diff --git a/src/msg.hpp b/src/msg.hpp
index f2f8fcf6..8c846708 100644
--- a/src/msg.hpp
+++ b/src/msg.hpp
@@ -50,6 +50,7 @@ namespace zmq
         enum
         {
             more = 1,
+            identity = 64,
             shared = 128
         };
 
diff --git a/src/options.cpp b/src/options.cpp
index aa94a218..4db1a6cb 100644
--- a/src/options.cpp
+++ b/src/options.cpp
@@ -46,7 +46,9 @@ zmq::options_t::options_t () :
     ipv4only (1),
     delay_on_close (true),
     delay_on_disconnect (true),
-    filter (false)
+    filter (false),
+    send_identity (false),
+    recv_identity (false)
 {
 }
 
diff --git a/src/options.hpp b/src/options.hpp
index d017c001..bfc9dc79 100644
--- a/src/options.hpp
+++ b/src/options.hpp
@@ -99,6 +99,12 @@ namespace zmq
 
         //  If 1, (X)SUB socket should filter the messages. If 0, it should not.
         bool filter;
+
+        //  Sends identity to all new connections.
+        bool send_identity;
+
+        //  Receivers identity from all new connections.
+        bool recv_identity;
     };
 
 }
diff --git a/src/pipe.cpp b/src/pipe.cpp
index 9f44c948..25dd51cc 100644
--- a/src/pipe.cpp
+++ b/src/pipe.cpp
@@ -65,8 +65,7 @@ zmq::pipe_t::pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
     peer (NULL),
     sink (NULL),
     state (active),
-    delay (delay_),
-    pipe_id (0)
+    delay (delay_)
 {
 }
 
@@ -88,14 +87,14 @@ void zmq::pipe_t::set_event_sink (i_pipe_events *sink_)
     sink = sink_;
 }
 
-void zmq::pipe_t::set_pipe_id (uint32_t id_)
+void zmq::pipe_t::set_identity (const blob_t &identity_)
 {
-    pipe_id = id_;
+    identity = identity_;
 }
 
-uint32_t zmq::pipe_t::get_pipe_id ()
+zmq::blob_t zmq::pipe_t::get_identity ()
 {
-    return pipe_id;
+    return identity;
 }
 
 bool zmq::pipe_t::check_read ()
diff --git a/src/pipe.hpp b/src/pipe.hpp
index 4533e584..75a20210 100644
--- a/src/pipe.hpp
+++ b/src/pipe.hpp
@@ -1,6 +1,7 @@
 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
     Copyright (c) 2007-2009 iMatix Corporation
+    Copyright (c) 2011 VMware, Inc.
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -28,6 +29,7 @@
 #include "object.hpp"
 #include "stdint.hpp"
 #include "array.hpp"
+#include "blob.hpp"
 
 namespace zmq
 {
@@ -71,8 +73,8 @@ namespace zmq
         void set_event_sink (i_pipe_events *sink_);
 
         //  Pipe endpoint can store an opaque ID to be used by its clients.
-        void set_pipe_id (uint32_t id_);
-        uint32_t get_pipe_id ();
+        void set_identity (const blob_t &identity_);
+        blob_t get_identity ();
 
         //  Returns true if there is at least one message to read in the pipe.
         bool check_read ();
@@ -183,8 +185,8 @@ namespace zmq
         //  asks us to.
         bool delay;
 
-        //  Opaque ID. To be used by the clients, not the pipe itself.
-        uint32_t pipe_id;
+        //  Identity of the writer. Used uniquely by the reader side.
+        blob_t identity;
 
         //  Returns true if the message is delimiter; false otherwise.
         static bool is_delimiter (msg_t &msg_);
diff --git a/src/req.cpp b/src/req.cpp
index 40c4765f..3ba1ec01 100644
--- a/src/req.cpp
+++ b/src/req.cpp
@@ -147,23 +147,32 @@ zmq::req_session_t::req_session_t (io_thread_t *io_thread_, bool connect_,
 
 zmq::req_session_t::~req_session_t ()
 {
+    state = options.recv_identity ? identity : bottom;
 }
 
 int zmq::req_session_t::write (msg_t *msg_)
 {
-    if (state == bottom) {
+    switch (state) {
+    case bottom:
         if (msg_->flags () == msg_t::more && msg_->size () == 0) {
             state = body;
             return xreq_session_t::write (msg_);
         }
-    }
-    else {
+        break;
+    case body:
         if (msg_->flags () == msg_t::more)
             return xreq_session_t::write (msg_);
         if (msg_->flags () == 0) {
             state = bottom;
             return xreq_session_t::write (msg_);
         }
+        break;
+    case identity:
+        if (msg_->flags () == 0) {
+            state = bottom;
+            return xreq_session_t::write (msg_);
+        }
+        break;
     }
     errno = EFAULT;
     return -1;
diff --git a/src/req.hpp b/src/req.hpp
index 61066cad..8fae9d40 100644
--- a/src/req.hpp
+++ b/src/req.hpp
@@ -71,6 +71,7 @@ namespace zmq
     private:
 
         enum {
+            identity,
             bottom,
             body
         } state;
diff --git a/src/session_base.cpp b/src/session_base.cpp
index 4c5e5127..f2ee7139 100644
--- a/src/session_base.cpp
+++ b/src/session_base.cpp
@@ -112,7 +112,9 @@ zmq::session_base_t::session_base_t (class io_thread_t *io_thread_,
     engine (NULL),
     socket (socket_),
     io_thread (io_thread_),
-    has_linger_timer (false)
+    has_linger_timer (false),
+    send_identity (options_.send_identity),
+    recv_identity (options_.recv_identity)
 {
     if (protocol_)
         protocol = protocol_;
@@ -146,6 +148,16 @@ void zmq::session_base_t::attach_pipe (pipe_t *pipe_)
 
 int zmq::session_base_t::read (msg_t *msg_)
 {
+    //  First message to send is identity (if required).
+    if (send_identity) {
+        zmq_assert (!(msg_->flags () & msg_t::more));
+        msg_->init_size (options.identity_size);
+        memcpy (msg_->data (), options.identity, options.identity_size);
+        send_identity = false;
+        incomplete_in = false;
+        return 0;
+    }
+
     if (!pipe || !pipe->read (msg_)) {
         errno = EAGAIN;
         return -1;
@@ -157,6 +169,12 @@ int zmq::session_base_t::read (msg_t *msg_)
 
 int zmq::session_base_t::write (msg_t *msg_)
 {
+    //  First message to receive is identity (if required).
+    if (recv_identity) {
+        msg_->set_flags (msg_t::identity);
+        recv_identity = false;
+    }
+
     if (pipe && pipe->write (msg_)) {
         int rc = msg_->init ();
         errno_assert (rc == 0);
diff --git a/src/session_base.hpp b/src/session_base.hpp
index 86a670f8..c89628f7 100644
--- a/src/session_base.hpp
+++ b/src/session_base.hpp
@@ -1,6 +1,7 @@
 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
     Copyright (c) 2007-2009 iMatix Corporation
+    Copyright (c) 2011 VMware, Inc.
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -119,6 +120,10 @@ namespace zmq
         //  True is linger timer is running.
         bool has_linger_timer;
 
+        //  If true, identity is to be sent/recvd from the network.
+        bool send_identity;
+        bool recv_identity;
+
         //  Protocol and address to use when connecting.
         std::string protocol;
         std::string address;
diff --git a/src/socket_base.cpp b/src/socket_base.cpp
index 583818b2..a59ba698 100644
--- a/src/socket_base.cpp
+++ b/src/socket_base.cpp
@@ -845,7 +845,16 @@ void zmq::socket_base_t::terminated (pipe_t *pipe_)
 
 void zmq::socket_base_t::extract_flags (msg_t *msg_)
 {
+    //  Test whether IDENTITY flag is valid for this socket type.
+    if (unlikely (msg_->flags () & msg_t::identity)) {
+        zmq_assert (options.recv_identity);
+printf ("identity recvd\n");
+    }
+  
+
+    //  Remove MORE flag.
     rcvmore = msg_->flags () & msg_t::more ? true : false;
     if (rcvmore)
         msg_->reset_flags (msg_t::more);
 }
+
diff --git a/src/xrep.cpp b/src/xrep.cpp
index 350d7520..ea19e56d 100644
--- a/src/xrep.cpp
+++ b/src/xrep.cpp
@@ -43,6 +43,9 @@ zmq::xrep_t::xrep_t (class ctx_t *parent_, uint32_t tid_) :
     //  all the outstanding requests from that peer.
     //  options.delay_on_disconnect = false;
 
+    options.send_identity = true;
+    options.recv_identity = true;
+
     prefetched_msg.init ();
 }
 
@@ -56,33 +59,22 @@ void zmq::xrep_t::xattach_pipe (pipe_t *pipe_)
 {
     zmq_assert (pipe_);
 
-    //  Generate a new peer ID. Take care to avoid duplicates.
-    outpipes_t::iterator it = outpipes.lower_bound (next_peer_id);
-    if (!outpipes.empty ()) {
-        while (true) {
-            if (it == outpipes.end ())
-                it = outpipes.begin ();
-            if (it->first != next_peer_id)
-                break;
-            ++next_peer_id;
-            ++it;
-        }
-    }
+    //  Generate a new unique peer identity.
+    unsigned char buf [5];
+    buf [0] = 0;
+    put_uint32 (buf + 1, next_peer_id);
+    blob_t identity (buf, 5);
+    ++next_peer_id;
 
     //  Add the pipe to the map out outbound pipes.
     outpipe_t outpipe = {pipe_, true};
     bool ok = outpipes.insert (outpipes_t::value_type (
-        next_peer_id, outpipe)).second;
+        identity, outpipe)).second;
     zmq_assert (ok);
 
     //  Add the pipe to the list of inbound pipes.
-    pipe_->set_pipe_id (next_peer_id);
-    fq.attach (pipe_);
-
-    //  Advance next peer ID so that if new connection is dropped shortly after
-    //  its creation we don't accidentally get two subsequent peers with
-    //  the same ID.
-    ++next_peer_id;
+    pipe_->set_identity (identity);
+    fq.attach (pipe_);    
 }
 
 void zmq::xrep_t::xterminated (pipe_t *pipe_)
@@ -133,26 +125,25 @@ int zmq::xrep_t::xsend (msg_t *msg_, int flags_)
 
             more_out = true;
 
-            //  Find the pipe associated with the peer ID stored in the prefix.
+            //  Find the pipe associated with the identity stored in the prefix.
             //  If there's no such pipe just silently ignore the message.
-            if (msg_->size () == 4) {
-                uint32_t peer_id = get_uint32 ((unsigned char*) msg_->data ());
-                outpipes_t::iterator it = outpipes.find (peer_id);
+            blob_t identity ((unsigned char*) msg_->data (), msg_->size ());
+            outpipes_t::iterator it = outpipes.find (identity);
 
-                if (it != outpipes.end ()) {
-                    current_out = it->second.pipe;
-                    msg_t empty;
-                    int rc = empty.init ();
-                    errno_assert (rc == 0);
-                    if (!current_out->check_write (&empty)) {
-                        it->second.active = false;
-                        more_out = false;
-                        current_out = NULL;
-                    }
-                    rc = empty.close ();
-                    errno_assert (rc == 0);
+            if (it != outpipes.end ()) {
+                current_out = it->second.pipe;
+                msg_t empty;
+                int rc = empty.init ();
+                errno_assert (rc == 0);
+                if (!current_out->check_write (&empty)) {
+                    it->second.active = false;
+                    more_out = false;
+                    current_out = NULL;
                 }
+                rc = empty.close ();
+                errno_assert (rc == 0);
             }
+
         }
 
         int rc = msg_->close ();
@@ -204,6 +195,37 @@ int zmq::xrep_t::xrecv (msg_t *msg_, int flags_)
     if (rc != 0)
         return -1;
 
+    //  If identity is received, change the key assigned to the pipe.
+    if (unlikely (msg_->flags () & msg_t::identity)) {
+        zmq_assert (!more_in);
+
+        //  Empty identity means we can preserve the auto-generated identity.
+        if (msg_->size () != 0) {
+
+            //  Actual change of the identity.
+            outpipes_t::iterator it = outpipes.begin ();
+            while (it != outpipes.end ()) {
+                if (it->second.pipe == pipe) {
+                    blob_t identity ((unsigned char*) msg_->data (),
+                        msg_->size ());
+                    pipe->set_identity (identity);
+                    outpipes.erase (it);
+                    outpipe_t outpipe = {pipe, true};
+                    outpipes.insert (outpipes_t::value_type (identity,
+                        outpipe));
+                    break;
+                }
+                ++it;
+            }
+            zmq_assert (it != outpipes.end ());
+        }
+
+        //  After processing the identity, try to get the next message.
+        rc = fq.recvpipe (msg_, flags_, &pipe);
+        if (rc != 0)
+            return -1;
+    }
+
     //  If we are in the middle of reading a message, just return the next part.
     if (more_in) {
         more_in = msg_->flags () & msg_t::more ? true : false;
@@ -217,9 +239,11 @@ int zmq::xrep_t::xrecv (msg_t *msg_, int flags_)
     prefetched = true;
     rc = msg_->close ();
     errno_assert (rc == 0);
-    rc = msg_->init_size (4);
+
+    blob_t identity = pipe->get_identity ();
+    rc = msg_->init_size (identity.size ());
     errno_assert (rc == 0);
-    put_uint32 ((unsigned char*) msg_->data (), pipe->get_pipe_id ());
+    memcpy (msg_->data (), identity.data (), identity.size ());
     msg_->set_flags (msg_t::more);
     return 0;
 }
diff --git a/src/xrep.hpp b/src/xrep.hpp
index 8cec683d..fc02b11e 100644
--- a/src/xrep.hpp
+++ b/src/xrep.hpp
@@ -1,6 +1,7 @@
 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
     Copyright (c) 2011 iMatix Corporation
+    Copyright (c) 2011 VMware, Inc.
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -27,6 +28,7 @@
 #include "socket_base.hpp"
 #include "session_base.hpp"
 #include "stdint.hpp"
+#include "blob.hpp"
 #include "msg.hpp"
 #include "fq.hpp"
 
@@ -78,7 +80,7 @@ namespace zmq
         };
 
         //  Outbound pipes indexed by the peer IDs.
-        typedef std::map <uint32_t, outpipe_t> outpipes_t;
+        typedef std::map <blob_t, outpipe_t> outpipes_t;
         outpipes_t outpipes;
 
         //  The pipe we are currently writing to.
diff --git a/src/xreq.cpp b/src/xreq.cpp
index f4f962f4..91317f79 100644
--- a/src/xreq.cpp
+++ b/src/xreq.cpp
@@ -1,5 +1,6 @@
 /*
     Copyright (c) 2009-2011 250bpm s.r.o.
+    Copyright (c) 2011 VMware, Inc.
     Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
 
     This file is part of 0MQ.
@@ -32,6 +33,9 @@ zmq::xreq_t::xreq_t (class ctx_t *parent_, uint32_t tid_) :
     //  If the socket is closing we can drop all the outbound requests. There'll
     //  be noone to receive the replies anyway.
     //  options.delay_on_close = false;
+
+    options.send_identity = true;
+    options.recv_identity = true;
 }
 
 zmq::xreq_t::~xreq_t ()
@@ -52,7 +56,15 @@ int zmq::xreq_t::xsend (msg_t *msg_, int flags_)
 
 int zmq::xreq_t::xrecv (msg_t *msg_, int flags_)
 {
-    return fq.recv (msg_, flags_);
+    //  XREQ socket doesn't use identities. We can safely drop it and 
+    while (true) {
+        int rc = fq.recv (msg_, flags_);
+        if (rc != 0)
+            return rc;
+        if (likely (!(msg_->flags () & msg_t::identity)))
+            break;
+    }
+    return 0;
 }
 
 bool zmq::xreq_t::xhas_in ()
diff --git a/tests/test_invalid_rep.cpp b/tests/test_invalid_rep.cpp
index ada7ee11..9c77cc4b 100644
--- a/tests/test_invalid_rep.cpp
+++ b/tests/test_invalid_rep.cpp
@@ -25,7 +25,7 @@
 
 int main (int argc, char *argv [])
 {
-    fprintf (stderr, "test_pair_inproc running...\n");
+    fprintf (stderr, "test_invalid_rep running...\n");
 
     //  Create REQ/XREP wiring.
     void *ctx = zmq_init (1);
@@ -49,23 +49,24 @@ int main (int argc, char *argv [])
     assert (rc == 1);
 
     //  Receive the request.
-    char addr [4];
+    char addr [32];
+    int addr_size;
     char bottom [1];
     char body [1];
-    rc = zmq_recv (xrep_socket, addr, sizeof (addr), 0);
-    assert (rc == 4);
+    addr_size = zmq_recv (xrep_socket, addr, sizeof (addr), 0);
+    assert (addr_size >= 0);
     rc = zmq_recv (xrep_socket, bottom, sizeof (bottom), 0);
     assert (rc == 0);
     rc = zmq_recv (xrep_socket, body, sizeof (body), 0);
     assert (rc == 1);
 
     //  Send invalid reply.
-    rc = zmq_send (xrep_socket, addr, 4, 0);
-    assert (rc == 4);
+    rc = zmq_send (xrep_socket, addr, addr_size, 0);
+    assert (rc == addr_size);
 
     //  Send valid reply.
-    rc = zmq_send (xrep_socket, addr, 4, ZMQ_SNDMORE);
-    assert (rc == 4);
+    rc = zmq_send (xrep_socket, addr, addr_size, ZMQ_SNDMORE);
+    assert (rc == addr_size);
     rc = zmq_send (xrep_socket, bottom, 0, ZMQ_SNDMORE);
     assert (rc == 0);
     rc = zmq_send (xrep_socket, "b", 1, 0);