I'm afraid the question isn't related to the Go programming language at
all. It's related to the operating system you're running on - which as far
as I can see, you haven't mentioned. It's whatever the underlying system
calls and TCP stack do.
On Tuesday, 22 June 2021 at 16:40:16 UTC+1 chanda...@gmail.com wrote:
> Written one TCP client which is used to create 10 TCP concurrent
> connections(holding for logger time) and enable only 10 ephemeral ports to
> use(49001 - 49010 ip_local_port_range file).
>
> func createConnection(c int, desAddr, desPort string) (brokerCon net.Conn,
> err error) {
> localips := GetLocalIP()
> maxRetry := len(localips)
> retry := 0
> for retry < maxRetry {
> lIPPort := fmt.Sprintf("%s:0",
> strings.Split(localips[retry].String(), "/")[0])
> fmt.Println("\n---", lIPPort)
> laddr, lerr := net.ResolveTCPAddr("tcp4", lIPPort)
> if lerr != nil {
> fmt.Println("Getting Error ResolveTCPAddr for local ", lerr)
> }
> raddr, rerr := net.ResolveTCPAddr("tcp4", desAddr+desPort)
> if rerr != nil {
> fmt.Println("Getting Error ResolveTCPAddr for local ", rerr)
> }
>
> brokerCon, err = net.DialTCP("tcp", laddr, raddr)
> if err != nil {
> fmt.Printf("Failed to connect connetion %d , %d retrying with
> seconday IP, err:\n",
> c, retry, err)
> retry = retry + 1
> time.Sleep(1 * time.Second)
> continue
>
> } else {
> //fmt.Println("successfull ")
> break
> }
> }
> return
> }
>
>
> *Scenario 1:*
>
> It's able to create 10 connections if the laddr value is *nil* on the
> DialTCP method. DialTCP is able to use 49009 and 49007 port which is
> already used by some different destination(as because A TCP connection is
> determined by a 5-tuple: *[local IP, local port, remote IP, remote port,
> protocol]* )
>
> sudo netstat -anpl --tcp --udp | grep 490
>
> tcp 0 0 10.50.1.245:49005 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49010 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49008 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49009 XXX.XXX.XXX.X44:443
> ESTABLISHED 3250/XXXX
>
> tcp 0 0 10.50.1.245:49006 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49002 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49004 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49001 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49007 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49003 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> tcp 0 0 10.50.1.245:49007 XXX.XXX.XXX.X29:443
> ESTABLISHED 2806/XXXX
>
> tcp 0 0 10.50.1.245:49009 10.50.1.41:9999
> ESTABLISHED 23408/client
>
> *Scenario 2:*
>
> If I Pass local IP details(10.50.1.245) with 0 port, it's able to create
> only 8 connections and throwing *bind: address already in use* for the
> remaining 2 connections. if the local address is not nil why dialTCP is not
> able to use 49005 and 49007 port which is already used by some different
> destination.
>
> sudo netstat -anpl --tcp --udp | grep 490
>
> tcp 0 0 10.50.1.245:49010 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49005 XXX.XXX.XXX.X66:443
> ESTABLISHED 2510/XXX
>
> tcp 0 0 10.50.1.245:49008 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49005 XXX.XXX.XXX.X44:443
> ESTABLISHED 3250/XXX
>
> tcp 0 0 10.50.1.245:49006 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49002 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49004 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49001 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49003 10.50.1.41:9999
> ESTABLISHED 25841/client
>
> tcp 0 0 10.50.1.245:49007 XXX.XXX.XXX.X29:443
> ESTABLISHED 2806/XXX
>
> tcp 0 0 10.50.1.245:49009 10.50.1.41:9999
> ESTABLISHED 25841/client
>
>
>
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