diff --git a/cmd/cli/os_linux.go b/cmd/cli/os_linux.go
index 1607f25..c0c8125 100644
--- a/cmd/cli/os_linux.go
+++ b/cmd/cli/os_linux.go
@@ -160,6 +160,7 @@ func resetDNS(iface *net.Interface) (err error) {
 	}
 
 	// TODO(cuonglm): handle DHCPv6 properly.
+	mainLog.Load().Debug().Msg("checking for IPv6 availability")
 	if ctrldnet.IPv6Available(ctx) {
 		c := client6.NewClient()
 		conversation, err := c.Exchange(iface.Name)
@@ -179,6 +180,8 @@ func resetDNS(iface *net.Interface) (err error) {
 				}
 			}
 		}
+	} else {
+		mainLog.Load().Debug().Msg("IPv6 is not available")
 	}
 
 	return ignoringEINTR(func() error {
diff --git a/internal/clientinfo/mdns.go b/internal/clientinfo/mdns.go
index 3c8af6e..23342b3 100644
--- a/internal/clientinfo/mdns.go
+++ b/internal/clientinfo/mdns.go
@@ -102,11 +102,14 @@ func (m *mdns) init(quitCh chan struct{}) error {
 			v4ConnList = append(v4ConnList, conn)
 			go m.readLoop(conn)
 		}
+		ctrld.ProxyLogger.Load().Debug().Msgf("checking for IPv6 availability in mdns init")
 		if ctrldnet.IPv6Available(context.Background()) {
 			if conn, err := net.ListenMulticastUDP("udp6", &iface, mdnsV6Addr); err == nil {
 				v6ConnList = append(v6ConnList, conn)
 				go m.readLoop(conn)
 			}
+		} else {
+			ctrld.ProxyLogger.Load().Debug().Msgf("IPv6 is not available in mdns init")
 		}
 	}
 
diff --git a/internal/net/net.go b/internal/net/net.go
index 3a81849..dd1c072 100644
--- a/internal/net/net.go
+++ b/internal/net/net.go
@@ -49,8 +49,12 @@ func init() {
 }
 
 func supportIPv6(ctx context.Context) bool {
-	_, err := probeStackDialer.DialContext(ctx, "tcp6", net.JoinHostPort(controldIPv6Test, "443"))
-	return err == nil
+	c, err := probeStackDialer.DialContext(ctx, "tcp6", v6BootstrapDNS)
+	if err != nil {
+		return false
+	}
+	c.Close()
+	return true
 }
 
 func supportListenIPv6Local() bool {
diff --git a/net.go b/net.go
index 3ae3bb5..449620d 100644
--- a/net.go
+++ b/net.go
@@ -18,6 +18,7 @@ const ipv6ProbingInterval = 10 * time.Second
 
 func hasIPv6() bool {
 	hasIPv6Once.Do(func() {
+		Log(context.Background(), ProxyLogger.Load().Debug(), "checking for IPv6 availability once")
 		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 		defer cancel()
 		val := ctrldnet.IPv6Available(ctx)
@@ -43,6 +44,7 @@ func probingIPv6(ctx context.Context, old bool) {
 				if ipv6Available.CompareAndSwap(old, cur) {
 					old = cur
 				}
+				Log(ctx, ProxyLogger.Load().Debug(), "IPv6 availability: %v", cur)
 			}()
 		}
 	}