Does TCP_FASTOPEN actually work?

[Michael Tuexen]

> On 5. Jul 2018, at 17:23, Pieter de Goeje <pieter at degoeje.nl> wrote:
> 
> I'm trying to test this new feature, but I have trouble getting the client to actually send a cached cookie. It keeps requesting new ones and as a consequence it never sends data in the initial SYN packet. Tcpdump shows that the server correctly replies to a cookie request with a cookie.
Can you provide a tracefile?
> 
> Or am I misunderstanding how it should work and is the cookie cache per-process instead of system wide?
No, the cache is system wide. You can use
https://reviews.freebsd.org/D14554
to see the entries.
> 
> I'm using the test programs from https://people.freebsd.org/~pkelsey/tfo-tools/ for this purpose.
How are you using the client and server?
> 
> Server and client run on r335760 or later, with no changes to net.inet.tcp.fastopen except that server_enable was set to 1.
Is client_enable = 1?
> 
> Related issue is that TCP_FASTOPEN is currently undocumented in tcp(4).
> 
> - Pieter
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