diff --git a/Makefile b/Makefile
index 65767d0..32aff40 100755
--- a/Makefile
+++ b/Makefile
@@ -190,6 +190,7 @@ darwin-gz: env darwin ## build darwin packages
 
 ## unit test
 test: ## execute unit test
+	go clean -testcache
 	go test -v -mod=vendor -bench=. github.com/luscis/openlan/pkg/access
 	go test -v -mod=vendor -bench=. github.com/luscis/openlan/pkg/libol
 	go test -v -mod=vendor -bench=. github.com/luscis/openlan/pkg/models
diff --git a/pkg/libol/udp.go b/pkg/libol/udp.go
new file mode 100644
index 0000000..c684da7
--- /dev/null
+++ b/pkg/libol/udp.go
@@ -0,0 +1,176 @@
+package libol
+
+/*
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/ip.h>
+#include <linux/udp.h>
+#include <linux/xfrm.h>
+#include <linux/ipsec.h>
+#include <linux/pfkeyv2.h>
+#include <arpa/inet.h>
+
+typedef struct {
+    u_int32_t padding[2];
+    u_int32_t spi;
+    u_int32_t seqno;
+} udp_message;
+
+typedef struct {
+    u_int16_t port;
+    int32_t socket;
+} udp_server;
+
+typedef struct {
+    int32_t socket;
+    uint16_t remote_port;
+    const char *remote_addr;
+    u_int32_t spi;
+    u_int32_t seqno;
+} udp_connection;
+
+int seqno = 0;
+
+int send_ping_once(udp_connection *conn) {
+    int retval = 0;
+    struct sockaddr_in dstaddr = {
+        .sin_family = AF_INET,
+        .sin_port = htons(conn->remote_port),
+        .sin_addr = {
+            .s_addr = inet_addr(conn->remote_addr),
+        },
+    };
+    udp_message data = {
+        .padding = {0, 0},
+        .spi = htonl(conn->spi),
+    };
+    data.seqno = htonl(conn->seqno++);
+
+    retval = sendto(conn->socket, &data, sizeof data, 0, (struct sockaddr *)&dstaddr, sizeof dstaddr);
+    if (retval <= 0) {
+        printf("%s: could not send data\n", conn->remote_addr);
+    }
+
+    return retval;
+}
+
+int recv_ping_once(udp_connection *conn,  udp_connection *from) {
+    struct sockaddr_in addr;
+    int addrlen = sizeof addr;
+    udp_message data;
+    int datalen = sizeof data;
+    int retval = 0;
+
+    memset(&data, 0, sizeof data);
+    retval = recvfrom(conn->socket, &data, datalen, 0, (struct sockaddr *)&addr, &addrlen);
+    if ( retval <= 0 ) {
+        if (errno == EAGAIN) {
+            return 0;
+        }
+        printf("recvfrom: %s\n", strerror(errno));
+        return retval;
+    }
+
+    from->spi = ntohl(data.spi);
+	from->remote_addr = inet_ntoa(addr.sin_addr);
+	from->remote_port = ntohs(addr.sin_port);
+
+    return retval;
+}
+
+int open_socket(udp_server *srv) {
+    int op = 1;
+    struct sockaddr_in addr = {
+        .sin_family = AF_INET,
+        .sin_port = htons(srv->port),
+        .sin_addr = {
+            .s_addr = INADDR_ANY,
+        },
+    };
+	int retval = 0;
+
+    srv->socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    if (srv->socket == -1) {
+        return -1;
+    }
+
+	retval = setsockopt(srv->socket, SOL_SOCKET, SO_REUSEADDR, &op, sizeof op);
+    if (retval < 0) {
+        return -1;
+    }
+	retval = bind(srv->socket, (struct sockaddr *)&addr, sizeof addr);
+    if ( retval == -1) {
+        return -1;
+    }
+
+    return 0;
+}
+
+int configure_socket(udp_server *srv) {
+    int encap = UDP_ENCAP_ESPINUDP;
+
+    if (setsockopt(srv->socket, IPPROTO_UDP, UDP_ENCAP, &encap, sizeof encap) < 0) {
+        return -1;
+    }
+    return 0;
+}
+*/
+import "C"
+import (
+	"fmt"
+	"sync"
+	"time"
+	"unsafe"
+)
+
+func StartUDP(spi uint32, port uint16, remote string) {
+	server := &C.udp_server{
+		port: C.ushort(port),
+		socket : -1,
+	}
+	_ = C.open_socket(server)
+	C.configure_socket(server)
+
+	addr := C.CString(remote)
+	defer C.free(unsafe.Pointer(addr))
+	conn := &C.udp_connection {
+		socket: server.socket,
+		spi: C.uint(spi),
+		remote_port: C.ushort(port),
+		remote_addr: addr,
+	}
+
+	C.send_ping_once(conn)
+
+	w := sync.WaitGroup{}
+	w.Add(2)
+	Go(func() {
+		defer w.Done()
+		for i := 0; i < 100; i++ {
+			time.Sleep(time.Second)
+			C.send_ping_once(conn)
+		}
+	})
+
+	Go(func() {
+		from := &C.udp_connection{}
+		C.recv_ping_once(conn, from)
+		addr := C.GoString(from.remote_addr)
+		fmt.Printf("receive from %s:%d spi %d\n", addr, from.remote_port, from.spi)
+		w.Done()
+		for {
+			from := &C.udp_connection{}
+			C.recv_ping_once(conn, from)
+			addr := C.GoString(from.remote_addr)
+			fmt.Printf("receive from %s:%d spi %d\n", addr, from.remote_port, from.spi)
+		}
+	})
+
+	w.Wait()
+}
\ No newline at end of file
diff --git a/pkg/libol/udp_test.go b/pkg/libol/udp_test.go
new file mode 100644
index 0000000..d6d64c0
--- /dev/null
+++ b/pkg/libol/udp_test.go
@@ -0,0 +1,9 @@
+package libol
+
+import (
+	"testing"
+)
+
+func TestStartUDP_C(t *testing.T) {
+	StartUDP(84209, 4500, "180.109.49.146")
+}