diff --git a/util/hostandport.h b/util/hostandport.h
index d6b8242c241..985e2529de7 100644
--- a/util/hostandport.h
+++ b/util/hostandport.h
@@ -28,7 +28,7 @@ namespace mongo {
     /** helper for manipulating host:port connection endpoints. 
       */
     struct HostAndPort { 
-        HostAndPort() : _port(-1) { }
+        HostAndPort() : _port(-1), _isSelf(NOT_CACHED) { }
 
         /** From a string hostname[:portnumber] 
             Throws user assertion if bad config string or bad port #.
@@ -36,10 +36,10 @@ namespace mongo {
         HostAndPort(string s);
 
         /** @param p port number. -1 is ok to use default. */
-        HostAndPort(string h, int p /*= -1*/) : _host(h), _port(p) { }
+        HostAndPort(string h, int p /*= -1*/) : _host(h), _port(p), _isSelf(NOT_CACHED) { }
 
         HostAndPort(const SockAddr& sock ) 
-            : _host( sock.getAddr() ) , _port( sock.getPort() ){
+            : _host( sock.getAddr() ) , _port( sock.getPort() ), _isSelf(NOT_CACHED){
         }
 
         static HostAndPort me() { 
@@ -62,7 +62,7 @@ namespace mongo {
         }
 
         /* returns true if the host/port combo identifies this process instance. */
-        bool isSelf() const;
+        bool isSelf() const; // defined in message.cpp
 
         bool isLocalHost() const;
 
@@ -80,6 +80,12 @@ namespace mongo {
         // invariant (except full obj assignment):
         string _host;
         int _port; // -1 indicates unspecified
+
+        mutable enum {
+            NOT_CACHED = -1,
+            NO = 0,
+            YES = 1
+        } _isSelf;
     };
 
     /** returns true if strings seem to be the same hostname.
@@ -98,14 +104,6 @@ namespace mongo {
         return HostAndPort(h, cmdLine.port);
     }
 
-    inline bool HostAndPort::isSelf() const { 
-        int p = _port == -1 ? CmdLine::DefaultDBPort : _port;
-        if( p != cmdLine.port )
-            return false;
-        
-        return sameHostname(getHostName(), _host) || isLocalHost();
-    }
-
     inline string HostAndPort::toString() const {
         stringstream ss;
         ss << _host;
@@ -127,7 +125,7 @@ namespace mongo {
         return _host == "localhost" || startsWith(_host.c_str(), "127.") || _host == "::1";
     }
 
-    inline HostAndPort::HostAndPort(string s) {
+    inline HostAndPort::HostAndPort(string s) : _isSelf(NOT_CACHED) {
         const char *p = s.c_str();
         uassert(13110, "HostAndPort: bad config string", *p);
         const char *colon = strrchr(p, ':');
diff --git a/util/message.cpp b/util/message.cpp
index 2c91d051f60..c7dc2aa455b 100644
--- a/util/message.cpp
+++ b/util/message.cpp
@@ -690,5 +690,28 @@ namespace mongo {
 
     TicketHolder connTicketHolder(20000);
     
+    bool HostAndPort::isSelf() const { 
+        if (_isSelf == NOT_CACHED){
+            int p = _port == -1 ? CmdLine::DefaultDBPort : _port;
+
+            if( p != cmdLine.port ){
+                _isSelf = NO;
+            } else if (sameHostname(getHostName(), _host) || isLocalHost()) {
+                _isSelf = YES;
+            } else {
+                SockAddr addr (_host.c_str(), 0); // port 0 is dynamically assigned
+                SOCKET sock = ::socket(addr.getType(), SOCK_STREAM, 0);
+                assert(sock != INVALID_SOCKET);
+
+                _isSelf = ( (::bind(sock, addr.raw(), addr.addressSize) == 0) ? YES : NO );
+
+                closesocket(sock);
+            }
+        }
+
+        assert(_isSelf != NOT_CACHED);
+
+        return _isSelf;
+    }
 
 } // namespace mongo