dnstest -- query dns from different source ports range to debug network card losing packets from specific 5tuples

0dnstest.go

package main
 
import (
        "flag"
        "fmt"
        "net"
        "sync"
 
        "github.com/miekg/dns"
)
 
var (
        domain    string
        dnsServer string
 
        sourcePortMin int
        sourcePortMax int
 
        maxJobs     int
        maxAttempts int
)
 
func main() {
        flag.IntVar(&sourcePortMin, "sport-min", 50000, "min source port (inclusive)")
        flag.IntVar(&sourcePortMax, "sport-max", 50002, "min source port (exclusive)")
        flag.IntVar(&maxJobs, "J", 16, "max parallell requests")
        flag.IntVar(&maxAttempts, "max-attempts", 3, "max attempts to resolve from one sport")
        flag.StringVar(&dnsServer, "S", "0.0.0.0:53", "dns server to use")
        flag.StringVar(&domain, "D", "ya.ru", "domain to resolve")
        flag.Parse()
 
        sem := make(chan struct{}, maxJobs)
        var wg sync.WaitGroup
 
        for sourcePort := sourcePortMin; sourcePort < sourcePortMax; sourcePort++ {
                wg.Add(1)
                go func(sPort int) {
                        sem <- struct{}{}
                        var err error
                        for attempt := 0; attempt < maxAttempts; attempt++ {
                                _, err = resolveARecord(domain, dnsServer, sPort)
                                if err == nil {
                                        break
                                }
                        }
                        if err != nil {
                                fmt.Printf("sPort: %d err: %v\n", sPort, err)
                        }
                        <-sem
                        wg.Done()
                }(sourcePort)
        }
 
        wg.Wait()
}
 
// resolveARecord resolves the A record of a given domain using the specified DNS server and UDP source port
func resolveARecord(domain, dnsServer string, sourcePort int) (string, error) {
        client := dns.Client{Net: "udp", Dialer: &net.Dialer{LocalAddr: &net.UDPAddr{IP: net.IPv4zero, Port: sourcePort}}}
 
        // Prepare DNS message
        msg := new(dns.Msg)
        msg.SetQuestion(domain+".", dns.TypeA)
 
        // Send DNS query message
        response, _, err := client.Exchange(msg, dnsServer)
        if err != nil {
                return "", err
        }
 
        // Check if response contains answers
        if len(response.Answer) == 0 {
                return "", fmt.Errorf("No answer records found")
        }
 
        // Extract IP address from the first answer
        ipAddress := response.Answer[0].(*dns.A).A.String()
 
        return ipAddress, nil
}

go.mod

module dnstest
 
go 1.21.4
 
require github.com/miekg/dns v1.1.58
 
require (
        golang.org/x/mod v0.14.0 // indirect
        golang.org/x/net v0.20.0 // indirect
        golang.org/x/sys v0.16.0 // indirect
        golang.org/x/tools v0.17.0 // indirect
)

go.sum

github.com/miekg/dns v1.1.58 h1:ca2Hdkz+cDg/7eNF6V56jjzuZ4aCAE+DbVkILdQWG/4=
github.com/miekg/dns v1.1.58/go.mod h1:Ypv+3b/KadlvW9vJfXOTf300O4UqaHFzFCuHz+rPkBY=
golang.org/x/mod v0.14.0 h1:dGoOF9QVLYng8IHTm7BAyWqCqSheQ5pYWGhzW00YJr0=
golang.org/x/mod v0.14.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
golang.org/x/net v0.20.0 h1:aCL9BSgETF1k+blQaYUBx9hJ9LOGP3gAVemcZlf1Kpo=
golang.org/x/net v0.20.0/go.mod h1:z8BVo6PvndSri0LbOE3hAn0apkU+1YvI6E70E9jsnvY=
golang.org/x/sync v0.6.0 h1:5BMeUDZ7vkXGfEr1x9B4bRcTH4lpkTkpdh0T/J+qjbQ=
golang.org/x/sync v0.6.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
golang.org/x/sys v0.16.0 h1:xWw16ngr6ZMtmxDyKyIgsE93KNKz5HKmMa3b8ALHidU=
golang.org/x/sys v0.16.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
golang.org/x/tools v0.17.0 h1:FvmRgNOcs3kOa+T20R1uhfP9F6HgG2mfxDv1vrx1Htc=
golang.org/x/tools v0.17.0/go.mod h1:xsh6VxdV005rRVaS6SSAf9oiAqljS7UZUacMZ8Bnsps=