diff --git a/CHANGELOG.md b/CHANGELOG.md
index f58d8553c9..9e26c6bba6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -350,6 +350,7 @@ This resolves [#548](https://github.com/JarryShaw/PyPCAPKit/issues/548), which r
 - message text: the `epb_flags` and `pack_flags` length errors say `expected 4`, the length they check, rather than `expected 8` ([#2168](https://github.com/JarryShaw/PyPCAPKit/issues/2168), [#2179](https://github.com/JarryShaw/PyPCAPKit/pull/2179)), and the IPv4 TS option's unknown-flag warning and the Mobility Header's prefix error spell `timestamp` and `mobile` ([#2171](https://github.com/JarryShaw/PyPCAPKit/issues/2171), [#2189](https://github.com/JarryShaw/PyPCAPKit/pull/2189)).
 - IPX dissects its payload from a registry of its own, `IPX.__proto__`, keyed by IPX Packet Type, where it looked the Packet Type up as an IP protocol number, so a type 17 (NCP) payload parsed as `IPX:UDP` and type 4 as `IPX:IPv4`. No IPX-native protocol ships, so the payload is `Raw` unless one is registered ([#2169](https://github.com/JarryShaw/PyPCAPKit/issues/2169), [#2187](https://github.com/JarryShaw/PyPCAPKit/pull/2187)).
 - HIP's `ECHO_RESPONSE_UNSIGNED` maker builds an `EchoResponseUnsignedParameter` schema, where it built the request's; the octets were already right ([#2170](https://github.com/JarryShaw/PyPCAPKit/issues/2170), [#2188](https://github.com/JarryShaw/PyPCAPKit/pull/2188)).
+- The MPL option's `seed_type` and the SMF_DPD option's `tid_type` makers (of both HOPOPT and IPv6-Opts), and the HTTP/1.* start line's `status`, resolve a `str` enum name against their own enum when no `..._namespace` is given, where the `None` default made a name raise `ProtocolNotImplemented` ([#2356](https://github.com/JarryShaw/PyPCAPKit/issues/2356)).
 
 ### pcapkit.toolkit
 
diff --git a/docs/source/changelog/1.5.0.rst b/docs/source/changelog/1.5.0.rst
index f083f7c020..d78de75bc4 100644
--- a/docs/source/changelog/1.5.0.rst
+++ b/docs/source/changelog/1.5.0.rst
@@ -2755,6 +2755,11 @@ Fixed
 * HIP's ``ECHO_RESPONSE_UNSIGNED`` maker builds an ``EchoResponseUnsignedParameter``
   schema, where it built the request's; the octets were already right (:issue:`2170`,
   :pr:`2188`).
+* The MPL option's ``seed_type`` and the SMF_DPD option's ``tid_type`` makers (of
+  both HOPOPT and IPv6-Opts), and the HTTP/1.* start line's ``status``, resolve a
+  ``str`` enum name against their own enum when no ``..._namespace`` is given,
+  where the ``None`` default made a name raise :exc:`.ProtocolNotImplemented`
+  (:issue:`2356`).
 
 pcapkit.toolkit
 ---------------
diff --git a/pcapkit/protocols/application/httpv1.py b/pcapkit/protocols/application/httpv1.py
index fdb673b2ae..512be8f2dd 100644
--- a/pcapkit/protocols/application/httpv1.py
+++ b/pcapkit/protocols/application/httpv1.py
@@ -348,7 +348,10 @@ def _make_start_line(self, http_version: 'str | bytes', *,
 
             header_line = b'%s %s HTTP/%s\r\n' % (meth, uri_val, version)
         elif method is None and status is not None:
-            status_code = self._make_index(status, status_default, namespace=status_namespace,
+            # NOTE: ``status`` defaults to ``None``, so a :obj:`str` name has to be
+            # resolved against StatusCode when no namespace is given (#2356).
+            status_ns = status_namespace if status_namespace is not None else Enum_StatusCode
+            status_code = self._make_index(status, status_default, namespace=status_ns,
                                            reversed=status_reversed, pack=False)
             status_code_val = int(status_code)
 
diff --git a/pcapkit/protocols/internet/hopopt.py b/pcapkit/protocols/internet/hopopt.py
index 81376f5027..c72d3bfde3 100644
--- a/pcapkit/protocols/internet/hopopt.py
+++ b/pcapkit/protocols/internet/hopopt.py
@@ -1744,7 +1744,10 @@ def _make_opt_smf_dpd(self, code: 'Enum_Option', opt: 'Optional[Data_SMFIdentifi
             tid_len = len(tid_bytes)
 
             if tid_type is not None:
-                tid_kind = self._make_index(tid_type, tid_type_default, namespace=tid_type_namespace,
+                # NOTE: ``tid_type`` defaults to ``None``, so a :obj:`str` name has to be
+                # resolved against TaggerID when no namespace is given (#2356).
+                tid_type_ns = tid_type_namespace if tid_type_namespace is not None else Enum_TaggerID
+                tid_kind = self._make_index(tid_type, tid_type_default, namespace=tid_type_ns,
                                             reversed=tid_type_reversed, pack=False)
             elif tid_len == 0:
                 tid_kind = Enum_TaggerID.NULL
@@ -2054,7 +2057,10 @@ def _make_opt_mpl(self, code: 'Enum_Option', opt: 'Optional[Data_MPLOption]' = N
             seed = opt.seed_id
 
         if seed_type is not None:
-            kind = self._make_index(seed_type, seed_type_default, namespace=seed_type_namespace,
+            # NOTE: ``seed_type`` defaults to ``None``, so a :obj:`str` name has to be
+            # resolved against SeedID when no namespace is given (#2356).
+            seed_type_ns = seed_type_namespace if seed_type_namespace is not None else Enum_SeedID
+            kind = self._make_index(seed_type, seed_type_default, namespace=seed_type_ns,
                                     reversed=seed_type_reversed, pack=False)
         elif seed is None or isinstance(seed, ipaddress.IPv6Address):
             kind = Enum_SeedID.IPV6_SOURCE_ADDRESS
diff --git a/pcapkit/protocols/internet/ipv6_opts.py b/pcapkit/protocols/internet/ipv6_opts.py
index fe62f868d4..692f17d72f 100644
--- a/pcapkit/protocols/internet/ipv6_opts.py
+++ b/pcapkit/protocols/internet/ipv6_opts.py
@@ -1732,7 +1732,10 @@ def _make_opt_smf_dpd(self, code: 'Enum_Option', opt: 'Optional[Data_SMFIdentifi
             tid_len = len(tid_bytes)
 
             if tid_type is not None:
-                tid_kind = self._make_index(tid_type, tid_type_default, namespace=tid_type_namespace,
+                # NOTE: ``tid_type`` defaults to ``None``, so a :obj:`str` name has to be
+                # resolved against TaggerID when no namespace is given (#2356).
+                tid_type_ns = tid_type_namespace if tid_type_namespace is not None else Enum_TaggerID
+                tid_kind = self._make_index(tid_type, tid_type_default, namespace=tid_type_ns,
                                             reversed=tid_type_reversed, pack=False)
             elif tid_len == 0:
                 tid_kind = Enum_TaggerID.NULL
@@ -2042,7 +2045,10 @@ def _make_opt_mpl(self, code: 'Enum_Option', opt: 'Optional[Data_MPLOption]' = N
             seed = opt.seed_id
 
         if seed_type is not None:
-            kind = self._make_index(seed_type, seed_type_default, namespace=seed_type_namespace,
+            # NOTE: ``seed_type`` defaults to ``None``, so a :obj:`str` name has to be
+            # resolved against SeedID when no namespace is given (#2356).
+            seed_type_ns = seed_type_namespace if seed_type_namespace is not None else Enum_SeedID
+            kind = self._make_index(seed_type, seed_type_default, namespace=seed_type_ns,
                                     reversed=seed_type_reversed, pack=False)
         elif seed is None or isinstance(seed, ipaddress.IPv6Address):
             kind = Enum_SeedID.IPV6_SOURCE_ADDRESS
diff --git a/tests/protocols/test_make_str_enum_name_none_default_2356_unit.py b/tests/protocols/test_make_str_enum_name_none_default_2356_unit.py
new file mode 100644
index 0000000000..1d1723fe3c
--- /dev/null
+++ b/tests/protocols/test_make_str_enum_name_none_default_2356_unit.py
@@ -0,0 +1,91 @@
+# -*- coding: utf-8 -*-
+"""GitHub issue #2356: makers resolve a :obj:`str` enum name for a ``None`` default.
+
+:meth:`~pcapkit.protocols.protocol.Protocol._make_index` resolves a :obj:`str`
+name against the enum of the argument's default when no ``..._namespace`` is
+given, so the makers whose argument defaults to ``None`` -- the MPL option's
+``seed_type`` and the SMF_DPD option's ``tid_type`` (of both HOPOPT and
+IPv6-Opts), and the HTTP/1.* start line's ``status`` -- raised
+:exc:`~pcapkit.utilities.exceptions.ProtocolNotImplemented` for a name such as
+``'IPv4'``. They now fall back to the argument's own enum, and a name builds
+the same octets as the member it names.
+
+The classes are imported inside each test, after
+:func:`~tests._support.reimport_once_per_class`, so that they belong to the
+:mod:`pcapkit` import that is live when the test runs.
+
+"""
+
+import importlib
+import unittest
+
+from tests._support import reimport_once_per_class
+
+#: The protocol classes sharing the option makers, by module and class name.
+PROTOCOLS = (
+    ('pcapkit.protocols.internet.hopopt', 'HOPOPT'),
+    ('pcapkit.protocols.internet.ipv6_opts', 'IPv6_Opts'),
+)
+
+
+class TestMakeStrEnumNameNoneDefault(unittest.TestCase):
+    """Pin :obj:`str` enum names for the makers whose argument defaults to ``None``."""
+
+    def setUp(self) -> None:
+        reimport_once_per_class(self)
+
+    def _protocols(self) -> 'list[type]':
+        return [getattr(importlib.import_module(mod), name) for mod, name in PROTOCOLS]
+
+    def test_mpl_seed_type_by_name(self) -> None:
+        from pcapkit.const.ipv6.option import Option
+        from pcapkit.const.ipv6.seed_id import SeedID
+
+        for cls in self._protocols():
+            proto = object.__new__(cls)
+            for member in (SeedID.SEEDID_16_BIT_UNSIGNED_INTEGER, SeedID.SEEDID_64_BIT_UNSIGNED_INTEGER):
+                with self.subTest(protocol=cls.__name__, seed_type=member.name):
+                    by_member = proto._make_opt_mpl(Option.MPL_Option, seed_type=member, seed=1)
+                    by_name = proto._make_opt_mpl(Option.MPL_Option, seed_type=member.name, seed=1)
+                    self.assertEqual(by_name.pack(), by_member.pack())
+                    self.assertEqual(by_name.flags['type'], int(member))
+
+    def test_smf_dpd_tid_type_by_name(self) -> None:
+        from pcapkit.const.ipv6.option import Option
+        from pcapkit.const.ipv6.tagger_id import TaggerID
+
+        for cls in self._protocols():
+            proto = object.__new__(cls)
+            for member, tid in ((TaggerID.IPv4, b'\x0a\x00\x00\x01'), (TaggerID.DEFAULT, b'\x01\x02')):
+                with self.subTest(protocol=cls.__name__, tid_type=member.name):
+                    by_member = proto._make_opt_smf_dpd(Option.SMF_DPD, mode='I_DPD', tid_type=member,
+                                                        tid=tid, id=b'\x01')
+                    by_name = proto._make_opt_smf_dpd(Option.SMF_DPD, mode='I_DPD', tid_type=member.name,
+                                                      tid=tid, id=b'\x01')
+                    self.assertEqual(by_name.pack(), by_member.pack())
+
+    def test_http_status_by_name(self) -> None:
+        from pcapkit.const.http.status_code import StatusCode
+        from pcapkit.protocols.application.httpv1 import HTTP
+
+        proto = object.__new__(HTTP)
+        for member in (StatusCode.CODE_200, StatusCode.CODE_404):
+            with self.subTest(status=member.name):
+                line = proto._make_start_line('1.1', status=member.name)
+                self.assertTrue(line.startswith(b'HTTP/1.1 %d ' % int(member)), line)
+
+    def test_an_explicit_namespace_still_wins(self) -> None:
+        from pcapkit.const.ipv6.option import Option
+        from pcapkit.const.ipv6.seed_id import SeedID
+
+        for cls in self._protocols():
+            proto = object.__new__(cls)
+            with self.subTest(protocol=cls.__name__):
+                code = int(SeedID.SEEDID_16_BIT_UNSIGNED_INTEGER)
+                made = proto._make_opt_mpl(Option.MPL_Option, seed_type='short', seed=1,
+                                           seed_type_namespace={code: 'short'})
+                self.assertEqual(made.flags['type'], code)
+
+
+if __name__ == '__main__':
+    unittest.main()