From: Daniel Borkmann <dborkman@redhat•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: Florian Westphal <fw@strlen•de>,
David Miller <davem@davemloft•net>,
netdev@vger•kernel.org
Subject: Re: [PATCH -next 0/2] net: allow setting ecn via routing table
Date: Fri, 31 Oct 2014 10:24:05 +0100 [thread overview]
Message-ID: <54535535.3040900@redhat.com> (raw)
In-Reply-To: <1414710342.15352.14.camel@edumazet-glaptop2.roam.corp.google.com>
On 10/31/2014 12:05 AM, Eric Dumazet wrote:
> On Thu, 2014-10-30 at 23:15 +0100, Florian Westphal wrote:
>
>> Do you think a fallback to non-ecn for retransmitted syns would help?
>> If not, do you think having ecn tunable available via route is helpful?
>
> Unfortunately some firewalls are buggy and accept a single SYN per flow.
>
> You would need to blacklist ecn at first sign of a possible ecn problem,
> for all following connections attempts.
>
> Note that ECN problems are not only contained in SYN packets being
> eventually dropped. You might have a success to establish a flow, and
> later get CE marks for all packets and cwnd converges to 1.
Wow, that is buggy! Btw, fwiw, there was a recent study [1] (paper
not public yet) which scanned the Alexa's publicly available top
million websites list from a vantage point in US, Europe and Asia:
Half of the Alexa list will now happily use ECN (tcp_ecn=2, most
likely blamed to commit 255cac91c3c9 ;)), the break in connectivity
on-path was found is about 1 in 10,000 cases. Timeouts rather than
receiving back RSTs were much more common in the negotiation phase
(and mostly seen in the Alexa middle band, ranks around 50k-150k):
from 12-thousand hosts on which there _may_ be ECN-linked connection
failures, only 79 failed with RST when _not_ failing with RST when
ECN is not requested.
It's unclear though, how much equipment actually marks the CE, and
as you mention above, marks it correctly ...
> This is really a lot of work to get all sorted out.
Yep, you are right.
[1] http://ecn.ethz.ch/
prev parent reply other threads:[~2014-10-31 9:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-25 22:38 [PATCH -next 0/2] net: allow setting ecn via routing table Florian Westphal
2014-10-25 22:38 ` [PATCH -next 1/2] syncookies: remove ecn_ok validation when decoding option timestamp Florian Westphal
2014-10-25 22:38 ` [PATCH -next 2/2] net: allow setting ecn via routing table Florian Westphal
2014-10-28 20:57 ` [PATCH -next 0/2] " David Miller
2014-10-29 12:23 ` Florian Westphal
2014-10-30 19:59 ` David Miller
2014-10-30 20:52 ` Florian Westphal
2014-10-30 21:07 ` Eric Dumazet
2014-10-30 22:15 ` Florian Westphal
2014-10-30 23:05 ` Eric Dumazet
2014-10-30 23:16 ` Florian Westphal
2014-10-30 23:30 ` Eric Dumazet
2014-10-31 3:49 ` David Miller
2014-10-31 9:24 ` Daniel Borkmann [this message]
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