Re: [aqm] ping loss "considered harmful"

Joe Touch <touch@isi.edu> Mon, 02 March 2015 23:26 UTC

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Date: Mon, 02 Mar 2015 15:25:26 -0800
From: Joe Touch <touch@isi.edu>
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Cc: Brian Trammell <ietf@trammell.ch>, bloat <bloat@lists.bufferbloat.net>, Dave Taht <dave.taht@gmail.com>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] ping loss "considered harmful"
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On 3/2/2015 3:14 PM, David Lang wrote:
> 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.

Sure, but SYNs and SYN-ACKs don't get prioritized the same as
non-control TCP segments. And they could have been spoofed by a middlebox.

Joe