The Java broker supports multiple version of the AMQP protocol (0-8,0-9,0-9-1,0-10), and allows disabling specific versions on specific (or all) ports. It would be useful if the default version reply to an unsupported protocol version initiation attempt could be configured, to allow controlling behaviour of the broker in this situation.
For example, a broker could have 0-8, 0-9, 0-9-1 enabled on one port and 0-10 enabled on another. In this state, a legacy client supporting 0-9 and 0-10 but not 0-9-1 would be unable to connect to the first port because the broker will reply with 0-9-1 if the client initially attempts 0-10. If the broker could be configured to reply with 0-9 instead in this case the legacy client would then be able to connect, and any newer clients could still connect on this port if simply using 0-9-1 directly.