les: only advertise and search for LES2 topic

les/backend.go

@@ -221,9 +221,8 @@ func (s *LightEthereum) Start(srvr *p2p.Server) error {
 	s.startBloomHandlers()
 	log.Warn("Light client mode is an experimental feature")
 	s.netRPCService = ethapi.NewPublicNetAPI(srvr, s.networkId)
-	// search the topic belonging to the oldest supported protocol because
-	// servers always advertise all supported protocols
-	protocolVersion := ClientProtocolVersions[len(ClientProtocolVersions)-1]
+	// clients are searching for the first advertised protocol in the list
+	protocolVersion := AdvertiseProtocolVersions[0]
 	s.serverPool.start(srvr, lesTopic(s.blockchain.Genesis().Hash(), protocolVersion))
 	s.protocolManager.Start()
 	return nil

les/protocol.go

@@ -41,8 +41,9 @@ const (
 
 // Supported versions of the les protocol (first is primary)
 var (
-	ClientProtocolVersions = []uint{lpv2, lpv1}
-	ServerProtocolVersions = []uint{lpv2, lpv1}
+	ClientProtocolVersions    = []uint{lpv2, lpv1}
+	ServerProtocolVersions    = []uint{lpv2, lpv1}
+	AdvertiseProtocolVersions = []uint{lpv2} // clients are searching for the first advertised protocol in the list
 )
 
 // Number of implemented message corresponding to different protocol versions.

les/server.go

@@ -56,8 +56,8 @@ func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 		return nil, err
 	}
 
-	lesTopics := make([]discv5.Topic, len(ServerProtocolVersions))
-	for i, pv := range ServerProtocolVersions {
+	lesTopics := make([]discv5.Topic, len(AdvertiseProtocolVersions))
+	for i, pv := range AdvertiseProtocolVersions {
 		lesTopics[i] = lesTopic(eth.BlockChain().Genesis().Hash(), pv)
 	}