Erratic ping behavior, was Re: Pi3 answers ssh only if outbound ping is running on -current

[changed subject to more clearly reflect the symptoms]

On Mon, Feb 14, 2022 at 09:59:23PM -0800, Mark Millard wrote:
> >>>> Since I have a context working based on the kernel in:
> >>>> 
> >>>> https://artifact.ci.freebsd.org/snapshot/stable-13/371633ece3ae88e3b3d7a028c372d4ac4f72b503/arm64/aarch64/kernel.txz
> >>>> 
> >>>> I recommend that you try that exact same kernel in your
> >>>> stable/13 context. I recommend renaming the existing
> >>>> /boot/kernel before expanding the kernel.txz into / and
> >>>> so causing a new /boot/kernel/ to be filled in.
> 

It looks like the kernel isn't an obvious culprit: Versions
from late October to a few days ago all behave the same way.

Even when booted single-user, with the ue0 device brought up
by hand, only about 1% of incoming pings are answered. That
figure rises to a little over 50% when there's an outgoing ping
process (both running a 1/seccond). Destination of the ping
does not seem to matter, an unused IP seems to work fine. 

AIUI, nothing of userland apart from a shell and the ping
process will be running under those circumstances. Is this
correct? 

Might the trouble be inherited from the boot files? I've left
them alone since the machine does boot and updating them 
isn't automated. Right now the machine boots from microSD
and then runs bootcmd_usb0.

One oddity noticed during the kernel-swapping experiments
is that at the loader prompt some kernel names don't seem
to be recognized. If I type kernel or kernel.old it's
loaded immediately. If I type kernel.no-bpf which is one
I built, booted using the name kernel and then saved with
the name kernel.no-bpf it can't be found, even though it's
visible via ls at the OK prompt. Might - be a prohibited
or priviledged character to the loader? Names like
kernel.20220214 are likewise not recognized, even though
they're visible using ls.

For lack of immediately better ideas I've started stress2
running in single-user mode to see if anything of interest
results.

Thanks for reading, and any ideas!

bob prohaska