Server/Client Alive mechanism issues

[Jeff Mitchell]

Hello,

I have a bandwidth-constrained connection that I'd like to run rsync
over through an SSH tunnel. I also want to detect any network drops
pretty rapidly.

On the servers I'm setting (via sshd_config):

ClientAliveCountMax 5
ClientAliveInterval 1
TCPKeepAlive no

and on the clients I'm setting (via ssh_config):

ServerAliveCountMax 5
ServerAliveInterval 1
TCPKeepAlive no

After about 5 seconds, the connection is being dropped, but during that
time the rsync is successfully transferring data near the full bandwidth
of the connection.

My understanding is that since the alive mechanism is running inside the
encrypted connection, OpenSSH would be able to (and would) prioritize
the alive packets over other data. So if any data is able to get through
(and it does) the alive packets should be able to as well. But this
doesn't seem to be the case.

Is my understanding of how this is supposed to work wrong? If not, could
I have a misconfiguration somewhere, or is it possible that this is some
old bug?  (This is OpenSSH_5.5p1 with OpenSSL 1.0.0a.)

Thanks,
Jeff