Odd TCP ECN related bahavior

[Jukka A. Ukkonen]

Hi all,

I am not on this mailing list. So, all responses should be sent
to my personal address.

I just noticed somewhat confusing network behavior when I was
using wireshark to understand why certain connections have been
unexpectedly slow.

My 11.3 stable (latest update 2019-06-23) seems to do this
according to wireshark...

.... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)

My system has this set, though...

net.inet.tcp.ecn.enable: 1

At the same time the peer system was reporting ECN capability...

.... ..10 = Explicit Congestion Notification: ECN-Capable Transport 
codepoint '10' (2)

Apparently increasing the value in...

net.inet.tcp.ecn.maxretries

doesn't help.

What should I make of this? Is the ECN implementation in 11.3 somehow
faulty or is this something more down to earth?


--jau