README.md

How to run:

go build udp.go; sudo bash -c "ulimit -n 100000; ./udpserver"
go build udpclient.go && ./udpclient
sudo netstat -l4np --udp|grep :1234|tr -s " "|egrep -v "p 0"

Sample output

127.0.87.133:1234    0.347 ms
127.0.123.255:1234   0.268 ms
127.0.152.154:1234   0.263 ms
127.0.116.156:1234   0.252 ms
127.0.62.151:1234    0.274 ms
127.0.120.152:1234   0.172 ms
...

udpclient.go

package main

import (
	"fmt"
	"math/rand"
	"net"
	"os"
	"time"
)

func main() {
	readbuf := make([]byte, 4096)
	writebuf := []byte("behlod!")

	for {
		i := 1 + rand.Intn(255)
		j := 1 + rand.Intn(255)
		addrStr := fmt.Sprintf("127.0.%d.%d:1234", i, j)
		addr, err := net.ResolveUDPAddr("udp", addrStr)
		if err != nil {
			fmt.Fprintf(os.Stderr, "net.ResolveUDPAddr() %v\n", err)
			os.Exit(3)
		}

		t0 := time.Now()
		cli, err := net.DialUDP("udp", nil, addr)
		if err != nil {
			fmt.Fprintf(os.Stderr, "net.DialUDP() %v\n", err)
			os.Exit(3)
		}

		_, err = cli.Write(writebuf)
		if err != nil {
			panic("")
		}
		_, err = cli.Read(readbuf[:])
		if err != nil {
			panic("")
		}
		td := time.Now().Sub(t0)
		fmt.Printf("%-20s %.3f ms\n",
			addrStr,
			float64(td.Nanoseconds()) / 1000. / 1000.)
		cli.Close()
		time.Sleep(200 * time.Millisecond)
	}
}

udpserver.go

package main

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

func main() {

	for i := 1; i< 256; i++ {
		for j := 1; j< 256; j++ {
			addrStr := fmt.Sprintf("127.0.%d.%d:1234", i, j)
			addr, err := net.ResolveUDPAddr("udp", addrStr)
			if err != nil {
				fmt.Fprintf(os.Stderr, "net.ResolveUDPAddr() %v\n", err)
				os.Exit(3)
			}

			srv, err := net.ListenUDP("udp", addr)
			if err != nil {
				fmt.Fprintf(os.Stderr, "net.ListenUDP() %v\n", err)
				os.Exit(3)
			}

			go func (){
				buf := make([]byte, 4096)
				for  {
					n, caddr, err := srv.ReadFromUDP(buf[:])
					if err != nil {
						fmt.Fprintf(os.Stderr, "Recv %v\n", err)
						os.Exit(3)
					}
					srv.WriteToUDP(buf[:n], caddr)
				}
			}()
		}
	}
	for {
		time.Sleep(1 * time.Second)
	}
}