Re: Low capped TCP network speeds over the Internet

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Mon, Mar 09, 2026 at 02:17:33AM -0300, z411 wrote:
> Good news again!
> 
> I managed to increase client->server scp speeds to the expected 8 MB/s
> by specifically increasing recvspace:
> 
> net.inet.tcp.recvspace=4194304
> 
> >From what I understand, the TCP window should've been growing
> automatically, and since my recvbuf_max is already 16MB, I didn't think
> recvspace would be the bottleneck. Apparently, that's not the case when
> SSH receives data?

ssh takes recvspace as the size of its own receive buffer, but it doesn't
understand autoscaling and is stuck at the initial size.

With HPN you can use the TcpRcvBuf option to set the initial receive
buffer size and with TcpRcvBufPoll=1 it tries to do its own kind
of autoscaling.


Greetings,
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."