tested tcpdump on my router again with a working ping:
[root@bananapi ~]# tcpdump -nni eth0 icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
18:02:16.781003 IP 192.168.0.21 > 192.168.0.5: ICMP echo request, id 20647, seq 1, length 64
18:02:16.781234 IP 192.168.0.5 > 192.168.0.21: ICMP echo reply, id 20647, seq 1, length 64
18:02:17.781727 IP 192.168.0.21 > 192.168.0.5: ICMP echo request, id 20647, seq 2, length 64
18:02:17.781913 IP 192.168.0.5 > 192.168.0.21: ICMP echo reply, id 20647, seq 2, length 64
18:02:18.781675 IP 192.168.0.21 > 192.168.0.5: ICMP echo request, id 20647, seq 3, length 64
18:02:18.781869 IP 192.168.0.5 > 192.168.0.21: ICMP echo reply, id 20647, seq 3, length 64
18:02:19.781757 IP 192.168.0.21 > 192.168.0.5: ICMP echo request, id 20647, seq 4, length 64
18:02:19.781967 IP 192.168.0.5 > 192.168.0.21: ICMP echo reply, id 20647, seq 4, length 64
18:02:20.781712 IP 192.168.0.21 > 192.168.0.5: ICMP echo request, id 20647, seq 5, length 64
18:02:20.781912 IP 192.168.0.5 > 192.168.0.21: ICMP echo reply, id 20647, seq 5, length 64
as you can see with same command now there are outgoing icmp echo reply’s…so i assume that the problem is that the outgoing packets from gmac-kernel are getting damaged (truncated-ip - 6 bytes missing!) so my current router does not send a reply…
contacted John crispin (author from the patches on lede), hoping for a reply
added task to lede-project: https://bugs.lede-project.org/index.php?do=details&task_id=1403