Re: Strange ssh hangups, netbsd-9 GENERIC

[Jeffrey Walton <noloader%gmail.com@localhost>]

On Thu, Mar 18, 2021 at 2:49 PM Louis Guillaume <louis%zabrico.com@localhost> wrote:
>
> On 3/18/21 12:37 PM, RVP wrote:
> > On Thu, 18 Mar 2021, Louis Guillaume wrote:
> >
> >> Ok - i did something similar with "nc" and text files in /var/log. It
> >> is able to connect and transfer up to and no more that 6144 bytes
> >> before closing. This seems to be consistent with what I was seeing via
> >> ssh.
> >>
> >> Smaller files transfer completely, but anything larger than 6144b is
> >> truncated at exactly 6144b == 6k.
> >>
> >> After some reading, that seems to smell like some kind of MTU or maybe
> >> jumbo frame business. All systems here on on gigabit ethernet. Just a
> >> hunch. Maybe it's my switch.
> >>
> >
> > Try turning jumbo frames off--you don't really need it. Reboot the switch
> > also.
> >
> >> I can't rule out the firewall (ipfilter) - but even if that is the
> >> cause, this would be unexpected behavior.
> >>
> >
> > Try a port (both on nc(1) and sshd) other than 22.
> >
> > -RVP
>
> Hrmpf - looks like jumbo frames are already off...
>
> wm1: flags=0x8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>
> ... also a tcpdump shows the largest packet size being 1500, so that all
> seems in order. It does show the sshd sending an unexpected "RST" packet
> right before the end, though...
>
>      192.168.1.2.22 > 192.168.1.126.64517: Flags [R], cksum 0xbd47
>
> ... which leads me to think it's something with sshd now.

Before you go too far down a rabbit hole, you may want to swap-in a
new cat6 cable.

Jeff