关于 icmp 本地网络可以， 外网不可以的问题（用系统自带ping可以的），请教

```go package main import ( "bytes" "encoding/binary" "fmt" "net" "os" "time" ) type ICMP struct { Type uint8 Code uint8 Checksum uint16 Identifier uint16 SequenceNum uint16 } func CheckSum(data []byte) uint16 { var ( sum uint32 = 0 length int = len(data) index int = 0 ) for length > 1 { sum += uint32(data[index])<<8 + uint32(data[index+1]) index += 2 length -= 2 } //if length > 0 { // sum += uint32(data[index]) //} sum += (sum >> 16) return uint16(^sum) } func main() { if len(os.Args) != 2 { fmt.Println("Usage: ", os.Args[0], "host") os.Exit(1) } service := os.Args[1] conn, err := net.Dial("ip4:icmp", service) checkError(err) var icmp ICMP icmp.Type = 8 //8->echo message 0->reply message icmp.Code = 0 icmp.Checksum = 0 icmp.Identifier = 0x8888 icmp.SequenceNum = 0xB88B var buffer bytes.Buffer binary.Write(&buffer, binary.BigEndian, icmp) // icmp.Checksum = CheckSum(buffer.Bytes()) fmt.Println(buffer) buffer.Reset() binary.Write(&buffer, binary.BigEndian, icmp) fmt.Println(buffer) _, err = conn.Write(buffer.Bytes()) checkError(err) msg := make([]byte, 1024) //var msg [512]byte conn.SetReadDeadline(time.Now().Add(time.Second * 6)) _, err = conn.Read(msg) checkError(err) fmt.Println("Got response") fmt.Println("TTL = ", msg[8]) os.Exit(0) } func checkError(err error) { if err != nil { fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error()) os.Exit(1) } } ```