It appears that camel-netty4 does not set CamelNettyRemoteAddress in headers of an Exchange generated by an in-only UDP endpoint.
It does set CamelNettyRemoteAddress in properties of the exchange.
CamelNettyRemoteAddress in properties is set from AddressedEnvelope#sender(). CamelNettyRemoteAddress in headers is set from ChannelHandlerContext#channel().remoteAddress().
It appears that the latter does not actually contain the remote address. Possible solutions are:
1) Change NettyEndpoint to set CamelNettyRemoteAddress in headers from the AddressedEnvelope received
2) Change NettyEndpoint to set CamelNettyRemoteAddress from properties (and to set properties of the Exchange first)