diff --git a/docs/user-guide/Fuzzing.md b/docs/user-guide/Fuzzing.md
index 88a7d1f..8d0ee13 100644
--- a/docs/user-guide/Fuzzing.md
+++ b/docs/user-guide/Fuzzing.md
@@ -15,9 +15,9 @@ Inputs: (same as for test)
 
 ## How to invoke RESTler in fuzz-lean or fuzz mode
 
-```C:\RESTler\restler\restler.exe fuzz-lean --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --target_ip <IP address> --target_port <port number> --token_refresh_interval <time in seconds> --token_refresh_command <command>```
+```C:\RESTler\restler\restler.exe fuzz-lean --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --token_refresh_interval <time in seconds> --token_refresh_command <command>```
 
-```C:\RESTler\restler\restler.exe fuzz --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --target_ip <IP address> --target_port <port number> --token_refresh_interval <time in seconds> --token_refresh_command <command> --time_budget <max number of hours (default 1)```
+```C:\RESTler\restler\restler.exe fuzz --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --token_refresh_interval <time in seconds> --token_refresh_command <command> --time_budget <max number of hours (default 1)```
 
 An optional settings file can also be passed to RESTler by adding the command-line option `--settings <path_to_settings_file.json>`.
 For a list of available settings, see [SettingsFile](SettingsFile.md).
@@ -29,17 +29,17 @@ RESTLer will generate a sub-directory `Fuzz[Lean]\RestlerResults\experiment<GUID
 - `bug_buckets.txt` reports bugs found by RESTler. Those bugs are either "500 Internal Server Errors" found by the RESTler "main_driver" or property checker violations
 
     RESTler currently detects these different types of bugs:
-    
+
     - "500 Internal Server Errors" and any other 5xx errors are detected by the "main_driver"
-    
+
     - UseAfterFreeChecker detects that a deleted resource can still being accessed after deletion
-    
+
     - NameSpaceRuleChecker detects that an unauthorized user can access service resources
-    
+
     - ResourceHierarchyChecker detects that a child resource can be accessed from a non-parent resource
-    
+
     - LeakageRuleChecker detects that a failed resource creation leaks data in subsequent requests
-    
+
     - InvalidDynamicObjectChecker detects 500 errors or unexpected success status codes when invalid dynamic objects are sent in requests
 
     - PayloadBodyChecker detects 500 errors when fuzzing the JSON bodies of requests
diff --git a/docs/user-guide/Replay.md b/docs/user-guide/Replay.md
index b29d525..2d6bd32 100644
--- a/docs/user-guide/Replay.md
+++ b/docs/user-guide/Replay.md
@@ -1,16 +1,16 @@
 # How to reproduce bugs found by RESTler
 
-In *Replay* mode, RESTler can replay a sequence from a bug_bucket log that was created during a test or fuzzing run.  These bug_bucket logs can be found in the RestlerResults/experiment##/bug_buckets/ directory.  
+In *Replay* mode, RESTler can replay a sequence from a bug_bucket log that was created during a test or fuzzing run.  These bug_bucket logs can be found in the RestlerResults/experiment##/bug_buckets/ directory.
 
-## Using the replay log 
+## Using the replay log
 
 To reproduce a bug bucket using RESTler,
 send the following command (as an example):
 
-`C:\RESTler\restler\restler.exe replay --replay_log C:\restler-test\Test\RestlerResults\experiment20652\bug_buckets\PayloadBodyChecker_500_1.txt --target_ip 127.0.0.1 --target_port 8888 --token_refresh_command "<command>" --token_refresh_interval 30`
+`C:\RESTler\restler\restler.exe replay --replay_log C:\restler-test\Test\RestlerResults\experiment20652\bug_buckets\PayloadBodyChecker_500_1.txt --token_refresh_command "<command>" --token_refresh_interval 30`
 
-In this example, RESTler will replay the log `PayloadBodyChecker_500_1.txt`
-and send the requests to `127.0.0.1:8888`.
+In this example, RESTler will replay the log `PayloadBodyChecker_500_1.txt`.
+If authentication is required to replay the sequence, the authentication options must be specified during replay.
 
 As you can see above,
 the IP, port, and authorization token refresh command/interval are all used
@@ -30,7 +30,7 @@ Any resources created should be removed manually.
 
 ## Replay log format
 
-The replay log is created anytime a new bug bucket is reported. 
+The replay log is created anytime a new bug bucket is reported.
 This replay log consists of the full sequence of requests that were sent to create the bug.
 Each request is also paired with the corresponding response that was received from the server.
 Each request and response is displayed exactly as sent and received, including dynamic objects,
@@ -84,4 +84,4 @@ while max_async_wait_time will attempt to perform an asynchronous polling-wait b
 with a maximum resource-creation-wait-time of the max_async_wait_time setting.
 
 
-## 
\ No newline at end of file
+##
\ No newline at end of file
diff --git a/docs/user-guide/Testing.md b/docs/user-guide/Testing.md
index 2337afc..61f6309 100644
--- a/docs/user-guide/Testing.md
+++ b/docs/user-guide/Testing.md
@@ -17,7 +17,7 @@ Authentication options: configuring authentication is described in [Authenticati
 
 How to invoke RESTler in test mode:
 
-`C:\RESTler\restler\Restler.exe test --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --target_ip <IP address> --target_port <port number> --token_refresh_interval <time in seconds> --token_refresh_command <command>`
+`C:\RESTler\restler\Restler.exe test --grammar_file <RESTLer grammar.py file> --dictionary_file <RESTler fuzzing-dictionary.json file> --token_refresh_interval <time in seconds> --token_refresh_command <command>`
 
 Outputs: see the sub-directory Test
 
diff --git a/docs/user-guide/TutorialDemoServer.md b/docs/user-guide/TutorialDemoServer.md
index 83d8816..ed338b0 100644
--- a/docs/user-guide/TutorialDemoServer.md
+++ b/docs/user-guide/TutorialDemoServer.md
@@ -26,7 +26,7 @@ For this simple tutorial, we will use the default values automatically generated
 
 Let's run RESTler in test mode to see what specification coverage we get with this default RESTler grammar:
 
-`C:\RESTler\restler\restler.exe test --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --target_ip 127.0.0.1 --target_port 8888 --no_ssl`
+`C:\RESTler\restler\restler.exe test --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --no_ssl`
 
 (For help, run `C:\RESTler\restler\restler.exe --help`)
 
@@ -68,7 +68,7 @@ By looking at `network.testing.<...>.txt`, we can see that RESTler attempts to e
 
 Let's now try to run restler in Fuzz-lean mode.
 
-`C:\RESTler\restler\restler.exe fuzz-lean --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --target_ip 127.0.0.1 --target_port 8888 --no_ssl`
+`C:\RESTler\restler\restler.exe fuzz-lean --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --no_ssl`
 
 The results are in a new `FuzzLean` directory and the experiment results can be found in `C:\restler-test\FuzzLean\RestlerResults\experiment<...>\`. The `logs\` directory should contain the same coverage results as the previous Test run, but you should also now see a new `bug_buckets` directory.
 
@@ -97,7 +97,7 @@ Right above the body in the header you should also see `StructMissing_/id/checks
 
 Now let's try to fuzz:
 
-`C:\RESTler\restler\restler.exe fuzz --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --target_ip 127.0.0.1 --target_port 8888 --no_ssl --time_budget 1`
+`C:\RESTler\restler\restler.exe fuzz --grammar_file C:\restler-test\Compile\grammar.py --dictionary_file C:\restler-test\Compile\dict.json --settings C:\restler-test\Compile\engine_settings.json --no_ssl --time_budget 1`
 
 The new __time_budget__ parameter is the length, in hours, to perform the fuzzing run.
 
diff --git a/restler-quick-start.py b/restler-quick-start.py
index 2f27c09..bd83e8a 100644
--- a/restler-quick-start.py
+++ b/restler-quick-start.py
@@ -62,10 +62,14 @@ def test_spec(ip, port, use_ssl, compile_dir, restler_dll_path):
     """
     command = (
         f"dotnet {restler_dll_path} test --grammar_file {compile_dir.joinpath('grammar.py')} --dictionary_file {compile_dir.joinpath('dict.json')}"
-        f" --settings {compile_dir.joinpath('engine_settings.json')} --target_ip {ip} --target_port {port}"
+        f" --settings {compile_dir.joinpath('engine_settings.json')}"
     )
     if not use_ssl:
         command = f"{command} --no_ssl"
+    if ip is not None:
+        command = f"{command} --target_ip {ip}"
+    if port is not None:
+        command = f"{command} --target_port {port}"
 
     with usedir(RESTLER_TEMP_DIR):
         subprocess.run(command, shell=True)
@@ -78,10 +82,10 @@ if __name__ == '__main__':
                         type=str, required=True)
     parser.add_argument('--ip',
                         help='The IP of the service to test',
-                        type=str, required=True)
+                        type=str, required=False, default=None)
     parser.add_argument('--port',
                         help='The port of the service to test',
-                        type=str, required=True)
+                        type=str, required=False, default=None)
     parser.add_argument('--restler_drop_dir',
                         help="The path to the RESTler drop",
                         type=str, required=True)
diff --git a/restler/end_to_end_tests/test_quick_start.py b/restler/end_to_end_tests/test_quick_start.py
index 22766e3..7832211 100644
--- a/restler/end_to_end_tests/test_quick_start.py
+++ b/restler/end_to_end_tests/test_quick_start.py
@@ -36,7 +36,7 @@ if __name__ == '__main__':
     try:
         # Run the quick start script
         output = subprocess.run(
-            f'python ./restler-quick-start.py --api_spec_path {swagger_path} --ip 127.0.0.1 --port 8888 --restler_drop_dir {restler_drop_dir}',
+            f'python ./restler-quick-start.py --api_spec_path {swagger_path} --restler_drop_dir {restler_drop_dir}',
             shell=True, capture_output=True
         )
         # Kill demo server
diff --git a/restler/engine/core/driver.py b/restler/engine/core/driver.py
index 3e82435..90cdfbe 100644
--- a/restler/engine/core/driver.py
+++ b/restler/engine/core/driver.py
@@ -25,6 +25,7 @@ import engine.core.fuzzing_monitor as fuzzing_monitor
 from engine.core.requests import GrammarRequestCollection
 from engine.core.requests import FailureInformation
 from engine.core.request_utilities import execute_token_refresh_cmd
+from engine.core.request_utilities import get_hostname_from_line
 from engine.core.fuzzing_monitor import Monitor
 from engine.errors import TimeOutException
 from engine.errors import ExhaustSeqCollectionException
@@ -720,6 +721,13 @@ def replay_sequence_from_log(replay_log_filename, token_refresh_cmd):
                 line = line.rstrip('\n')
                 line = line.replace('\\r', '\r')
                 line = line.replace('\\n', '\n')
+                if not Settings().host:
+                    # Extract hostname from request
+                    hostname = get_hostname_from_line(line)
+                    if hostname is None:
+                        raise Exception("Host not found in request. The replay log may be corrupted.")
+                    Settings().set_hostname(hostname)
+
                 # Append the request data to the list
                 # None is for the parser, which does not currently run during replays.
                 send_data.append(sequences.SentRequestData(line, None))
diff --git a/restler/engine/core/request_utilities.py b/restler/engine/core/request_utilities.py
index 798c983..7b7baca 100644
--- a/restler/engine/core/request_utilities.py
+++ b/restler/engine/core/request_utilities.py
@@ -24,6 +24,8 @@ last_refresh = 0
 latest_token_value = 'NO-TOKEN-SPECIFIED'
 latest_shadow_token_value = 'NO-SHADOW-TOKEN-SPECIFIED'
 
+HOST_PREFIX = 'Host: '
+
 class EmptyTokenException(Exception):
     pass
 
@@ -251,6 +253,20 @@ def call_response_parser(parser, response, request=None):
         return False
     return True
 
+def get_hostname_from_line(line):
+    """ Gets the hostname from a request definition's Host: line
+
+    @param line: The line to extract the hostname
+    @type  line: Str
+    @return: The hostname or None if not found
+    @rtype : Str or None
+
+    """
+    try:
+        return line.split(HOST_PREFIX, 1)[1].split('\r\n', 1)[0]
+    except:
+        return None
+
 def _RAW_LOGGING(log_str):
     """ Wrapper for the raw network logging function.
     Necessary to avoid circular dependency with logging.
diff --git a/restler/engine/core/requests.py b/restler/engine/core/requests.py
index 945a938..3720ab7 100644
--- a/restler/engine/core/requests.py
+++ b/restler/engine/core/requests.py
@@ -26,6 +26,9 @@ from enum import Enum
 class EmptyRequestException(Exception):
     pass
 
+class InvalidGrammarException(Exception):
+    pass
+
 class FailureInformation(Enum):
     SEQUENCE = 1
     RESOURCE_CREATION = 2
@@ -374,18 +377,51 @@ class Request(object):
                     self._consumes.remove(var_name)
         self._create_once_requests += rendered_sequence.sequence.sent_request_data_list
 
+    def get_host_index(self):
+        """ Gets the index of the definition line containing the Host parameter
+
+        @return: The index of the Host parameter or -1 if not found
+        @rtype : Int
+
+        """
+        for i, line in enumerate(self._definition):
+            try:
+                if isinstance(line[1], str) and line[1].startswith(request_utilities.HOST_PREFIX):
+                    return i
+            except:
+                # ignore line parsing exceptions - error will be returned if host not found
+                pass
+        return -1
+
     def update_host(self):
         """ Updates the Host field for every request with the one specified in Settings
 
         @return: None
         @rtype : None
 
+        """
+        new_host_line = primitives.restler_static_string(f"{request_utilities.HOST_PREFIX}{Settings().host}\r\n")
+        host_idx = self.get_host_index()
+        if host_idx >= 0:
+            self._definition[host_idx] = new_host_line
+        else:
+            # Host not in grammar, add it
+            header_idx = self.header_start_index()
+            if header_idx < 0:
+                raise InvalidGrammarException
+            self._definition.insert(header_idx, new_host_line)
+
+    def header_start_index(self):
+        """ Gets the index of the first header line in the definition
+
+        @return: The index of the first header line in the definition or -1 if not found
+        @rtype : Int
+
         """
         for i, line in enumerate(self._definition):
-            if isinstance(line[1], str) and line[1].startswith("Host: "):
-                self._definition[i] =\
-                    primitives.restler_static_string(f"Host: {Settings().host}\r\n")
-                break
+            if isinstance(line[1], str) and 'HTTP/1.1' in line[1]:
+                return i + 1
+        return -1
 
     def render_iter(self, candidate_values_pool, skip=0, preprocessing=False):
         """ This is the core method that renders values combinations in a
@@ -681,6 +717,19 @@ class RequestCollection(object):
         for req in self._requests:
             req.update_host()
 
+    def get_host_from_grammar(self):
+        """ Gets the hostname from the grammar
+
+        @return: The hostname or None if not found
+        @rtype : Str or None
+
+        """
+        for req in self._requests:
+            idx = req.get_host_index()
+            if idx >= 0:
+                return request_utilities.get_hostname_from_line(req._definition[idx][1])
+        return None
+
     def add_request(self, request):
         """ Adds a new request in the collection of requests.
 
diff --git a/restler/engine/transport_layer/messaging.py b/restler/engine/transport_layer/messaging.py
index 2a42a33..66aa793 100644
--- a/restler/engine/transport_layer/messaging.py
+++ b/restler/engine/transport_layer/messaging.py
@@ -37,23 +37,22 @@ class HttpSock(object):
         self._request_throttle_sec = (float)(Settings().request_throttle_ms/1000.0)\
             if Settings().request_throttle_ms else None
 
-        if connection_settings:
-            self.connection_settings = connection_settings
-        else:
-            self.connection_settings = ConnectionSettings('127.0.0.1', 80, use_ssl=True)
+        self.connection_settings = connection_settings
+
         try:
             self._sock = None
+            host = Settings().host
+            target_ip = self.connection_settings.target_ip or host
+            target_port = self.connection_settings.target_port
             if Settings().use_test_socket:
                 self._sock = TestSocket(Settings().test_server)
             elif self.connection_settings.use_ssl:
-                self._sock = ssl.wrap_socket(
-                    socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-                )
+                context = ssl.create_default_context()
+                with socket.create_connection((target_ip, target_port or 443)) as sock:
+                    self._sock = context.wrap_socket(sock, server_hostname=host)
             else:
                 self._sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-
-            server_address = (self.connection_settings.target_ip, self.connection_settings.target_port)
-            self._sock.connect(server_address)
+                self._sock.connect((target_ip, target_port or 80))
         except Exception as error:
             raise TransportLayerException(f"Exception Creating Socket: {error!s}")
 
diff --git a/restler/restler.py b/restler/restler.py
index 5cf0c19..3ca1f2a 100644
--- a/restler/restler.py
+++ b/restler/restler.py
@@ -403,7 +403,27 @@ if __name__ == '__main__':
     monitor.renderings_monitor.set_memoize_invalid_past_renderings_on()
 
     if settings.host:
-        req_collection.update_hosts()
+        try:
+            req_collection.update_hosts()
+        except requests.InvalidGrammarException:
+            sys.exit(-1)
+    else:
+        host = req_collection.get_host_from_grammar()
+        if host is not None:
+            if ':' in host:
+                # If hostname includes port, split it out
+                host_split = host.split(':')
+                host = host_split[0]
+                if settings.connection_settings.target_port is None:
+                    settings.set_port(host_split[1])
+            settings.set_hostname(host)
+        else:
+            logger.write_to_main(
+                "Host not found in grammar. "
+                "Add the host to your spec or launch RESTler with --host parameter.",
+                 print_to_console=True
+            )
+            sys.exit(-1)
 
     # Filter and get the requests to be used for fuzzing
     fuzzing_requests = preprocessing.create_fuzzing_req_collection(args.path_regex)
diff --git a/restler/restler_settings.py b/restler/restler_settings.py
index 1471fff..49a57bc 100644
--- a/restler/restler_settings.py
+++ b/restler/restler_settings.py
@@ -589,6 +589,29 @@ class RestlerSettings(object):
         self._custom_dictionaries.set_val(custom_dicts)
         self._create_once_endpoints.set_val(create_once_endpoints)
 
+    def set_hostname(self, hostname):
+        """ Sets the hostname
+
+        @param hostname: The hostname to set
+        @type  hostname: Str
+        @return: None
+        @rtype : None
+
+        """
+        self._host.val = hostname
+
+    def set_port(self, port):
+        """ Sets the port
+
+        @param port: The port to set
+        @type  port: Int
+        @return: None
+        @rtype : None
+
+        """
+        self._target_port.val = int(port)
+        self._connection_settings.target_port = int(port)
+
     def in_smoke_test_mode(self) -> bool:
         """ Returns whether or not we are running a smoke test
 
@@ -671,9 +694,5 @@ class RestlerSettings(object):
             raise OptionValidationError("Must specify command to refresh token")
         if self.token_refresh_cmd and not self.token_refresh_interval:
             raise OptionValidationError("Must specify refresh period in seconds")
-        if not self._target_ip.val:
-            raise OptionValidationError("Target IP is required")
-        if not self._target_port.val:
-            raise OptionValidationError("Target Port is required")
         if self.request_throttle_ms and self.fuzzing_jobs != 1:
             raise OptionValidationError("Request throttling not available for multiple fuzzing jobs")
diff --git a/restler/test_servers/README.md b/restler/test_servers/README.md
index 1bb74a4..8822366 100644
--- a/restler/test_servers/README.md
+++ b/restler/test_servers/README.md
@@ -1,7 +1,7 @@
 ## To run example in test mode:
 
 ```
-python -B C:\...restler\restler.py --fuzzing_mode directed-smoke-test --restler_grammar c:\...restler\test_servers\unit_test_server\test_grammar.py --custom_mutations c:\...restler\test_servers\unit_test_server\test_dict.json --target_ip 1.2.3.4 --target_port 443 --use_test_socket --garbage_collector_interval 30
+python -B C:\...restler\restler.py --fuzzing_mode directed-smoke-test --restler_grammar c:\...restler\test_servers\unit_test_server\test_grammar.py --custom_mutations c:\...restler\test_servers\unit_test_server\test_dict.json --use_test_socket --garbage_collector_interval 30
 ```
 
 test_grammar.py can be updated as any typical RESTler grammar.
@@ -18,7 +18,7 @@ test_grammar.py should pass the smoke test with 33/33 requests rendered,
 but the server is intentionally not free of errors.
 To return a test with planted bugs, run the same command with test_grammar_bugs.py:
 ```
-python -B C:\...restler\restler.py --fuzzing_mode directed-smoke-test --restler_grammar c:\...restler\test_servers\unit_test_server\test_grammar_bugs.py --custom_mutations c:\...restler\test_servers\unit_test_server\test_dict.json --target_ip 1.2.3.4 --target_port 443 --use_test_socket --garbage_collector_interval 30 --enable_checkers leakagerule useafterfree resourcehierarchy
+python -B C:\...restler\restler.py --fuzzing_mode directed-smoke-test --restler_grammar c:\...restler\test_servers\unit_test_server\test_grammar_bugs.py --custom_mutations c:\...restler\test_servers\unit_test_server\test_dict.json --use_test_socket --garbage_collector_interval 30 --enable_checkers leakagerule useafterfree resourcehierarchy
 ```
 
 
diff --git a/restler/unit_tests/test_basic_functionality_end_to_end.py b/restler/unit_tests/test_basic_functionality_end_to_end.py
index 97d89b7..b45e959 100644
--- a/restler/unit_tests/test_basic_functionality_end_to_end.py
+++ b/restler/unit_tests/test_basic_functionality_end_to_end.py
@@ -28,9 +28,8 @@ Restler_Path = os.path.join(os.path.dirname(__file__), '..', 'restler.py')
 
 Common_Settings = [
     "python", "-B", Restler_Path, "--use_test_socket",
-    '--target_ip', '1', '--target_port', '1',
     '--custom_mutations', f'{os.path.join(Test_File_Directory, "test_dict.json")}',
-    "--garbage_collection_interval", "30"
+    "--garbage_collection_interval", "30", "--host", "unittest"
 ]
 
 class FunctionalityTests(unittest.TestCase):
diff --git a/restler/unit_tests/test_restler_settings.py b/restler/unit_tests/test_restler_settings.py
index 3da44d0..d177446 100644
--- a/restler/unit_tests/test_restler_settings.py
+++ b/restler/unit_tests/test_restler_settings.py
@@ -339,18 +339,6 @@ class RestlerSettingsTest(unittest.TestCase):
         with self.assertRaises(InvalidValueError):
             RestlerSettings(user_args)
 
-    def test_missing_ip(self):
-        user_args = {'target_port': 500}
-        settings = RestlerSettings(user_args)
-        with self.assertRaises(OptionValidationError):
-            settings.validate_options()
-
-    def test_missing_port(self):
-        user_args = {'target_ip': '192.168.0.1'}
-        settings = RestlerSettings(user_args)
-        with self.assertRaises(OptionValidationError):
-            settings.validate_options()
-
     def test_random_walk_sequence_length(self):
         user_args = {'target_port': 500,
                      'target_ip': '192.168.0.1',
diff --git a/restler/utils/logger.py b/restler/utils/logger.py
index dce882e..3ea6349 100644
--- a/restler/utils/logger.py
+++ b/restler/utils/logger.py
@@ -383,7 +383,7 @@ def update_bug_buckets(bug_buckets, bug_request_data, bug_hash, additional_log_s
             print(f" Hash: {bug_hash}\n", file=bug_file)
             print(" To attempt to reproduce this bug using restler, run restler with the command", file=bug_file)
             print(" line option of --replay_log <path_to_this_log>.", file=bug_file)
-            print(" The other required options are target_ip, target_port, and token_refresh_cmd.", file=bug_file)
+            print(" If an authentication token is required, you must also specify the token_refresh_cmd.", file=bug_file)
             print("\n This log may contain specific values for IDs or names that were generated", file=bug_file)
             print(" during fuzzing, using the fuzzing dictionary. Such names will be re-played", file=bug_file)
             print(" without modification. You must update the replay log manually with any changes", file=bug_file)
diff --git a/src/driver/Program.fs b/src/driver/Program.fs
index 3de565f..f930be9 100644
--- a/src/driver/Program.fs
+++ b/src/driver/Program.fs
@@ -45,7 +45,9 @@ let usage() =
         --grammar_file <grammar file>
         --dictionary_file <dictionary file>
         --target_ip <ip>
+            If specified, sets the IP address to this specific value instead of using the hostname.
         --target_port <port>
+            If specified, overrides the default port, which is 443 with SSL, 80 with no SSL.
         --token_refresh_interval <interval with which to refresh the token>
         --token_refresh_command <full command line to refresh token.>
             The command line must be enclosed in double quotes. Paths must be absolute.
@@ -57,7 +59,7 @@ let usage() =
         --no_ssl
             When connecting to the service, do not use SSL.  The default is to connect with SSL.
         --host <Host string>
-            If specified, this string will override the Host in each request.
+            If specified, this string will set or override the Host in each request.
         --settings <engine settings file>
         --enable_checkers <list of checkers>
         --disable_checkers <list of checkers>
@@ -79,8 +81,6 @@ let usage() =
 
     replay options:
         <Required options from 'test' mode as above:
-            --target_ip
-            --target_port
             --token_refresh_cmd. >
         --replay_log <path to the RESTler bug bucket repro file>. "
     exit 1
@@ -168,8 +168,6 @@ module Fuzz =
         [
             sprintf "--restler_grammar \"%s\"" parameters.grammarFilePath
             sprintf "--custom_mutations \"%s\"" parameters.mutationsFilePath
-            sprintf "--target_ip %s" parameters.targetIp
-            sprintf "--target_port %s" parameters.targetPort
             sprintf "--set_version %s" CurrentVersion
 
             (match parameters.refreshableTokenOptions with
@@ -207,7 +205,12 @@ module Fuzz =
              | None -> ""
              | Some t ->
                 sprintf "--time_budget %f" t)
-
+            (match parameters.targetIp with
+             | Some t -> sprintf "--target_ip %s" t
+             | None -> "")
+            (match parameters.targetPort with
+             | Some t -> sprintf "--target_port %s" t
+             | None -> "")
             // internal options
             "--include_user_agent"
             "--no_tokens_in_logs t"
@@ -325,12 +328,6 @@ module Fuzz =
 let rec parseEngineArgs task (args:EngineParameters) = function
     | [] ->
         // Check for unspecified parameters
-        if args.targetIp = DefaultEngineParameters.targetIp then
-            Logging.logError <| sprintf "Target IP must be specified."
-            usage()
-        if args.targetPort = DefaultEngineParameters.targetPort then
-           Logging.logError <| sprintf "Target port must be specified."
-           usage()
         match task with
         | Compile ->
             failwith "Invalid function usage."
@@ -359,9 +356,9 @@ let rec parseEngineArgs task (args:EngineParameters) = function
             usage()
         parseEngineArgs task  { args with mutationsFilePath = Path.GetFullPath(mutationsFilePath) } rest
     | "--target_ip"::targetIp::rest ->
-        parseEngineArgs task { args with targetIp = targetIp } rest
+        parseEngineArgs task { args with targetIp = Some targetIp } rest
     | "--target_port"::targetPort::rest ->
-        parseEngineArgs task { args with targetPort = targetPort } rest
+        parseEngineArgs task { args with targetPort = Some targetPort } rest
     | "--token_refresh_command"::refreshCommand::rest ->
         let parameters = UserSpecifiedCommand refreshCommand
         let options =
diff --git a/src/driver/Types.fs b/src/driver/Types.fs
index 20b31d6..6859fa9 100644
--- a/src/driver/Types.fs
+++ b/src/driver/Types.fs
@@ -29,10 +29,10 @@ type EngineParameters =
         mutationsFilePath : string
 
         /// The IP of the endpoint being fuzzed
-        targetIp : string
+        targetIp : string option
 
         /// The port of the endpoint being fuzzed
-        targetPort : string
+        targetPort : string option
 
         /// The maximum fuzzing time in hours
         maxDurationHours : float
@@ -71,8 +71,8 @@ let DefaultEngineParameters =
     {
         grammarFilePath = ""
         mutationsFilePath = ""
-        targetIp = ""
-        targetPort = ""
+        targetIp = None
+        targetPort = None
         refreshableTokenOptions = None
         maxDurationHours = float 0
         producerTimingDelay = 0