From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bifrost.lang.hm (lang.hm [66.167.227.134]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 24FE73B25E for ; Fri, 6 May 2016 15:54:35 -0400 (EDT) Received: from asgard.lang.hm (asgard.lang.hm [10.0.0.100]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id u46JsVsX016044; Fri, 6 May 2016 12:54:31 -0700 Date: Fri, 6 May 2016 12:54:31 -0700 (PDT) From: David Lang X-X-Sender: dlang@asgard.lang.hm To: Jonathan Morton cc: Stephen Hemminger , cake@lists.bufferbloat.net In-Reply-To: <89951A22-6568-4A07-BC52-5142DADB95BC@gmail.com> Message-ID: References: <1462205669.5535.254.camel@edumazet-glaptop3.roam.corp.google.com> <2D83E4F6-03DD-4421-AAE0-DD3C6A8AFCE0@gmail.com> <1577AB06-3C14-43D1-92AD-E37CEDCB8E11@gmail.com> <8F329CCB-038C-4EF4-A01D-DB8C093AE6B2@gmx.de> <20160506083114.0730d9f1@xeon-e3> <26BC8860-0485-4052-A8AC-574737B878E6@gmail.com> <89951A22-6568-4A07-BC52-5142DADB95BC@gmail.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="680960-2070786906-1462564471=:1768" Subject: Re: [Cake] Fwd: [Codel] fq_codel_drop vs a udp flood X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 06 May 2016 19:54:35 -0000 This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --680960-2070786906-1462564471=:1768 Content-Type: TEXT/PLAIN; charset=utf-8; format=flowed Content-Transfer-Encoding: 8BIT On Fri, 6 May 2016, Jonathan Morton wrote: >> On 6 May, 2016, at 22:14, David Lang wrote: >> >> On Fri, 6 May 2016, Jonathan Morton wrote: >> >>>> On 6 May, 2016, at 21:50, David Lang wrote: >>>> >>>> what IP id are you referring to? I don't remember any such field in the packet header. >>> >>> It’s the third halfword. >> >> half a word is hardly enough to be unique across the Internet, anything that small would lead to lots of attackes that inserted garbage data into threads. > > It doesn’t need to be globally unique. It merely identifies, in conjunction with src/dst address pair (so 80 bits in total), a particular sequence of fragments to be reassembled into the original packet. If the fourth halfword is zero (or has only the Don’t Fragment bit set), the IP ID field has no meaning. Hence the entire second word can be considered fragmentation related. > > I agree that it’s not a very robust mechanism; it breaks under extensive packet reordering at high packet rates (circumstances which are probably showing up in iperf tests against flow-isolating AQMs). It would be better not to have fragmentation at the IP layer at all. But it’s not as bad as you say; it does work for low packet rates, which is all it was intended for. > > Here’s my preferred reference diagram: https://nmap.org/book/tcpip-ref.html rfc-6864 shows that this field is not used the way you think it is in practice (if it was, nobody would have been able to exceed 6.4Mbps) Given all the things that can cause fragmentation on virtually every packet (tunnels/vpns), and the fact that having this be unique would restrict all traffice between a given source and destination to 6.4Mbps, I am extremely doubtful that it is used the way that rfc-6864 suggests (after all it's a recent RFC, 2013) I know that I've looked at packet dumps that have shown fragmented data and seen the port numbers in the fragment headers. I'd bet that in practice firewalls/etc ignore the IP ID field. David Lang --680960-2070786906-1462564471=:1768--