Now I've tried to debug the UDP traffic using tcpdump when synscan pro is trying to connect:
mount = PC-direct
app = TABLET, no broadcast
# tcpdump -s 0 host TABLET and udp
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on wlp2s0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
19:19:39.240388 IP TABLET.45560 > SERVER.11880: UDP, length 4
19:19:39.290710 IP SERVER.11880 > TABLET.45560: UDP, length 1
19:19:39.304042 IP SERVER.11880 > TABLET.45560: UDP, length 7
write - 2024/03/05 19:19:39 OPEN (ipv6,::ffff:TABLET,45560)
:e1
read - 2024/03/05 19:19:39 OPEN (ipv6,::ffff:TABLET,45560)
=020402
To me this looks fine - my TABLET sends from synscan app ":e1\r" and my mount answers with "=020402\r". But synscan app still cannot connect.
That's a good looking sample. But I've also seen tests where the app is sending its message three times within one UDP packet like ":e1\r:e1\r:e1\r" - and my mount also answers 3 times within one reply packet. Sometimes my mount seems to give up and starts to reply with its coordinates.
Hope that someone here might have an idea ...
Regards, Michael
Some additional mystery:
From the above tcpdump I'd conclude that communication is using ipv6. If I enforce ipv4 (by adding "ipv4," in front of 118800 within ser2net.yaml) my mount now reflects back ":e1" for each connect request from synscan app.