diff --git a/net/conn/handshake.go b/net/conn/handshake.go
index ab8cea8e3..9a155c5a1 100644
--- a/net/conn/handshake.go
+++ b/net/conn/handshake.go
@@ -6,9 +6,11 @@ import (
 
 	handshake "github.com/jbenet/go-ipfs/net/handshake"
 	hspb "github.com/jbenet/go-ipfs/net/handshake/pb"
+	u "github.com/jbenet/go-ipfs/util"
 
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
 	proto "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/goprotobuf/proto"
+	ma "github.com/jbenet/go-multiaddr"
 )
 
 // Handshake1 exchanges local and remote versions and compares them
@@ -65,6 +67,10 @@ func Handshake3(ctx context.Context, c Conn) error {
 
 	var remoteH, localH *hspb.Handshake3
 	localH = handshake.Handshake3Msg(lpeer)
+
+	rma := c.RemoteMultiaddr()
+	localH.ObservedAddr = proto.String(rma.String())
+
 	localB, err := proto.Marshal(localH)
 	if err != nil {
 		return err
@@ -101,3 +107,18 @@ func Handshake3(ctx context.Context, c Conn) error {
 
 	return nil
 }
+
+func CheckNAT(obsaddr string) (bool, error) {
+	oma, err := ma.NewMultiaddr(obsaddr)
+	if err != nil {
+		return false, err
+	}
+	addrs, err := u.GetLocalAddresses()
+	if err != nil {
+		return false, err
+	}
+	_ = oma
+	_ = addrs
+
+	panic("not yet implemented!")
+}
diff --git a/net/handshake/pb/handshake.pb.go b/net/handshake/pb/handshake.pb.go
index 2308297b9..2e641cdf5 100644
--- a/net/handshake/pb/handshake.pb.go
+++ b/net/handshake/pb/handshake.pb.go
@@ -14,15 +14,11 @@ It has these top-level messages:
 */
 package handshake_pb
 
-import proto "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/gogoprotobuf/proto"
-import json "encoding/json"
+import proto "code.google.com/p/gogoprotobuf/proto"
 import math "math"
 
-// discarding unused import mux "github.com/jbenet/go-ipfs/net/mux/mux.pb"
-
-// Reference proto, json, and math imports to suppress error if they are not otherwise used.
+// Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal
-var _ = &json.SyntaxError{}
 var _ = math.Inf
 
 // Handshake1 is delivered _before_ the secure channel is initialized
@@ -56,8 +52,10 @@ func (m *Handshake1) GetAgentVersion() string {
 // Handshake3 is delivered _after_ the secure channel is initialized
 type Handshake3 struct {
 	// listenAddrs are the multiaddrs this node listens for open connections on
-	ListenAddrs      [][]byte `protobuf:"bytes,2,rep,name=listenAddrs" json:"listenAddrs,omitempty"`
-	XXX_unrecognized []byte   `json:"-"`
+	ListenAddrs [][]byte `protobuf:"bytes,2,rep,name=listenAddrs" json:"listenAddrs,omitempty"`
+	// we'll have more fields here later.
+	ObservedAddr     *string `protobuf:"bytes,4,opt,name=observedAddr" json:"observedAddr,omitempty"`
+	XXX_unrecognized []byte  `json:"-"`
 }
 
 func (m *Handshake3) Reset()         { *m = Handshake3{} }
@@ -71,5 +69,12 @@ func (m *Handshake3) GetListenAddrs() [][]byte {
 	return nil
 }
 
+func (m *Handshake3) GetObservedAddr() string {
+	if m != nil && m.ObservedAddr != nil {
+		return *m.ObservedAddr
+	}
+	return ""
+}
+
 func init() {
 }
diff --git a/net/handshake/pb/handshake.proto b/net/handshake/pb/handshake.proto
index 61e773b88..1e795d881 100644
--- a/net/handshake/pb/handshake.proto
+++ b/net/handshake/pb/handshake.proto
@@ -1,6 +1,6 @@
 package handshake.pb;
 
-import "github.com/jbenet/go-ipfs/net/mux/mux.proto";
+//import "github.com/jbenet/go-ipfs/net/mux/mux.proto";
 
 // Handshake1 is delivered _before_ the secure channel is initialized
 message Handshake1 {
@@ -30,4 +30,5 @@ message Handshake3 {
   // repeated mux.ProtocolID services = 3;
 
   // we'll have more fields here later.
+  optional string observedAddr = 4;
 }
diff --git a/util/util.go b/util/util.go
index 9ba3d62f7..0076322e2 100644
--- a/util/util.go
+++ b/util/util.go
@@ -4,12 +4,16 @@ import (
 	"errors"
 	"io"
 	"math/rand"
+	"net"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"time"
 
 	ds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore"
+	ma "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr"
+	manet "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr/net"
 	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/mitchellh/go-homedir"
 )
 
@@ -107,3 +111,40 @@ func GetenvBool(name string) bool {
 	v := strings.ToLower(os.Getenv(name))
 	return v == "true" || v == "t" || v == "1"
 }
+
+func IsLoopbackAddr(addr string) bool {
+	return addr == "/ip4/127.0.0.1" || addr == "/ip6/::1"
+}
+
+func GetLocalAddresses() ([]ma.Multiaddr, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	var maddrs []ma.Multiaddr
+	for _, i := range ifaces {
+		addrs, err := i.Addrs()
+		if err != nil {
+			log.Warningf("Skipping addr: %s", err)
+			continue
+		}
+		for _, addr := range addrs {
+			switch v := addr.(type) {
+			case *net.IPNet:
+				maddr, err := manet.FromIP(v.IP)
+				if err != nil {
+					log.Errorf("maddr parsing error: %s", err)
+					continue
+				}
+				if IsLoopbackAddr(maddr.String()) {
+					continue
+				}
+				maddrs = append(maddrs, maddr)
+			default:
+				log.Errorf("Got '%s' type = '%s'", v, reflect.TypeOf(v))
+			}
+		}
+	}
+	return maddrs, nil
+}