Explicit Congestion Notification (ECN, RFC 3168) has been around for quite a while now, but there are still lots of devices and hosts out there that don’t support it properly. For instance,, and apparently all HP’s ILO and ILO2 baseboard management systems.

If you’re on a GNU/Linux system, just try it:

echo 0×1 > /proc/sys/net/ipv4/tcp_ecn

Now you can’t go to NPR’s website.

echo 0×0 > /proc/sys/net/ipv4/tcp_ecn

And now you can. If you compile your own kernels, you might have noticed that ECN is on by default these days. I can’t seem to find the configuration option to disable it anymore in the latest 2.6.20rc kernels, but the proc interface is still there.

I’ve left a message on NPR’s tech support page, let’s see if they fix this. As for HP’s ILO’s, maybe I can ask an acquaintance to forward this bug report to the right group/person…

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3 Responses to ECN

  1. ward says:

    Turns out that NPR listens. I got a response to my query, which stated that they are aware of the problem and are working to resolve it.

    Yay NPR! Good work.

  2. ward says:

    Thanks Ben! Indeed, it works now. I really appreciate how NPR listens to its listeners :)

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