Subject: [tcpm] Fwd: Probing the viability of TCP extensions

From: Lars Eggert <[email-masked]>
Date: Tue, 22 Jun 2010 22:52:24 +0300

Thanks for the link, Hannes!

Begin forwarded message:
> From: "Tschofenig, Hannes (NSN - FI/Espoo)" <[email-masked]>
> Date: June 22, 2010 22:45:28 GMT+03:00
> To: "Eggert Lars (Nokia-NRC/Espoo)" <[email-masked]>
> Subject: Probing the viability of TCP extensions
> 
> FYI: http://www.imperialviolet.org/binary/ecntest.pdf 
>

---

From: "Scheffenegger, Richard" <[email-masked]>
Date: Wed, 23 Jun 2010 00:13:58 +0100

Adam is a member of the TCPM list :)

I am curious, out of the 1,07% of Hosts where ECN negotiation was
successful, is there any indication that internet routers are actually
making use of the ECT / CE codepoints in the IP header?

Ie. When loading a page from those web servers, were any CE marked
segments received?

Or is ECN only negotiated between hosts, but never actually used to
deliver a benefit (which might explain the extremely low adoption rate
almost 10 years after standardization.

Also, your research was done in 2008 - Microsoft has introduced ECN
support with Windows Vista / 7, is there any indication of rising levels
of public ECN support, or still a falling trend?

I'm asking as there seems to be renewed interest in having
ECN-singalling in private networks again...

Best regards,

Richard Scheffenegger

> -----Original Message-----
> From: Lars Eggert [mailto:[email-masked]] 
> Sent: Dienstag, 22. Juni 2010 21:52
> To: Multipath TCP Mailing List; [email-masked] Extensions
> Cc: Hannes Tschofenig
> Subject: [tcpm] Fwd: Probing the viability of TCP extensions
>

---

From: Adam Langley <[email-masked]>
Date: Tue, 22 Jun 2010 21:11:10 -0400

> Adam is a member of the TCPM list :)

Er, yea, hi :)

> making use of the ECT / CE codepoints in the IP header?

I didn't look for it. The prober didn't progress beyond the initial
TCP handshake.

> ECN-singalling in private networks again...

I haven't retried the experiment since the initial investigation.
However, there wasn't anything special about it: I did it from a
standard hosting company VPS machine (after clearing it with them
first). The only sensitive bit was the list of hostname from the
Google index. You could just download the .com zone and achieve much
the same effect I'm sure.

AGL

-- 
Adam Langley [email-masked] http://www.imperialviolet.org

---

From: Patrick McManus <[email-masked]>
Date: Mon, 28 Jun 2010 11:31:02 -0400

> making use of the ECT / CE codepoints in the IP header?

I have a blog post from 2007 on a different, much smaller, data set:

http://bitsup.blogspot.com/2007/08/lamenting-ecn-deployments.html

Basically, it looks at a small sample of 41K flows from my home network
and sees 8% of them negotiated ECN end to end (which certainly skews
high), but doesn't see a single instance of a packet being marked by a
router.

just one data point.

---

From: Fred Baker <[email-masked]>
Date: Tue, 29 Jun 2010 11:29:08 -0700

how many routers does it show that had ECN marking configured active?

On Jun 28, 2010, at 8:31 AM, Patrick McManus wrote:

> _______________________________________________
> multipathtcp mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/multipathtcp

http://www.ipinc.net/IPv4.GIF

---

From: Patrick McManus <[email-masked]>
Date: Tue, 29 Jun 2010 19:04:39 -0400

> how many routers does it show that had ECN marking configured active?

not a single ecn capable flow in the data contained a ecn-marked packet.
This was general Internet traffic, including a lot of spam SMTP flows
from abroad that you would think would have a reasonable chance of
seeing congestion.

I don't see how to identify which if any routers had ecn configured on,
but the implication is that it is very few if any. (or that there is no
congestion on "my" internet :)), right?

---

From: Hagen Paul Pfeifer <[email-masked]>
Date: Wed, 30 Jun 2010 02:04:59 +0200

>congestion on "my" internet :)), right?

;-) was this insight surprising? ECN lacks one important attribute: it is not
good-natured if things goes wrong. What would you do if you had to configure a
core router: a) configure the router and setup standard RED/WRED where you
_know_ that if you are on fire and drop packets the sender will reduce their
sending rate or b) configure ECN and _hope_ that everything between you, the
receiver the last but not least the sender goes right?

Eventually you will think about the advantages of ECN and the reduced
TCP/DCCP/whatever retransmissions but is this more important then the former
paragraph? I don't think that this is the view of the guys at the core
routers.

ECN is a technical superior answer for a question questioned in a complex and
fragile environment.

HGN

PS: anyway, nice analysis! ;)

-- 
Hagen Paul Pfeifer <[email-masked]>  ||  http://blog.jauu.net/
Telephone: +49 174 5455209           ||  Key Id: 0x98350C22
Key Fingerprint: 490F 557B 6C48 6D7E 5706 2EA2 4A22 8D45 9835 0C22