func (nrc *NetworkRoutingController) enablePolicyBasedRouting() error {
	err := rtTablesAdd(customRouteTableID, customRouteTableName)
	if err != nil {
		return fmt.Errorf("failed to update rt_tables file: %s", err)
	}
	out, err := exec.Command("ip", "rule", "list").Output()
	if err != nil {
		return fmt.Errorf("failed to verify if `ip rule` exists: %s", err.Error())
	}
	if !strings.Contains(string(out), nrc.podCidr) {
		err = exec.Command("ip", "rule", "add", "from", nrc.podCidr, "lookup", customRouteTableID).Run()
		if err != nil {
			return fmt.Errorf("failed to add ip rule due to: %s", err.Error())
		}
	}
	return nil
}
setup a custom routing table that will be used for policy based routing to ensure traffic originating
on tunnel interface only leaves through tunnel interface irrespective rp_filter enabled/disabled
package routing
import (
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	"strings"
	"github.com/cloudnativelabs/kube-router/pkg/utils"
)