diff --git a/eth/backend.go b/eth/backend.go
index af03517792..8734100684 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -148,6 +148,10 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	if err != nil {
 		return nil, err
 	}
+	networkID := config.NetworkId
+	if networkID == 0 {
+		networkID = chainConfig.ChainID.Uint64()
+	}
 	eth := &Ethereum{
 		config:            config,
 		merger:            consensus.NewMerger(chainDb),
@@ -156,7 +160,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 		accountManager:    stack.AccountManager(),
 		engine:            engine,
 		closeBloomHandler: make(chan struct{}),
-		networkID:         config.NetworkId,
+		networkID:         networkID,
 		gasPrice:          config.Miner.GasPrice,
 		etherbase:         config.Miner.Etherbase,
 		bloomRequests:     make(chan chan *bloombits.Retrieval),
@@ -169,7 +173,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	if bcVersion != nil {
 		dbVer = fmt.Sprintf("%d", *bcVersion)
 	}
-	log.Info("Initialising Ethereum protocol", "network", config.NetworkId, "dbversion", dbVer)
+	log.Info("Initialising Ethereum protocol", "network", networkID, "dbversion", dbVer)
 
 	if !config.SkipBcVersionCheck {
 		if bcVersion != nil && *bcVersion > core.BlockChainVersion {
@@ -232,7 +236,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 		Chain:          eth.blockchain,
 		TxPool:         eth.txPool,
 		Merger:         eth.merger,
-		Network:        config.NetworkId,
+		Network:        networkID,
 		Sync:           config.SyncMode,
 		BloomCache:     uint64(cacheLimit),
 		EventMux:       eth.eventMux,
@@ -266,7 +270,7 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	}
 
 	// Start the RPC service
-	eth.netRPCService = ethapi.NewNetAPI(eth.p2pServer, config.NetworkId)
+	eth.netRPCService = ethapi.NewNetAPI(eth.p2pServer, networkID)
 
 	// Register the backend on the node
 	stack.RegisterAPIs(eth.APIs())
diff --git a/eth/ethconfig/config.go b/eth/ethconfig/config.go
index 55441a2cb9..b708e7a673 100644
--- a/eth/ethconfig/config.go
+++ b/eth/ethconfig/config.go
@@ -60,7 +60,7 @@ var LightClientGPO = gasprice.Config{
 // Defaults contains default settings for use on the Ethereum main net.
 var Defaults = Config{
 	SyncMode:           downloader.SnapSync,
-	NetworkId:          1,
+	NetworkId:          0,
 	TxLookupLimit:      2350000,
 	TransactionHistory: 2350000,
 	StateHistory:       params.FullImmutabilityThreshold,
@@ -89,8 +89,9 @@ 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
 
 	// This can be set to list of enrtree:// URLs which will be queried for