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• The proposed changes does not require create any breaking changes to public interfacesin public interfaces. There are however changes that are done to the semantics of the listener configuration, i.e. the following configuration examples

"PLAINTEXT://127.0.0.1:9092,PLAINTEXT://[::1]:9092"
"PLAINTEXT://[::1]:9093,PLAINTEXT://127.0.0.1:9093"
"PLAINTEXT://127.0.0.1:9094,PLAINTEXT://[::1]:9094,PLAINTEXT://127.0.0.1:9095,PLAINTEXT://[::1]:9095"
"PLAINTEXT://[::1]:9096,PLAINTEXT://127.0.0.1:9096,PLAINTEXT://[::1]:9097,PLAINTEXT://127.0.0.1:9097"

Are now considered valid which means that Kafka will attempt to start with such configurations rather than short circuiting with an error. Specifically this means if and only if you have 2 listeners on the same port and one is IPv4 and the other is IPv6 then this is considered an accepted listener configuration.

Proposed Changes

In summary the proposed changes involve loosening the validation on listenerListToEndPoints in kafka.utils.CoreUtils.scala so that duplicates ports are allowed if and only if

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