This is a one off failure observed on JDK 11 CI

----------System.err:(15/803)----------
java.lang.Exception: packets not the same
at Tests.comparePackets(Tests.java:148)
at Tests.simpleDataExchange(Tests.java:101)
at UdpTest.test1(UdpTest.java:93)
at UdpTest.main(UdpTest.java:80)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:298)
at java.base/java.lang.Thread.run(Thread.java:834)

This test could benefit from additional logging info - in particular - what was in the packets that did not match, and what addresses where used on both sides. Possibly the test should be hardened to reject packets that were not emitted by the test itself. Also the test should use try-with-resource to ensure that sockets are properly closed, and should preferably be run in /othervm to avoid potential limitation on datagram sockets in the agent VM.

Note that JDK 11 still has the old DatagramSocket implementation. I haven't observed this particular failure on the latest JDK yet.
This is a different failure than those observed in JDK-8198266