diff --git a/src/ioc/db/dbCAC.h b/src/ioc/db/dbCAC.h
index ad3d0287b..82b20b619 100644
--- a/src/ioc/db/dbCAC.h
+++ b/src/ioc/db/dbCAC.h
@@ -201,6 +201,7 @@ private:
     cacContextNotify & notify;
     epics_auto_ptr < cacContext > pNetContext;
     char * pStateNotifyCache;
+    bool isolated;
 
     cacChannel & createChannel (
         epicsGuard < epicsMutex > &,
diff --git a/src/ioc/db/dbCa.c b/src/ioc/db/dbCa.c
index 984b59f13..029037f0e 100644
--- a/src/ioc/db/dbCa.c
+++ b/src/ioc/db/dbCa.c
@@ -52,8 +52,11 @@
 #include "link.h"
 #include "recSup.h"
 
+/* defined in dbContext.cpp
+ * Setup local CA access
+ */
 extern void dbServiceIOInit();
-
+extern int dbServiceIsolate;
 
 static ELLLIST workList = ELLLIST_INIT;    /* Work list for dbCaTask */
 static epicsMutexId workListLock; /*Mutual exclusions semaphores for workList*/
@@ -224,25 +227,16 @@ void dbCaShutdown(void)
     }
 }
 
-static void dbCaExit(void *arg)
+static void dbCaLinkInitImpl(int isolate)
 {
-    dbCaShutdown();
-}
+    dbServiceIsolate = isolate;
+    dbServiceIOInit();
 
-void dbCaLinkInitIsolated(void)
-{
     if (!workListLock)
         workListLock = epicsMutexMustCreate();
     if (!workListEvent)
         workListEvent = epicsEventMustCreate(epicsEventEmpty);
-    dbCaCtl = ctlExit;
-    epicsAtExit(dbCaExit, NULL);
-}
 
-void dbCaLinkInit(void)
-{
-    dbServiceIOInit();
-    dbCaLinkInitIsolated();
     startStopEvent = epicsEventMustCreate(epicsEventEmpty);
     dbCaCtl = ctlPause;
 
@@ -252,6 +246,16 @@ void dbCaLinkInit(void)
     epicsEventMustWait(startStopEvent);
 }
 
+void dbCaLinkInitIsolated(void)
+{
+    dbCaLinkInitImpl(1);
+}
+
+void dbCaLinkInit(void)
+{
+    dbCaLinkInitImpl(0);
+}
+
 void dbCaRun(void)
 {
     if (dbCaCtl == ctlPause) {
diff --git a/src/ioc/db/dbChannelNOOP.h b/src/ioc/db/dbChannelNOOP.h
new file mode 100644
index 000000000..d48540d88
--- /dev/null
+++ b/src/ioc/db/dbChannelNOOP.h
@@ -0,0 +1,118 @@
+#ifndef DBCHANNELNOOP_H
+#define DBCHANNELNOOP_H
+
+#include <string.h>
+#include <string>
+
+#include "cacIO.h"
+#include "caerr.h"
+
+/** @brief A channel which never connects
+ *
+ * Used when dbCa is placed in isolated mode for unittests
+ */
+class dbChannelNOOP : public cacChannel
+{
+    std::string myname;
+public:
+    dbChannelNOOP(const char *name, cacChannelNotify &notify)
+        :cacChannel(notify)
+        ,myname(name)
+    {}
+
+    virtual void destroy (
+            CallbackGuard & /*callbackGuard*/,
+            epicsGuard < epicsMutex > & /*mutualExclusionGuard*/ )
+    {
+        delete this; // goodbye cruel world
+    }
+
+    virtual unsigned getName (
+            epicsGuard < epicsMutex > &,
+            char * pBuf, unsigned bufLen ) const throw ()
+    {
+        const char* name = myname.c_str();
+        if(bufLen>myname.size()+1) {
+            bufLen=myname.size()+1;
+        }
+        memcpy(pBuf, name, bufLen);
+        pBuf[--bufLen] = '\0';
+        return bufLen;
+    }
+
+    // !! deprecated, avoid use  !!
+    virtual const char * pName (
+            epicsGuard < epicsMutex > & guard ) const throw ()
+    {return myname.c_str();}
+
+    virtual void show (
+            epicsGuard < epicsMutex > &,
+            unsigned level ) const
+    {}
+
+    virtual void initiateConnect (
+            epicsGuard < epicsMutex > & )
+    {}
+
+    virtual unsigned requestMessageBytesPending (
+            epicsGuard < epicsMutex > & /*mutualExclusionGuard*/ )
+    {return 0;}
+
+    virtual void flush (
+            epicsGuard < epicsMutex > & /*mutualExclusionGuard*/ )
+    {}
+
+    virtual ioStatus read (
+            epicsGuard < epicsMutex > &mut,
+            unsigned type, arrayElementCount count,
+            cacReadNotify &notify, ioid * = 0 )
+    {
+        notify.exception(mut, ECA_NORDACCESS, "dbChannelNOOP", type, count);
+        return iosSynch;
+    }
+
+    virtual void write (
+            epicsGuard < epicsMutex > &,
+            unsigned type, arrayElementCount count,
+            const void *pValue )
+    {}
+
+    virtual ioStatus write (
+            epicsGuard < epicsMutex > &mut,
+            unsigned type, arrayElementCount count,
+            const void */*pValue*/, cacWriteNotify & notify, ioid * = 0 )
+    {
+        notify.exception(mut, ECA_NOWTACCESS, "dbChannelNOOP", type, count);
+        return iosSynch;
+    }
+
+    virtual void subscribe (
+            epicsGuard < epicsMutex > &mut, unsigned type,
+            arrayElementCount count, unsigned /*mask*/, cacStateNotify & notify,
+            ioid * = 0 )
+    {
+        // should never subscribe
+        notify.exception(mut, ECA_BADMASK, "dbChannelNOOP", type, count);
+    }
+
+    virtual void ioCancel (
+            CallbackGuard & callbackGuard,
+            epicsGuard < epicsMutex > & mutualExclusionGuard,
+            const ioid & )
+    {}
+
+    virtual void ioShow (
+            epicsGuard < epicsMutex > &,
+            const ioid &, unsigned level ) const
+    {}
+
+    virtual short nativeType (
+            epicsGuard < epicsMutex > & ) const
+    {return 0;} // DBR_STRING
+
+    virtual arrayElementCount nativeElementCount (
+            epicsGuard < epicsMutex > & ) const
+    {return 1;}
+};
+
+#endif // DBCHANNELNOOP_H
diff --git a/src/ioc/db/dbContext.cpp b/src/ioc/db/dbContext.cpp
index d005f084a..124a836cf 100644
--- a/src/ioc/db/dbContext.cpp
+++ b/src/ioc/db/dbContext.cpp
@@ -39,6 +39,7 @@
 #include "dbCAC.h"
 #include "dbChannel.h"
 #include "dbChannelIO.h"
+#include "dbChannelNOOP.h"
 #include "dbPutNotifyBlocker.h"
 
 class dbService : public cacService {
@@ -61,9 +62,16 @@ cacContext & dbService::contextCreate (
         mutualExclusion, notify );
 }
 
+extern "C" int dbServiceIsolate;
+int dbServiceIsolate = 0;
+
 extern "C" void dbServiceIOInit ()
 {
-    caInstallDefaultService ( dbs );
+    static int init=0;
+    if(!init) {
+        caInstallDefaultService ( dbs );
+        init=1;
+    }
 }
 
 dbBaseIO::dbBaseIO () {}
@@ -72,7 +80,8 @@ dbContext::dbContext ( epicsMutex & cbMutexIn,
         epicsMutex & mutexIn, cacContextNotify & notifyIn ) :
     readNotifyCache ( mutexIn ), ctx ( 0 ),
     stateNotifyCacheSize ( 0 ), mutex ( mutexIn ), cbMutex ( cbMutexIn ),
-    notify ( notifyIn ), pNetContext ( 0 ), pStateNotifyCache ( 0 )
+    notify ( notifyIn ), pNetContext ( 0 ), pStateNotifyCache ( 0 ),
+    isolated(dbServiceIsolate)
 {
 }
 
@@ -92,7 +101,10 @@ cacChannel & dbContext::createChannel (
 
     dbChannel *dbch = dbChannel_create ( pName );
     if ( ! dbch ) {
-        if ( ! this->pNetContext.get() ) {
+        if ( isolated ) {
+            return *new dbChannelNOOP(pName, notifyIn);
+
+        } else if ( ! this->pNetContext.get() ) {
             this->pNetContext.reset (
                 & this->notify.createNetworkContext (
                     this->mutex, this->cbMutex ) );
diff --git a/src/ioc/misc/iocInit.c b/src/ioc/misc/iocInit.c
index a66de064a..508f0312d 100644
--- a/src/ioc/misc/iocInit.c
+++ b/src/ioc/misc/iocInit.c
@@ -693,6 +693,7 @@ int iocShutdown(void)
         dbProcessNotifyExit();
         iocshFree();
     }
+    dbCaShutdown();
     iocState = iocStopped;
     iocBuildMode = buildRSRV;
     return 0;