diff --git a/eth/backend.go b/eth/backend.go
index 83e05e96a8..89e379dbc4 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -141,6 +141,10 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 	}
 	log.Info("Initialised chain configuration", "config", chainConfig)
 
+	networkID := config.NetworkId
+	if networkID == 0 {
+		networkID = chainConfig.ChainID.Uint64()
+	}
 	eth := &Ethereum{
 		config:         config,
 		chainDb:        chainDb,
@@ -148,7 +152,7 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 		accountManager: ctx.AccountManager,
 		engine:         CreateConsensusEngine(ctx, chainConfig, &config.Ethash, config.Miner.Notify, config.Miner.Noverify, chainDb),
 		shutdownChan:   make(chan bool),
-		networkID:      config.NetworkId,
+		networkID:      networkID,
 		gasPrice:       config.Miner.GasPrice,
 		etherbase:      config.Miner.Etherbase,
 		bloomRequests:  make(chan chan *bloombits.Retrieval),
@@ -160,7 +164,7 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 	if bcVersion != nil {
 		dbVer = fmt.Sprintf("%d", *bcVersion)
 	}
-	log.Info("Initialising Ethereum protocol", "versions", ProtocolVersions, "network", config.NetworkId, "dbversion", dbVer)
+	log.Info("Initialising Ethereum protocol", "versions", ProtocolVersions, "network", networkID, "dbversion", dbVer)
 
 	if !config.SkipBcVersionCheck {
 		if bcVersion != nil && *bcVersion > core.BlockChainVersion {
@@ -207,7 +211,7 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 	if checkpoint == nil {
 		checkpoint = params.TrustedCheckpoints[genesisHash]
 	}
-	if eth.protocolManager, err = NewProtocolManager(chainConfig, checkpoint, config.SyncMode, config.NetworkId, eth.eventMux, eth.txPool, eth.engine, eth.blockchain, chainDb, cacheLimit, config.Whitelist); err != nil {
+	if eth.protocolManager, err = NewProtocolManager(chainConfig, checkpoint, config.SyncMode, networkID, eth.eventMux, eth.txPool, eth.engine, eth.blockchain, chainDb, cacheLimit, config.Whitelist); err != nil {
 		return nil, err
 	}
 	eth.miner = miner.New(eth, &config.Miner, chainConfig, eth.EventMux(), eth.engine, eth.isLocalBlock)
diff --git a/eth/config.go b/eth/config.go
index 5094a533bf..d0ab2ed258 100644
--- a/eth/config.go
+++ b/eth/config.go
@@ -43,7 +43,7 @@ var DefaultConfig = Config{
 		DatasetsInMem:  1,
 		DatasetsOnDisk: 2,
 	},
-	NetworkId:          1,
+	NetworkId:          0,
 	LightPeers:         100,
 	UltraLightFraction: 75,
 	DatabaseCache:      512,
@@ -91,8 +91,10 @@ type Config struct {
 	// If nil, the Ethereum main net block is used.
 	Genesis *core.Genesis `toml:",omitempty"`
 
-	// Protocol options
-	NetworkId uint64 // Network ID to use for selecting peers to connect to
+	// Network ID separates blockchains on the peer-to-peer networking level. When left
+	// zero, the chain ID is used as network ID.
+	NetworkId uint64
+
 	SyncMode  downloader.SyncMode
 
 	NoPruning  bool // Whether to disable pruning and flush everything to disk