From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bifrost.lang.hm (mail.lang.hm [64.81.33.126]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 567BE21F29A; Mon, 2 Mar 2015 15:15:24 -0800 (PST) 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 t22NEwtw028191; Mon, 2 Mar 2015 15:14:58 -0800 Date: Mon, 2 Mar 2015 15:14:58 -0800 (PST) From: David Lang X-X-Sender: dlang@asgard.lang.hm To: Joe Touch In-Reply-To: <54F4DBC9.1010700@isi.edu> Message-ID: References: <7B3E53F5-2112-4A50-A777-B76F928CE8F2@trammell.ch> <54F4DBC9.1010700@isi.edu> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Brian Trammell , bloat , "cerowrt-devel@lists.bufferbloat.net" , "aqm@ietf.org" Subject: Re: [Cerowrt-devel] [aqm] ping loss "considered harmful" 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, 02 Mar 2015 23:15:53 -0000 On Mon, 2 Mar 2015, Joe Touch wrote: > On 3/2/2015 1:40 AM, Brian Trammell wrote: > ... >> The real solution is to create a utility called "ping" that uses >> traffic that gets prioritized the same way as the traffic you care >> about instead of ICMP echo request/reply. Users don't care about >> the packets on the wire so much as they do that you're supposed to >> ping things. > > There are three separate problems: > > 1. a ping that doesn't use ICMP > there are dozens of these > > 2. needing a reflector > ping gets around this only because the reflector is widely > deployed (and integrated into most OSes) > > 3. using the same port as the traffic you care about > transport protocol is only one problem (ICMP being a "transport > protocol" by virtue of using the IP protocol number field) > > the other is differential prioritization based on port number > > there's no easy solution to that; > every service would need an integrated > ping reflector > > I suspect #3 is the ultimate killer of this idea. The service you are trying to contact acts as a reflector for TCP traffic. If you send a syn you will get back a syn-ack from the TCP stack of the receiving system. For UDP systems, it gets more interesting and service specific. But for TCP systems it works today. David Lang