+-----------------------------------------------------------------------
| Running jdk-21 on OpenBSD
+-----------------------------------------------------------------------

ipv4 and v6 networking
======================
  ipv4 to ipv6 address mapping is disabled on OpenBSD. This means the
  jdk can only use ipv4 addresses or ipv6 addresses but not both at
  the same time. By default ipv4 addresses are enabled. To use ipv6
  addresses set the following properties when you start java:

  -Djava.net.preferIPv4Stack=false
  -Djava.net.preferIPv6Stack=true
  -Djava.net.preferIPv6Addresses=true
