TCP Fast Open

Jeremy Harris jgh at
Thu Dec 5 15:25:29 UTC 2019


12.1 kernel with TCP_RFC7413
net.inet.tcp.fastopen.server_enable: 1
net.inet.tcp.fastopen.client_enable: 1

Using code copied from

I'm not seeing any TFO option on SYN.  This is on a loopback

Also, it appears to make no difference to the success of the
sendto whether or not TCP_FASTOPEN was set on the socket, adding to
the confusion.

What might I be doing wrong?

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