Apple ECN, Bufferbloat, CoDel (fwd)

Mon Jun 15 16:36:40 UTC 2015

On Mon, Jun 15, 2015 at 9:13 AM, joel jaeggli <joelja at bogus.com> wrote:
> On 6/15/15 6:19 AM, Jared Mauch wrote:
>> On Sat, Jun 13, 2015 at 06:20:31PM +0200, Mikael Abrahamsson wrote:
>>>
>>> Hi,
>>>
>>> I just want to bring to your attention the below talk (I am too lazy to
>>> re-write the whole email for this slightly different audience).
>>>
>>> Takeaway:
>>>
>>> We'll see a lot of ECN enabled traffic in a few months. This shouldn't be a
>>> problem. I've been doing it to all my machines for 3-5 years without ill
>>> effects.
>
> you'll also find all the networks that use the entire tos field as part
> of the hash key... that's not exactly something you notice when you have
> a 1:1 host to ip correspondence unless it leads to reordering. but with
> stateless load balancing you can. fortunately those networks are
> observably rare.

I am aware of one such (very large) network that did, indeed, (and til
recently!) have devices that used the entire tos field in their ECMP
implementation. This led to re-ordering every time ECN "CE" was
exerted on ECN enabled flows. Testing for the existence of this
problem is not terribly hard (example, have a rule that periodically
exerts CE on a bunch of test tcp flows, count the reorders in
TCP_INFO), but the tools for it are kind of adhoc as yet.

I am curious if there is a SNMP mib/cacti/mrtg/other support for
reporting "CE" events in addition to loss?

Although fq_codel and pie (as deployed in linux - sadly docis-pie has
no ECN support in the spec) do do ecn markings (fq_codel *by
default*), deployment on bottleneck links is limited as yet. :)

My expectation is that this will make a difference first for apple
streaming video apps in the home, connecting to other devices in the
home (over wifi, ethernet, bluetooth, etc) that will start to make use
of this additional signalling information. And a billion new devices
with ecn on by default will probably expose all the other problems
rather rapidly. ;)

>>       I recall when ECN first came out and firewalls would block it causing me
>> issues on my Linux boxes sending list mail out.  It was a small enough percentage
>> that I mostly ignored it, but this will cause trouble for people who still
>> haven't fixed their broken firewalls.

Better fallbacks exist now.

>>       I encourage almost everyone on nanog to watch this talk.
>>
>>       - Jared
>>
>>> ---------- Forwarded message ----------
>>> Date: Sat, 13 Jun 2015 18:07:57 +0200 (CEST)
>>> From: Mikael Abrahamsson <swmike at swm.pp.se>
>>> To: bloat at lists.bufferbloat.net
>>> Subject: Apple ECN, Bufferbloat, CoDel
>>>
>>> I highly encourage people to take a look at:
>>>
>>> https://developer.apple.com/videos/wwdc/2015/?id=719
>>
>>> --
>>> Mikael Abrahamsson    email: swmike at swm.pp.se
>>
>
>

-- 
Dave Täht
What will it take to vastly improve wifi for everyone?
https://plus.google.com/u/0/explore/makewififast