Re: Increase tcp initial window

[John Hawkinson <jhawk%MIT.EDU@localhost>]

Loganaden Velvindron <loganaden%wolfman.devio.us@localhost> wrote on Sat,  6 
Apr 2013
at 06:09:06 -0400 in <20130406100906.GA3213%wolfman.devio.us@localhost>:

> What I propose is that we add it as a sysctl, similar to how OpenBSD does.

In principal this is fine, and I am much less concerned about it.
(though still a little concerned.) What IETF working group is dealing
with this stuff (tcpm?), and is anyone on this mailing list following it
closely? I'm not on the tcpm mailing list.

> rfc_3390 = 1 (default behaviour)
> rfc_3390 = 2 (draft-ietf-tcpm-initcwnd)
> 
> OR create a new sysctl
> initcwnd10 = 0 (default behaviour)
> initcwdnd1 = 1 (draft-ietf-tcpm-initcwnd)

It's not super-important, but I think we want an option with slightly
differnt properties. We want an option whose default value should
now be the initial window of 4, but whose default value can change
in the future when the IETF recommendation changes.

Therefore, I think we want a tri-state. The default being
to use window of 4 today, but to shift to using the window of 10
if the standards community changes to that. Then a value to
indicate always use 4, even if NetBSD's default changes in a future release
(so users can hard-code it to 4 now and into the future). And
a default value to indicate always use 10, even if NetBSD's default
changes in the future.

I guess probably I'd suggest

net.inet.tcp.initcwnd:
0       Choose initial window based on current IETF recommendations
        (now 4)
4       Force window to RFC3390 (Proposed Standard 2002) recommendation
10      Force window to draft-ietf-tcpm-initcwnd-08 (Experimental 2013)

All other values disallowed at this time. (But you could imagine
a afuture where the IETF recommended a value like 8 or 12, at which
point we could change the options).

On the other hand, it doesn't look like other implementors have chosen
an architecture like that.

--jhawk