diff --git a/src/ca/cac.cpp b/src/ca/cac.cpp
index 835a1689d..fbcd57b21 100644
--- a/src/ca/cac.cpp
+++ b/src/ca/cac.cpp
@@ -65,7 +65,8 @@ const cac::pProtoStubTCP cac::tcpJumpTableCAC [] =
     &cac::badTCPRespAction,
     &cac::badTCPRespAction,
     &cac::badTCPRespAction,
-    &cac::badTCPRespAction,
+    // legacy CA_PROTO_READ_SYNC used as an echo with legacy server
+    &cac::echoRespAction, 
     &cac::exceptionRespAction,
     &cac::clearChannelRespAction,
     &cac::badTCPRespAction,
@@ -467,7 +468,7 @@ cacChannel & cac::createChannel (
 }
 
 void cac::transferChanToVirtCircuit ( 
-    epicsGuard < epicsMutex > & cbGuard, unsigned cid, unsigned sid, // X aCC 431
+    unsigned cid, unsigned sid, // X aCC 431
     ca_uint16_t typeCode, arrayElementCount count, 
     unsigned minorVersionNumber, const osiSockAddr & addr,
     const epicsTime & currentTime )
@@ -549,12 +550,7 @@ void cac::transferChanToVirtCircuit (
     pChan->getPIIU(guard)->uninstallChanDueToSuccessfulSearchResponse ( 
         guard, *pChan, currentTime );
     piiu->installChannel ( 
-        cbGuard, guard, *pChan, sid, typeCode, count );
-
-    if ( ! piiu->ca_v42_ok ( guard ) ) {
-        // connect to old server with lock applied
-        pChan->connect ( cbGuard, guard );
-    }
+        guard, *pChan, sid, typeCode, count );
 
     if ( newIIU ) {
         piiu->start ( guard );
diff --git a/src/ca/cac.h b/src/ca/cac.h
index 9c4c471a7..c4cf59a85 100644
--- a/src/ca/cac.h
+++ b/src/ca/cac.h
@@ -127,7 +127,6 @@ public:
 
     // channel routines
     void transferChanToVirtCircuit ( 
-        epicsGuard < epicsMutex > &,
         unsigned cid, unsigned sid, 
         ca_uint16_t typeCode, arrayElementCount count, 
         unsigned minorVersionNumber, const osiSockAddr &,
diff --git a/src/ca/nciu.cpp b/src/ca/nciu.cpp
index ba08015b4..9d45584c2 100644
--- a/src/ca/nciu.cpp
+++ b/src/ca/nciu.cpp
@@ -476,12 +476,7 @@ double nciu::receiveWatchdogDelay (
 bool nciu::connected ( epicsGuard < epicsMutex > & guard ) const
 {
     guard.assertIdenticalMutex ( this->cacCtx.mutexRef () );
-    if ( this->piiu->ca_v42_ok ( guard ) ) {
-        return this->channelNode::isConnectedAtOrAfterV42 ( guard );
-    }
-    else {
-        return this->channelNode::isConnectedBeforeV42 ( guard );
-    }
+    return this->channelNode::isConnected ( guard );
 }
 
 void nciu::show ( unsigned level ) const
diff --git a/src/ca/nciu.h b/src/ca/nciu.h
index 0890d6b89..56be56964 100644
--- a/src/ca/nciu.h
+++ b/src/ca/nciu.h
@@ -56,9 +56,8 @@ class channelNode : public tsDLNode < class nciu >
 {
 protected:
     channelNode ();
-    bool isConnectedAtOrAfterV42 ( epicsGuard < epicsMutex > & ) const;
-    bool isConnectedBeforeV42 ( epicsGuard < epicsMutex > & ) const;
     bool isInstalledInServer ( epicsGuard < epicsMutex > & ) const;
+    bool isConnected ( epicsGuard < epicsMutex > & ) const;
     static unsigned getMaxSearchTimerCount ();
 private:
     enum channelState {
@@ -106,6 +105,7 @@ private:
         cs_searchRespPending17,
         cs_createReqPend,
         cs_createRespPend,
+        cs_v42ConnCallbackPend,
         cs_subscripReqPend,
         cs_connected,
         cs_unrespCircuit,
@@ -354,7 +354,7 @@ inline channelNode::channelNode () :
 {
 }
 
-inline bool channelNode::isConnectedAtOrAfterV42 ( epicsGuard < epicsMutex > & ) const
+inline bool channelNode::isConnected ( epicsGuard < epicsMutex > & ) const
 {
     return 
         this->listMember == cs_connected || 
@@ -362,15 +362,6 @@ inline bool channelNode::isConnectedAtOrAfterV42 ( epicsGuard < epicsMutex > & )
         this->listMember == cs_subscripUpdateReqPend;
 }
 
-inline bool channelNode::isConnectedBeforeV42 ( epicsGuard < epicsMutex > & ) const
-{
-    return 
-        this->listMember == cs_connected || 
-        this->listMember == cs_subscripReqPend ||
-        this->listMember == cs_subscripUpdateReqPend ||
-        this->listMember == cs_createReqPend;
-}
-
 inline bool channelNode::isInstalledInServer ( epicsGuard < epicsMutex > & ) const
 {
     return 
diff --git a/src/ca/tcpiiu.cpp b/src/ca/tcpiiu.cpp
index 96231edd2..09c9969fa 100644
--- a/src/ca/tcpiiu.cpp
+++ b/src/ca/tcpiiu.cpp
@@ -109,27 +109,30 @@ void tcpSendThread::run ()
             }
 
             if ( echoLaborNeeded ) {
-                if ( CA_V43 ( this->iiu.minorProtocolVersion ) ) {
-                    this->iiu.echoRequest ( guard );
-                }
-                else {
-                    this->iiu.versionMessage ( guard, this->iiu.priority() );
-                }
+                this->iiu.echoRequest ( guard );
             }
 
             while ( nciu * pChan = this->iiu.createReqPend.get () ) {
                 this->iiu.createChannelRequest ( *pChan, guard );
+
                 if ( CA_V42 ( this->iiu.minorProtocolVersion ) ) {
                     this->iiu.createRespPend.add ( *pChan );
                     pChan->channelNode::listMember = 
                         channelNode::cs_createRespPend;
                 }
                 else {
-                    this->iiu.subscripReqPend.add ( *pChan );
+                    // This wakes up the resp thread so that it can call
+                    // the connect callback. This isnt maximally efficent
+                    // but it has the excellent side effect of not requiring
+                    // that the UDP thread take the callback lock. There are
+                    // almost no V42 servers left at this point.
+                    this->iiu.v42ConnCallbackPend.add ( *pChan );
                     pChan->channelNode::listMember = 
-                        channelNode::cs_subscripReqPend;
+                        channelNode::cs_v42ConnCallbackPend;
+                    this->iiu.echoRequestPending = true;
+                    laborPending = true;
                 }
-
+                
                 if ( this->iiu.sendQue.flushBlockThreshold ( 0u ) ) {
                     laborPending = true;
                     break;
@@ -494,6 +497,13 @@ void tcpRecvThread::run ()
                 callbackManager mgr ( this->ctxNotify, this->cbMutex );
 
                 epicsGuard < epicsMutex > guard ( this->iiu.mutex );
+                
+                // route legacy V42 channel connect through the recv thread -
+                // the only thread that should be taking the callback lock
+                while ( nciu * pChan = this->iiu.v42ConnCallbackPend.first () ) {
+                    this->iiu.connectNotify ( guard, *pChan );
+                    pChan->connect ( mgr.cbGuard, guard );
+                }
 
                 // force the receive watchdog to be reset every 5 frames
                 unsigned contiguousFrameCount = 0;
@@ -1062,6 +1072,14 @@ void tcpiiu::show ( unsigned level ) const
                 pChan++;
             }
         }
+        if ( this->v42ConnCallbackPend.count () ) {
+            ::printf ( "V42 Conn Callback pending channels\n" );
+            tsDLIterConst < nciu > pChan = this->v42ConnCallbackPend.firstIter ();
+	        while ( pChan.valid () ) {
+                pChan->show ( level - 2u );
+                pChan++;
+            }
+        }
         if ( this->subscripReqPend.count () ) {
             ::printf ( "Subscription request pending channels\n" );
             tsDLIterConst < nciu > pChan = this->subscripReqPend.firstIter ();
@@ -1348,13 +1366,19 @@ void tcpiiu::versionMessage ( epicsGuard < epicsMutex > & guard, // X aCC 431
 void tcpiiu::echoRequest ( epicsGuard < epicsMutex > & guard ) // X aCC 431
 {
     guard.assertIdenticalMutex ( this->mutex );
+    
+    int command = CA_PROTO_ECHO;
+    if ( ! CA_V43 ( this->minorProtocolVersion ) ) {
+        // we fake an echo to early server using a read sync
+        command = CA_PROTO_READ_SYNC;
+    }
 
     if ( this->sendQue.flushEarlyThreshold ( 16u ) ) {
         this->flushRequest ( guard );
     }
     comQueSendMsgMinder minder ( this->sendQue, guard );
     this->sendQue.insertRequestHeader ( 
-        CA_PROTO_ECHO, 0u, 
+        command, 0u, 
         0u, 0u, 0u, 0u, 
         CA_V49 ( this->minorProtocolVersion ) );
     minder.commit ();
@@ -1756,6 +1780,12 @@ void tcpiiu::disconnectAllChannels (
             pChan->getSID(guard), pChan->getCID(guard) );
         discIIU.installDisconnectedChannel ( guard, *pChan );
     }
+    
+    while ( nciu * pChan = this->v42ConnCallbackPend.get () ) {
+        this->clearChannelRequest ( guard, 
+            pChan->getSID(guard), pChan->getCID(guard) );
+        discIIU.installDisconnectedChannel ( guard, *pChan );
+    }
 
     while ( nciu * pChan = this->subscripReqPend.get () ) {
         pChan->disconnectAllIO ( cbGuard, guard );
@@ -1798,6 +1828,13 @@ void tcpiiu::unlinkAllChannels (
             pChan->getSID(guard), pChan->getCID(guard) );
         pChan->serviceShutdownNotify ( cbGuard, guard );
     }
+    
+    while ( nciu * pChan = this->v42ConnCallbackPend.get () ) {
+        pChan->disconnectAllIO ( cbGuard, guard );
+        this->clearChannelRequest ( guard, 
+            pChan->getSID(guard), pChan->getCID(guard) );
+        pChan->serviceShutdownNotify ( cbGuard, guard );
+    }
 
     while ( nciu * pChan = this->subscripReqPend.get () ) {
         pChan->disconnectAllIO ( cbGuard, guard );
@@ -1820,7 +1857,6 @@ void tcpiiu::unlinkAllChannels (
 }
 
 void tcpiiu::installChannel ( 
-    epicsGuard < epicsMutex > & /* cbGuard */,
     epicsGuard < epicsMutex > & guard, 
     nciu & chan, unsigned sidIn, 
     ca_uint16_t typeIn, arrayElementCount countIn )
@@ -1861,6 +1897,11 @@ void tcpiiu::connectNotify (
         this->subscripReqPend.add ( chan );
         chan.channelNode::listMember = channelNode::cs_subscripReqPend;
     }
+    else if ( chan.channelNode::listMember == channelNode::cs_v42ConnCallbackPend ) {
+        this->v42ConnCallbackPend.remove ( chan );
+        this->subscripReqPend.add ( chan );
+        chan.channelNode::listMember = channelNode::cs_subscripReqPend;
+    }
     // the TCP send thread is awakened by its receive thread whenever the receive thread
     // is about to block if this->subscripReqPend has items in it
 }
@@ -1877,6 +1918,9 @@ void tcpiiu::uninstallChan (
     case channelNode::cs_createRespPend:
         this->createRespPend.remove ( chan );
         break;
+    case channelNode::cs_v42ConnCallbackPend:
+        this->v42ConnCallbackPend.remove ( chan );
+        break;
     case channelNode::cs_subscripReqPend:
         this->subscripReqPend.remove ( chan );
         break;
diff --git a/src/ca/udpiiu.cpp b/src/ca/udpiiu.cpp
index f8413f0a7..5a0d3ccdd 100644
--- a/src/ca/udpiiu.cpp
+++ b/src/ca/udpiiu.cpp
@@ -235,7 +235,7 @@ udpiiu::udpiiu (
      */
     ellInit ( & this->dest );    // X aCC 392
     configureChannelAccessAddressList ( & this->dest, this->sock, this->serverPort );
-  
+    
     caStartRepeaterIfNotInstalled ( this->repeaterPort );
 
     this->pushVersionMsg ();
@@ -338,7 +338,7 @@ void udpRecvThread::show ( unsigned /* level */ ) const
 void udpRecvThread::run ()
 {
     epicsThreadPrivateSet ( caClientCallbackThreadId, &this->iiu );
-
+    
     if ( ellCount ( & this->iiu.dest ) == 0 ) { // X aCC 392
         callbackManager mgr ( this->ctxNotify, this->cbMutex );
         epicsGuard < epicsMutex > guard ( this->iiu.cacMutex );
@@ -353,8 +353,6 @@ void udpRecvThread::run ()
             this->iiu.recvBuf, sizeof ( this->iiu.recvBuf ), 0,
             & src.sa, & src_size );
 
-        callbackManager mgr ( this->ctxNotify, this->cbMutex );
-
         if ( status <= 0 ) {
 
             if ( status < 0 ) {
@@ -379,7 +377,7 @@ void udpRecvThread::run ()
             }
         }
         else if ( status > 0 ) {
-            this->iiu.postMsg ( mgr.cbGuard, src, this->iiu.recvBuf, 
+            this->iiu.postMsg ( src, this->iiu.recvBuf, 
                 (arrayElementCount) status, epicsTime::getCurrent() );
         }
 
@@ -586,19 +584,18 @@ void epicsShareAPI caStartRepeaterIfNotInstalled ( unsigned repeaterPort )
 }
 
 bool udpiiu::badUDPRespAction ( 
-    epicsGuard < epicsMutex > & guard, const caHdr &msg, 
-    const osiSockAddr &netAddr, const epicsTime &currentTime )
+    const caHdr &msg, const osiSockAddr &netAddr, const epicsTime &currentTime )
 {
     char buf[64];
     sockAddrToDottedIP ( &netAddr.sa, buf, sizeof ( buf ) );
     char date[64];
     currentTime.strftime ( date, sizeof ( date ), "%a %b %d %Y %H:%M:%S");
-    this->printf ( guard, "CAC: Undecipherable ( bad msg code %u ) UDP message from %s at %s\n", 
+    errlogPrintf ( "CAC: Undecipherable ( bad msg code %u ) UDP message from %s at %s\n", 
                 msg.m_cmmd, buf, date );
     return false;
 }
 
-bool udpiiu::versionAction ( epicsGuard < epicsMutex > &,
+bool udpiiu::versionAction ( 
     const caHdr & hdr, const osiSockAddr &, const epicsTime & /* currentTime */ )
 {
     epicsGuard < epicsMutex > guard ( this->cacMutex );
@@ -613,7 +610,7 @@ bool udpiiu::versionAction ( epicsGuard < epicsMutex > &,
 }
 
 bool udpiiu::searchRespAction ( // X aCC 361
-        epicsGuard < epicsMutex > & cbGuard, const caHdr &msg,
+        const caHdr &msg,
         const osiSockAddr &  addr, const epicsTime & currentTime )
 {
     if ( addr.sa.sa_family != AF_INET ) {
@@ -666,12 +663,12 @@ bool udpiiu::searchRespAction ( // X aCC 361
 
     if ( CA_V42 ( minorVersion ) ) {
        this->cacRef.transferChanToVirtCircuit 
-            ( cbGuard, msg.m_available, msg.m_cid, 0xffff, 
+            ( msg.m_available, msg.m_cid, 0xffff, 
                 0, minorVersion, serverAddr, currentTime );
     }
     else {
         this->cacRef.transferChanToVirtCircuit 
-            ( cbGuard, msg.m_available, msg.m_cid, msg.m_dataType, 
+            ( msg.m_available, msg.m_cid, msg.m_dataType, 
                 msg.m_count, minorVersion, serverAddr, currentTime );
     }
 
@@ -679,7 +676,7 @@ bool udpiiu::searchRespAction ( // X aCC 361
 }
 
 bool udpiiu::beaconAction ( 
-    epicsGuard < epicsMutex > &, const caHdr & msg, 
+    const caHdr & msg, 
     const osiSockAddr & net_addr, const epicsTime & currentTime )
 {
     struct sockaddr_in ina;
@@ -724,7 +721,7 @@ bool udpiiu::beaconAction (
 }
 
 bool udpiiu::repeaterAckAction ( 
-    epicsGuard < epicsMutex > & /* cbGuard */, const caHdr &,  
+    const caHdr &,  
     const osiSockAddr &, const epicsTime &)
 {
     this->repeaterSubscribeTmr.confirmNotify ();
@@ -732,14 +729,14 @@ bool udpiiu::repeaterAckAction (
 }
 
 bool udpiiu::notHereRespAction ( 
-    epicsGuard < epicsMutex > &, const caHdr &,  
+    const caHdr &,  
         const osiSockAddr &, const epicsTime & )
 {
     return true;
 }
 
 bool udpiiu::exceptionRespAction ( 
-    epicsGuard < epicsMutex > & cbGuard, const caHdr &msg, 
+    const caHdr &msg, 
     const osiSockAddr & net_addr, const epicsTime & currentTime )
 {
     const caHdr &reqMsg = * ( &msg + 1 );
@@ -749,13 +746,13 @@ bool udpiiu::exceptionRespAction (
     currentTime.strftime ( date, sizeof ( date ), "%a %b %d %Y %H:%M:%S");
 
     if ( msg.m_postsize > sizeof ( caHdr ) ){
-        this->cacRef.printf ( cbGuard, 
+        errlogPrintf ( 
             "error condition \"%s\" detected by %s with context \"%s\" at %s\n", 
             ca_message ( msg.m_available ), 
             name, reinterpret_cast <const char *> ( &reqMsg + 1 ), date );
     }
     else{
-        this->cacRef.printf ( cbGuard,
+        errlogPrintf ( 
             "error condition \"%s\" detected by %s at %s\n", 
             ca_message ( msg.m_available ), name, date );
     }
@@ -763,7 +760,7 @@ bool udpiiu::exceptionRespAction (
     return true;
 }
 
-void udpiiu::postMsg ( epicsGuard < epicsMutex > & cbGuard, 
+void udpiiu::postMsg ( 
               const osiSockAddr & net_addr, 
               char * pInBuf, arrayElementCount blockSize,
               const epicsTime & currentTime )
@@ -779,7 +776,7 @@ void udpiiu::postMsg ( epicsGuard < epicsMutex > & cbGuard,
         if ( blockSize < sizeof ( *pCurMsg ) ) {
             char buf[64];
             sockAddrToDottedIP ( &net_addr.sa, buf, sizeof ( buf ) );
-            this->printf ( cbGuard,
+            errlogPrintf ( 
                 "%s: Undecipherable (too small) UDP msg from %s ignored\n", 
                     __FILE__,  buf );
             return;
@@ -816,7 +813,7 @@ void udpiiu::postMsg ( epicsGuard < epicsMutex > & cbGuard,
         if ( size > blockSize ) {
             char buf[64];
             sockAddrToDottedIP ( &net_addr.sa, buf, sizeof ( buf ) );
-            this->printf ( cbGuard,
+            errlogPrintf ( 
                 "%s: Undecipherable (payload too small) UDP msg from %s ignored\n", 
                 __FILE__, buf );
             return;
@@ -832,11 +829,11 @@ void udpiiu::postMsg ( epicsGuard < epicsMutex > & cbGuard,
         else {
             pStub = &udpiiu::badUDPRespAction;
         }
-        bool success = ( this->*pStub ) ( cbGuard, *pCurMsg, net_addr, currentTime );
+        bool success = ( this->*pStub ) ( *pCurMsg, net_addr, currentTime );
         if ( ! success ) {
             char buf[256];
             sockAddrToDottedIP ( &net_addr.sa, buf, sizeof ( buf ) );
-            this->printf ( cbGuard, "CAC: Undecipherable UDP message from %s\n", buf );
+            errlogPrintf ( "CAC: Undecipherable UDP message from %s\n", buf );
             return;
         }
 
diff --git a/src/ca/udpiiu.h b/src/ca/udpiiu.h
index aa5256efd..639cebcfe 100644
--- a/src/ca/udpiiu.h
+++ b/src/ca/udpiiu.h
@@ -137,7 +137,7 @@ private:
 
     bool wakeupMsg ();
 
-    void postMsg ( epicsGuard < epicsMutex > & cbGuard, 
+    void postMsg ( 
             const osiSockAddr & net_addr, 
             char *pInBuf, arrayElementCount blockSize,
             const epicsTime &currenTime );
@@ -147,7 +147,7 @@ private:
         ca_uint16_t extsize);
 
     typedef bool ( udpiiu::*pProtoStubUDP ) ( 
-        epicsGuard < epicsMutex > &, const caHdr &, 
+        const caHdr &, 
         const osiSockAddr &, const epicsTime & );
 
     // UDP protocol dispatch table
@@ -155,25 +155,25 @@ private:
 
     // UDP protocol stubs
     bool versionAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &, 
+        const caHdr &, 
         const osiSockAddr &, const epicsTime & );
     bool badUDPRespAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &netAddr, const epicsTime & );
     bool searchRespAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &net_addr, const epicsTime & );
     bool exceptionRespAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &net_addr, const epicsTime & );
     bool beaconAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &net_addr, const epicsTime & );
     bool notHereRespAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &net_addr, const epicsTime & );
     bool repeaterAckAction ( 
-        epicsGuard < epicsMutex > &, const caHdr &msg, 
+        const caHdr &msg, 
         const osiSockAddr &net_addr, const epicsTime & );
 
     // netiiu stubs
diff --git a/src/ca/virtualCircuit.h b/src/ca/virtualCircuit.h
index 414d33d96..7532ce181 100644
--- a/src/ca/virtualCircuit.h
+++ b/src/ca/virtualCircuit.h
@@ -167,7 +167,7 @@ public:
     void unlinkAllChannels (
         epicsGuard < epicsMutex > & cbGuard, 
         epicsGuard < epicsMutex > & guard );
-    void installChannel ( epicsGuard < epicsMutex > &,
+    void installChannel ( 
         epicsGuard < epicsMutex > &, nciu & chan, 
         unsigned sidIn, ca_uint16_t typeIn, arrayElementCount countIn );
     void uninstallChan ( 
@@ -193,6 +193,7 @@ private:
     // protected by the callback mutex
     tsDLList < nciu > createReqPend;
     tsDLList < nciu > createRespPend;
+    tsDLList < nciu > v42ConnCallbackPend;
     tsDLList < nciu > subscripReqPend;
     tsDLList < nciu > connectedList;
     tsDLList < nciu > unrespCircuit;