Re: 60+% ping packet loss on Pi3 under -current and stable-13

Since about December of 2021 I've been noticing problems with
wired network connectivity on a pair of raspberry pi 3 machines
using wired network connections. One runs stable-13.1, the other
runs -current, both are up to date as of a few days ago.

Essentially both machines fail to respond to inbound network
connections via ssh or ping after reboot. If I get on the 
serial console and start an outbound ping to anywhere, both
machines respond to incoming pings with about a 65% packet
loss. Ssh connections are answered with delays of zero to
perhaps thirty seconds. Once connected ssh is usable but
erratic, with dropped characters, multi-second delays and
disconnects after random intervals from minutes to hours.

There are five other Raspberry Pi's on the network. Three
Pi2's run 12.3-stable, one Pi2 runs -current and a Pi4 runs
-current. All have no problems pinging one another and out
of network, so there's nothing obviously wrong with the net.
The network is not routed, but rather a block of eight
addresses simply bridged from my ISP over DSL.

It's been found that an image of 13.1-RC4 behaves similarly
on one Pi3 when on the public network but exhibits more normal
ping response when moved to a 192.168.1.n private network. On
the face of it, this seems significant, but I can't guess how.

I recall a post on one of the mailing lists about a bug that
caused problems when packets arrived out-of-order via NAT, 
but I'm using direct same-network pings and pinging through 
NAT seems little-to-no worse.

I was hoping to upgrade my stable-12 machines to stable-13,
but seeing this behavior gives me pause. If anyone can 
suggest tests or experiments to figure out what's going on
I'd be most grateful. I'm no programmer but can follow 
simple instructions. If this sounds like a known bug(s)
links to bugzilla would be of much interest.

Many thanks for reading, and any ideas! If some essential
details have been omitted please indicate and I'll try to
supply them. 

bob prohaska