk> <16224a84-ac9f-360a-1e2d-dc04d57de307@verizon.net> From: antlists Message-ID: Date: Thu, 30 Jul 2020 13:48:05 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org X-Auto-Response-Suppress: DR, RN, NRN, OOF, AutoReply MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit X-Archives-Salt: 4d3b615f-7f4f-4e41-8d2c-8c88a21b1d91 X-Archives-Hash: ae7eac0650e9cf6ac3ba3dff7ea07a4c On 30/07/2020 12:13, Remco Rijnders wrote: > An IPv6 address is 128 bits in length. Usually an ISP allocates 64 > bits to a single customer, allowing the systems on/behind that > connection to automatically assign themselves an address based on > their MAC address for example. Note that also allocations bigger than > 64 bits are common so customers get 70 or 76 bits to use and can use > multiple subnets on their home/business networks. I don't think an ISP is supposed to allocate less ... As I understood it, the first 64 bits are the "network address", ie sort-of assigned to the edge router, and the remaining 64 bits are assigned by the network operator. So in your scenario of customers getting more bits, they are effectively being assigned 2^6 or 2^12 network addresses. Exactly the scenario planned for high-level ISPs parcelling out address space to low-level ISPs. And looking at the wikipedia page, it looks like the ISP *must* allocate at least a /64, because the spec says each device allocates itself a least-significant-64 address at random using a collision-detect protocol. Which is why many simplistic algorithms include the MAC address to (try to) guarantee a unique address on the first attempt. Cheers, Wol