For all cases where ping works in one direction but not in the opposite, you
are either pinging the board running u-Boot which does not respond to ICMP, or using an
invalid IP configuration or diagnostic tool. The standard ping
utility requires bidirectional communication to report a success. If you
ping successfully in one direction, the both directions are working. Everything
else is a result of either filtering, invalid configuration or improper
diagnostic tool.
Regarding what you called "router tests" it is especially unclear what was
the purpose of testing against a port marked as "down". Do you expect
Linux to forward a packet to a port that is disconnected from it's IP stack?
Anyway, I would suggest starting with checking that packet forwarding
is enabled:
cat /proc/sys/net/ipv4/ip_forward
and checking the ICMP errors returned by the board to the source of the test
traffic.
Best Regards,
Platon
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