Client only connect when hint added

Hi, I am running urbackup in docker. The client always offline unless I put their ip in discovery hint. The server and client are in the same subnet 192.168.1.x. Does anyone have idea:

  1. Why the broadcast cannot work between server and client under same subnet?
  2. If the broadcast not working, can I add a range /list of ip into the discovery hint instead of enter 1 by 1? Otherwise, I have to check and add each client ip and rework again if DHCP assign a new IP…
  3. Can discovery hint work on different subnet 192.168.1.xx vs 192.168.3.xx? I cannot make client online no matter via internet mode or not.