Add back random iproute2 table index

tun_linux.go

@@ -3,6 +3,7 @@ package tun
 import (
 	"errors"
 	"fmt"
+	"math/rand"
 	"net"
 	"net/netip"
 	"os"
@@ -283,6 +284,16 @@ func (t *NativeTun) Start() error {
 		return nil
 	}
 
+	if t.options.IPRoute2TableIndex == 0 {
+		for {
+			t.options.IPRoute2TableIndex = int(rand.Uint32())
+			routeList, fErr := netlink.RouteListFiltered(netlink.FAMILY_ALL, &netlink.Route{Table: t.options.IPRoute2TableIndex}, netlink.RT_FILTER_TABLE)
+			if len(routeList) == 0 || fErr != nil {
+				break
+			}
+		}
+	}
+
 	err = t.setRoute(tunLink)
 	if err != nil {
 		_ = t.unsetRoute0(tunLink)