Nacos client connection operation 9848 grpc connection error of Nacos 2.0

After Nacos Server 2.0

Nacos version 2.0 adds a new gRPC communication method compared to 1.X, so 2 additional ports are needed. The new ports are automatically generated by performing a certain offset from the configured master port (server.port).
Port Offset from the master port Description
9848 1000 Client gRPC request server port for clients to initiate connections and requests to the server
9849 1001 Server-side gRPC request server port, used for synchronization between services, etc.

After Nacos client 2.0 is connected through grpc, you cannot use Nacos server version below 2.0

serverInfo.getServerPort() + rpcPortOffset() Port offset 1000
Perform serverCheck operation 
Report an error.
java.util.concurrent.ExecutionException: com.alibaba.nacos.shaded.io.grpc.StatusRuntimeException: UNAVAILABLE: io exception
Error: RpcClient currentConnection is null
Caused by: ErrCode:-401, ErrMsg:Client not connected,current status:STARTING

Solution: use a lower version of Nacos client