[Bloat] enabling outgoing tcp-ecn by default for ipv6 links

[Hannes Frederic Sowa]

On Thu, Dec 27, 2012 at 12:10:35PM -0800, Rick Jones wrote:
> On 12/26/2012 06:37 PM, Hannes Frederic Sowa wrote:
> >I am thinking about advancing the ipv4/tcp_ecn knob in linux to
> >distinguish between ipv4 and ipv6 transport and enable ecn signaling
> >on outgoing ipv6 connections by default (for me, at least). I am
> >currently doing so with the help of iptables (echo 1 > tcp_ecn and -j
> >ECN --ecn-tcp-remove).
> 
> Any particular reason you aren't willing/able to just flip the 
> net.ipv4.tcp_ecn sysctl to turn it on for both?  FWIW, that is what I 
> have done on netperf.org, with an eye towards seeing what ceases 
> working.  Thusfar things seem OK.  At least I've not had anyone contact 
> me to say "Hey! Why can't I reach netperf.org!" ...

But ecn is not employed as long as your clients won't signal ecn
support, too. So there is nothing to break.

I have a squid server where I actually needed to disable outgoing ecn
support because of reachability problems to a german university last
year. This seems to be fixed this year (and they have enabled ipv6,
thus supporting my assumption :) ). I suppose there are still many
ecn-blackholes rendering enabling ecn by default unlikely. I am a bit
more confident this could work some day for ipv6.

Greetings,

  Hannes