From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from chi.subsignal.org (cxd-2-pt.tunnel.tserv11.ams1.ipv6.he.net [IPv6:2001:470:1f14:ed::2]) by huchra.bufferbloat.net (Postfix) with ESMTP id CCA9421F12A for ; Mon, 10 Dec 2012 03:27:03 -0800 (PST) Received: from [192.168.178.21] (unknown [212.255.243.50]) by chi.subsignal.org (Postfix) with ESMTPSA id E0C191260DF; Mon, 10 Dec 2012 12:27:22 +0100 (CET) Message-ID: <50C5C705.3060108@openwrt.org> Date: Mon, 10 Dec 2012 12:27:01 +0100 From: Steven Barth User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Dave Taht References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Mailman-Approved-At: Mon, 10 Dec 2012 12:58:58 -0800 Cc: cerowrt-devel@lists.bufferbloat.net Subject: Re: [Cerowrt-devel] Current state of ipv6 in openwrt barrier breaker X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 10 Dec 2012 11:27:04 -0000 On 10.12.2012 10:15, Dave Taht wrote: >> * Prefixes are automatically split up and distributed over >> downstream-interfaces OR by choice mapped to an ULA-address (NPT66). > > Hmm. The homenet folk have a prefix assignment and router discovery > process defined in their PD over ospf (somewhat crazy) > implementation... > > My expectation here is that ISPs are going to be parsimonious in > handing out anything bigger than a /64, certainly anything bigger than > a /56 is going to be scarce. So I'd hope that address assignment using > NPT66 would start with the bottom addresses and work up. cerowrt would run into problems if the ISPs would only assign a single /64. Even NPT would not help here as two distinct ULA /64 could not be mapped to the same public /64 without the possibility of collisions. So it might be necessary to relay between the downstream interfaces in this case so that they share a /64 or did you have something else in mind? However I guess and from what I have seen most ISP will probably assign a /56 or at least a /60. For OpenWrt a /64 would not so problematic as there is - by default - only 1 (bridged) lan-interface so a single /64 is sufficient for most users. This is how the prefix distribution works either for the ULA or the public prefixes. I've implemented this straight forward not looking at any specification as the local prefix distribution should not be mandated imo by any RFC. * For ULA fd00::/48, the first /64 would be fd00::/64, the 2nd fd00:0:0:1::/64 etc. * Padding (unused adress-space) is added if the alignment cannot be satisfied (e.g. one interface wants a /64, the second a /62, then there will be a padding or 1 /64 and 1 /63 in between). * If a downstream-interface goes down, its assigned prefix is preserved in case it later comes up again. * Assignments for a public prefixes are forgotten once the prefix is removed (e.g. wan goes down). In the current implementation the NPT will map the public prefix to the lower part of the ULA, meaning a public /56-prefix will be mapped onto fd00::/56 if the ULA is fd00::/48 and everything outside this /56 would not be mapped so care has to be taken. This is a bit unpredictable - I know - but in the end we cannot know what size the public prefix from the ISP will be and I guess if there are only a few /64-downstream interfaces it is unlikely to clash for a majority of users. > > Somewhat related to that, is the concept of actually USING ipv6 for a > few things that it's good at. For example, a much greater randomized > port space can be gained if the dns server is the only daemon > listening on a dedicated ipv6 address (like a ::3) I'm currently wondering if it would make sense to implement a randomization strategy in case we have e.g. a /56 prefix and only want to assign one or two /64 so that the /64 would not always be ...1::/64 and 2::/64 but it would be a bit complicated with the dynamic prefix assignment of downstream-interfaces and especially when it comes to ULA and us not knowing before-hand what length the public prefix will be.