When Ping is called and MongoServer is connected to a replica set, Ping now pings all members of the replica set one at a time, instead of just the Primary. Also added a Ping method to MongoServerInstance, so individual instances can be pinged if desired.

Driver/Core/MongoServer.cs

@@ -811,11 +811,12 @@ namespace MongoDB.Driver {
         }
 
         /// <summary>
-        /// Checks whether the server is alive (throws an exception if not).
+        /// Checks whether the server is alive (throws an exception if not). If server is a replica set, pings all members one at a time.
         /// </summary>
         public virtual void Ping() {
-            var command = new CommandDocument("ping", 1);
-            RunAdminCommand(command);
+            foreach (var instance in instances.ToArray()) {
+                instance.Ping();
+            }
         }
 
         /// <summary>

Driver/Core/MongoServerInstance.cs

@@ -187,6 +187,21 @@ namespace MongoDB.Driver {
         }
         #endregion
 
+        #region public method
+        /// <summary>
+        /// Checks whether the server is alive (throws an exception if not).
+        /// </summary>
+        public void Ping() {
+            var connection = connectionPool.AcquireConnection(null);
+            try {
+                var pingCommand = new CommandDocument("ping", 1);
+                connection.RunCommand("admin.$cmd", QueryFlags.SlaveOk, pingCommand);
+            } finally {
+                connection.ConnectionPool.ReleaseConnection(connection);
+            }
+        }
+        #endregion
+
         #region internal methods
         internal MongoConnection AcquireConnection(
             MongoDatabase database