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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