diff --git a/daemon/daemon.go b/daemon/daemon.go
index a9928dcc..b6497b13 100644
--- a/daemon/daemon.go
+++ b/daemon/daemon.go
@@ -65,6 +65,7 @@ func NewNode() *Node {
 	}
 
 	sw := p2p.NewSwitch([]p2p.Reactor{pexReactor, mempoolReactor, consensusReactor})
+	sw.SetChainId(state.Hash(), config.App().GetString("Network"))
 
 	return &Node{
 		sw:               sw,
diff --git a/p2p/pex_reactor.go b/p2p/pex_reactor.go
index 3ede6dc0..166c3c5f 100644
--- a/p2p/pex_reactor.go
+++ b/p2p/pex_reactor.go
@@ -96,6 +96,12 @@ func (pexR *PEXReactor) Receive(chId byte, src *Peer, msgBytes []byte) {
 	log.Info("Received message", "msg", msg)
 
 	switch msg.(type) {
+	case *pexHandshakeMessage:
+		chainId := msg.(*pexHandshakeMessage).ChainId
+		if chainId != pexR.sw.chainId {
+			err := fmt.Sprintf("Peer is on a different chain/network. Got %s, expected %s", chainId, pexR.sw.chainId)
+			pexR.sw.StopPeerForError(src, err)
+		}
 	case *pexRequestMessage:
 		// src requested some peers.
 		// TODO: prevent abuse.
@@ -201,9 +207,10 @@ func (pexR *PEXReactor) ensurePeers() {
 // Messages
 
 const (
-	msgTypeUnknown = byte(0x00)
-	msgTypeRequest = byte(0x01)
-	msgTypeAddrs   = byte(0x02)
+	msgTypeUnknown   = byte(0x00)
+	msgTypeRequest   = byte(0x01)
+	msgTypeAddrs     = byte(0x02)
+	msgTypeHandshake = byte(0x03)
 )
 
 // TODO: check for unnecessary extra bytes at the end.
@@ -213,6 +220,8 @@ func DecodeMessage(bz []byte) (msg interface{}, err error) {
 	r := bytes.NewReader(bz)
 	// log.Debug(Fmt("decoding msg bytes: %X", bz))
 	switch msgType {
+	case msgTypeHandshake:
+		msg = binary.ReadBinary(&pexHandshakeMessage{}, r, n, &err)
 	case msgTypeRequest:
 		msg = &pexRequestMessage{}
 	case msgTypeAddrs:
@@ -223,6 +232,19 @@ func DecodeMessage(bz []byte) (msg interface{}, err error) {
 	return
 }
 
+/*
+A pexHandshakeMessage contains the peer's chainId
+*/
+type pexHandshakeMessage struct {
+	ChainId string
+}
+
+func (m *pexHandshakeMessage) TypeByte() byte { return msgTypeHandshake }
+
+func (m *pexHandshakeMessage) String() string {
+	return "[pexHandshake]"
+}
+
 /*
 A pexRequestMessage requests additional peer addresses.
 */
diff --git a/p2p/switch.go b/p2p/switch.go
index b9696d24..0b348003 100644
--- a/p2p/switch.go
+++ b/p2p/switch.go
@@ -1,6 +1,7 @@
 package p2p
 
 import (
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"net"
@@ -37,6 +38,7 @@ type Switch struct {
 	quit         chan struct{}
 	started      uint32
 	stopped      uint32
+	chainId      string
 }
 
 var (
@@ -129,6 +131,10 @@ func (sw *Switch) AddPeerWithConnection(conn net.Conn, outbound bool) (*Peer, er
 	// Notify listeners.
 	sw.doAddPeer(peer)
 
+	// Send handshake
+	msg := &pexHandshakeMessage{ChainId: sw.chainId}
+	peer.Send(PexCh, msg)
+
 	return peer, nil
 }
 
@@ -216,6 +222,10 @@ func (sw *Switch) StopPeerGracefully(peer *Peer) {
 	sw.doRemovePeer(peer, nil)
 }
 
+func (sw *Switch) SetChainId(hash []byte, network string) {
+	sw.chainId = hex.EncodeToString(hash) + "-" + network
+}
+
 func (sw *Switch) IsListening() bool {
 	return sw.listeners.Size() > 0
 }