On Sat, Dec 14, 2024 at 06:51:49PM +0000, Lloyd wrote: > I've a particularly vexing problem for which I've been unable to > identify the cause despite much research. > > There is an older Mac client on my network which experiences routine > packet loss when connected to OpenBSD boxes over SSH. This manifests > as the session "freezing" - text entered into a shell or text editor > is intermittently delayed by as much as 10-15s in some cases. It > occurs with such frequency the shell sessions become unusable. > > Initially I suspected a network issue. Packet captures on the client > side show many TCP retransmissions during the events. On the OpenBSD > side, these are identified as spurious retransmissions. I've checked > and fiddled with MTU, MSS, etc. to no avail. Examined routers, > switches, SSH settings. It does not matter if the client/server are on > the same or different VLANs. Multiple OpenBSD boxes are affected, > running on different hardware platforms, different hypervisors, etc. > > Now for the curve ball. I've a dozen Linux servers on this network and > none experience this issue at all. Furthermore, if I SSH into a Linux > box first, then SSH from there into the OpenBSD box, the issue goes > away. > > Any ideas where I should look next?
The mac client gets along with the linux server, but not with the openbsd server, so check for differences in the configuration of sshd on the openbsd server and on the linux servers (and I don't mean only the options explicitly set on sshd_config, the defaults might also be different). Also, the linux client plays nice with the openbsd server, but the mac client doesn't. As above, check for differences between the configuration of the mac client and the linux client. Starting both the server and the client with debug/verbose turned on might (e.g. "sshd -Dd" and "ssh -vv") might also give some hints, especially during the session freezes. > Regards > Lloyd > --
