I'am building a local blockchain using etherium.I wrote a smart contract   "Hello" that allows to display a phrase. when I execute truffle.compile an error occurs:  No visibility specified. Did you intend to add "public"?

    pragma solidity ^0.4.15;
    contract Hello{
       string public message;
       function Hello() {
       message = "Hello, World : This is a Solidity Smart Contract on the Private Ethereum Blockchain ";
       }
    }

编译你的合同...

Compiling ./contracts/Hello.sol
Compiling ./contracts/Migrations.sol

/home/mohamed/Projects/Stage/Truffle/contracts/Hello.sol:1:1: SyntaxError: Source file requires different compiler version (current compiler is …

我想在我的本地网络上部署智能合约。我通过执行本地节点

       PRIVATE_CONFIG=ignore nohup geth --datadir ./Node1/new- 
       node-1 
       --nodiscover --verbosity 5 --networkid 31337 --raft -- 
       raftport 51001 --rpc --rpcaddr 0.0.0.0 --rpcport 22101 -- 
       rpcapi 
       admin,db,eth,debug,miner,net,shh,txpool,personal,web3, 
       quorum,raft --emitcheckpoints --port 21101 2>>node1.log &

我必须使用 localhost:\127.0.0.1:21101 或 22101？我想知道这两个端口之间的区别以及用途？

如果您不介意的话，还有一个问题：当我使用端口 21101 时，它无法连接，当我查阅节点日志时，我发现：

        Failed RLPx handshake addr=[::1]:42552  conn=inbound    
        err="read tcp [::1]:21102->[::1]:42552:  i/o timeout"