Tutorial: Automate GTP-U tunnel creation using Go

In the last tutorial, we created a GTP-U tunnel on a Ubuntu virtual machine using Open Vswitch. Here we will take the next step and write a Go program that programatically creates such tunnels.

Pre-requisites

• a Ubuntu 22.04 machine

Install OVS:

sudo apt update
sudo apt install openvswitch-switch

Create a folder named tunnel-go :

mkdit tunnel-go
cd tunnel-go

Create a new go module:

go mod init tunnel-go

Create a main.go file with an empty main function:

package main

func main() {}

Import Digital Ocean’s OVS Go library as well as the log standard library:

package main

import (
 "log"

 "github.com/digitalocean/go-openvswitch/ovs"
)

func main() {
}

Use the OVS library to create a client:

ovsClient := ovs.New(
  ovs.Sudo(),
 )

With this client, create a bridge named br0 :

if err := ovsClient.VSwitch.AddBridge(ovsBridge); err != nil {
  log.Fatalf("failed to add bridge: %v", err)
 }

Use the netdev datapath:

if err := ovsClient.VSwitch.Set.Bridge(ovsBridge, ovs.BridgeOptions{
  DataPathType: ovs.DataPathTypeNetDev,
 }); err != nil {
  log.Fatalf("failed to set bridge: %v", err)
 }

Create the enp6s0 and enp7s0 ports:

if err := ovsClient.VSwitch.AddPort(ovsBridge, ranPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

if err := ovsClient.VSwitch.AddPort(ovsBridge, dataPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

Create the GTP-U tunnel:

if err := ovsClient.VSwitch.AddPort(ovsBridge, gtpuPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

if err := ovsClient.VSwitch.Set.Interface(gtpuPort, ovs.InterfaceOptions{
  Type:     "gtpu",
  RemoteIP: gtpuRemoteIP,
  Key:      gtpuTEID,
 }); err != nil {
  log.Fatalf("failed to set interface: %v", err)
 }

There you go, you have created a program that can create GTP-U tunnels! 🎊

Here’s the complete code:

package main

import (
 "log"

 "github.com/digitalocean/go-openvswitch/ovs"
)

func main() {
 CreateGTPUTunnel()
}

func CreateGTPUTunnel() {
 var ovsBridge string = "br0"
 var ranPort string = "ran"
 var dataPort string = "data"
 var gtpuPort string = "gtpu0"
 var gtpuRemoteIP string = "172.31.1.1"
 var gtpuTEID string = "5000"

 ovsClient := ovs.New(
  ovs.Sudo(),
 )

 // sudo ovs-vsctl add-br br0
 if err := ovsClient.VSwitch.AddBridge(ovsBridge); err != nil {
  log.Fatalf("failed to add bridge: %v", err)
 }

 // sudo ovs-vsctl set bridge br0 datapath_type=netdev
 if err := ovsClient.VSwitch.Set.Bridge(ovsBridge, ovs.BridgeOptions{
  DataPathType: ovs.DataPathTypeNetDev,
 }); err != nil {
  log.Fatalf("failed to set bridge: %v", err)
 }

 // sudo ovs-vsctl add-port br0 enp6s0
 if err := ovsClient.VSwitch.AddPort(ovsBridge, ranPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

 // sudo ovs-vsctl add-port br0 enp7s0
 if err := ovsClient.VSwitch.AddPort(ovsBridge, dataPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

 // sudo ovs-vsctl add-port br0 gtpu0
 if err := ovsClient.VSwitch.AddPort(ovsBridge, gtpuPort); err != nil {
  log.Fatalf("failed to add port: %v", err)
 }

 // sudo ovs-vsctl set int gtpu0 type=gtpu options:key=5000 options:remote_ip=172.31.1.1
 if err := ovsClient.VSwitch.Set.Interface(gtpuPort, ovs.InterfaceOptions{
  Type:     "gtpu",
  RemoteIP: gtpuRemoteIP,
  Key:      gtpuTEID,
 }); err != nil {
  log.Fatalf("failed to set interface: %v", err)
 }

}