Mikael Abrahamsson swmike at
Fri Nov 7 07:27:58 UTC 2008


On LKML (Linux Kernel Mailing List) there is talk 
<> about shipping the Linux kernel with 
ECN turned on by default (it was on by default a few years back but that 
change was reverted due to too many sites dropping ECN enabled SYNs).

Recent investigations <> 
shows that 0.5% of end hosts will drop SYN packets with ECN turned on. 
This is approximately the same rate I have seen for A/AAAA adoption in 
this tread <>.

Do we in the operational ISP community have an opinion on ECN adoption 
that we want to voice? As far as I can discern from 
for ECN to actually be useful, we (the ISPs) have to turn this option on 
in the routers as well. Is anyone doing this today? What vendors support 

When I thought about it, the IP core (10G links etc) first came to mind, 
and there it's fairly easy to roll out (since I guess a lot of us do WRED 
already), but what about on slower links? Would it make sense to have our 
DSLAMs do this? What about DSL/cable modems (well, vendors should first 
realise that FIFO is not great to begin with :P) ?

<> is a summary page I found on ECN that looks 
like a good resource for further reading. Is anyone looking into including 
ECN configuration into some BCP document?

Mikael Abrahamsson    email: swmike at

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