golang set icmp ttl

Golang is a very popular programming language and is widely used in network programming and system programming. In network programming, setting ICMP Time-To-Live (TTL) is a very important task, which can help us detect and diagnose network connection problems. This article will introduce how to set ICMP TTL using Golang language.

What is ICMP TTL?

On the Internet, the IP protocol is one of the core protocols used to transmit data packets in the network. When the IP protocol transmits data packets, it hands the data packets to the underlying network device for routing and forwarding. In order to prevent data packets from endless loops in the network, the IP protocol uses a TTL mechanism to limit the survival time of data packets in the network. TTL means survival time, that is to say, every time a data packet is forwarded by the router, the TTL value will be reduced by 1. When the TTL value is reduced to 0, the packet will be discarded and an ICMP Time Exceeded message will be sent to inform the source address.

Why do you need to set ICMP TTL?

When we are troubleshooting network connections, ICMP TTL is one of the most important pieces of information. By detecting the ICMP Time Exceeded message, we can learn the number of routers passing from the source address to the destination address. This helps us analyze the root causes of failures in network connections, such as unstable network topology, incorrect router configuration, etc.

How to set ICMP TTL using Golang?

In Golang, setting ICMP TTL is actually very simple. You only need to use the IPConn object and IP header structure in the net package. Below is a simple Golang program that sends a PING request with a TTL of 100 and receives the response.

package main

import (
    "fmt"
    "net"
    "os"
    "time"
)

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)
    if err != nil {
        fmt.Println("Error:", err.Error())
        os.Exit(1)
    }

    var msg [512]byte

    msg[0] = 8 // echo
    msg[1] = 0 // code
    msg[2] = 0 // checksum
    msg[3] = 0 // checksum
    msg[4] = 0 // identifier[0]
    msg[5] = 13 // identifier[1]
    msg[6] = 0 // sequence[0]
    msg[7] = 37 // sequence[1]

    for i := 8; i < len(msg); i++ {
        msg[i] = byte(i - 8)
    }

    // Set TTL to 100
    if err := conn.SetTTL(100); err != nil {
        fmt.Println("Error:", err.Error())
        os.Exit(1)
    }

    start := time.Now()

    _, err = conn.Write(msg[0:64])
    if err != nil {
        fmt.Println("Error:", err.Error())
        os.Exit(1)
    }

    conn.SetReadDeadline(time.Now().Add(time.Second * 5))

    var buf [512]byte
    n, err := conn.Read(buf[0:])
    if err != nil {
        fmt.Println("Error:", err.Error())
        os.Exit(1)
    }

    elapsed := time.Since(start)

    fmt.Printf("%d bytes from %s: time=%v
", n, service, elapsed)
}

The core part of this code lies in the conn.SetTTL(100) line, which is used to set the ICMP TTL value to 100. The other parts are very similar to the standard PING program code, which is used to send ICMP requests and wait for responses.

Note that because some operations in the net package require administrator privileges to perform, you may need a privileged user or root privileges when running this program.

Summary

This article introduces how to use Golang language to set ICMP TTL. Through this function, we can detect and diagnose network connection problems, thereby better maintaining network equipment and services. Golang's standard library provides a very convenient network programming interface, making network programming easier and more efficient. If you also need to do network programming, Golang is a great choice.

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