diff --git a/synapse/api/auth/__init__.py b/synapse/api/auth/__init__.py
index d253938329b..0dd520cdae7 100644
--- a/synapse/api/auth/__init__.py
+++ b/synapse/api/auth/__init__.py
@@ -188,6 +188,22 @@ def get_access_token_from_request(request: Request) -> str:
                 request
         """
 
+    @staticmethod
+    def get_ip_address_from_request(request: Request) -> str:
+        """
+        Extract the IPv4 or IPv6 address from a client request.
+
+        Args:
+            request: The request to process.
+
+        Returns:
+            The IPv4 or IPv6 address of the client.
+
+        Raises:
+            SynapseError: If an IP address could not be extracted from the
+                request.
+        """
+
     async def check_user_in_room_or_world_readable(
         self, room_id: str, requester: Requester, allow_departed_users: bool = False
     ) -> Tuple[str, Optional[str]]:
diff --git a/synapse/api/auth/base.py b/synapse/api/auth/base.py
index 76c8c71628a..e78ad7b21b6 100644
--- a/synapse/api/auth/base.py
+++ b/synapse/api/auth/base.py
@@ -19,10 +19,12 @@
 #
 #
 import logging
+from http import HTTPStatus
 from typing import TYPE_CHECKING, Optional, Tuple
 
 from netaddr import IPAddress
 
+from twisted.internet.address import IPv4Address, IPv6Address
 from twisted.web.server import Request
 
 from synapse import event_auth
@@ -31,6 +33,7 @@
     AuthError,
     Codes,
     MissingClientTokenError,
+    SynapseError,
     UnstableSpecAuthError,
 )
 from synapse.appservice import ApplicationService
@@ -291,6 +294,37 @@ def get_access_token_from_request(request: Request) -> str:
 
             return query_params[0].decode("ascii")
 
+    @staticmethod
+    def get_ip_address_from_request(request: Request) -> str:
+        """
+        Extract the IPv4 or IPv6 address from a client request.
+
+        Args:
+            request: The request to process.
+
+        Returns:
+            The IPv4 or IPv6 address of the client.
+
+        Raises:
+            SynapseError: If an IP address could not be extracted from the
+                request.
+        """
+        client_address = request.getClientAddress()
+        if not isinstance(client_address, IPv4Address) and not isinstance(
+            client_address, IPv6Address
+        ):
+            logger.error(
+                "Unable to view IP address of the requester. " \
+                "Check that you are setting the X-Forwarded-For header correctly in your reverse proxy."
+            )
+            raise SynapseError(
+                HTTPStatus.INTERNAL_SERVER_ERROR,
+                "Unable to read client IP address",
+                Codes.UNKNOWN,
+            )
+
+        return client_address.host
+
     @cancellable
     async def get_appservice_user(
         self, request: Request, access_token: str
@@ -326,7 +360,8 @@ async def get_appservice_user(
             return None
 
         if app_service.ip_range_whitelist:
-            ip_address = IPAddress(request.getClientAddress().host)
+            ip_address_str = self.get_ip_address_from_request(request)
+            ip_address = IPAddress(ip_address_str)
             if ip_address not in app_service.ip_range_whitelist:
                 return None
 
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 2d1990cce5b..fba86bb7c20 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -567,7 +567,7 @@ async def check_ui_auth(
             await self.store.set_ui_auth_clientdict(sid, clientdict)
 
         user_agent = get_request_user_agent(request)
-        clientip = request.getClientAddress().host
+        clientip = self.auth.get_ip_address_from_request(request)
 
         await self.store.add_user_agent_ip_to_ui_auth_session(
             session.session_id, user_agent, clientip
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index be757201fc6..fa49f47db2c 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -57,6 +57,7 @@
 
 class IdentityHandler:
     def __init__(self, hs: "HomeServer"):
+        self._auth = hs.get_auth()
         self.store = hs.get_datastores().main
         # An HTTP client for contacting trusted URLs.
         self.http_client = SimpleHttpClient(hs)
@@ -97,9 +98,8 @@ async def ratelimit_request_token_requests(
             address: The actual threepid ID, e.g. the phone number or email address
         """
 
-        await self._3pid_validation_ratelimiter_ip.ratelimit(
-            None, (medium, request.getClientAddress().host)
-        )
+        ip_address = self._auth.get_ip_address_from_request(request)
+        await self._3pid_validation_ratelimiter_ip.ratelimit(None, (medium, ip_address))
         await self._3pid_validation_ratelimiter_address.ratelimit(
             None, (medium, address)
         )
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 735cfa0a0f8..cc13a284ca7 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -205,6 +205,7 @@ def __init__(self, hs: "HomeServer"):
         self.server_name = hs.hostname
         self._is_mine_server_name = hs.is_mine_server_name
         self._registration_handler = hs.get_registration_handler()
+        self._auth = hs.get_auth()
         self._auth_handler = hs.get_auth_handler()
         self._device_handler = hs.get_device_handler()
         self._error_template = hs.config.sso.sso_error_template
@@ -505,12 +506,13 @@ async def complete_sso_login_request(
                         auth_provider_session_id,
                     )
 
+                ip_address = self._auth.get_ip_address_from_request(request)
                 user_id = await self._register_mapped_user(
                     attributes,
                     auth_provider_id,
                     remote_user_id,
                     get_request_user_agent(request),
-                    request.getClientAddress().host,
+                    ip_address,
                 )
                 new_user = True
             elif self._sso_update_profile_information:
@@ -1080,6 +1082,8 @@ async def register_sso_user(self, request: Request, session_id: str) -> None:
         if session.use_avatar:
             attributes.picture = session.avatar_url
 
+        ip_address = self._auth.get_ip_address_from_request(request)
+
         # the following will raise a 400 error if the username has been taken in the
         # meantime.
         user_id = await self._register_mapped_user(
@@ -1087,7 +1091,7 @@ async def register_sso_user(self, request: Request, session_id: str) -> None:
             session.auth_provider_id,
             session.remote_user_id,
             get_request_user_agent(request),
-            request.getClientAddress().host,
+            ip_address,
         )
 
         logger.info(
diff --git a/synapse/rest/client/auth.py b/synapse/rest/client/auth.py
index 600bb51a7e7..c74af357463 100644
--- a/synapse/rest/client/auth.py
+++ b/synapse/rest/client/auth.py
@@ -134,6 +134,8 @@ async def on_POST(self, request: Request, stagetype: str) -> None:
         if not session:
             raise SynapseError(400, "No session supplied")
 
+        ip_address = self.auth.get_ip_address_from_request(request)
+
         if stagetype == LoginType.RECAPTCHA:
             response = parse_string(request, "g-recaptcha-response")
 
@@ -144,7 +146,9 @@ async def on_POST(self, request: Request, stagetype: str) -> None:
 
             try:
                 await self.auth_handler.add_oob_auth(
-                    LoginType.RECAPTCHA, authdict, request.getClientAddress().host
+                    LoginType.RECAPTCHA,
+                    authdict,
+                    ip_address,
                 )
             except LoginError as e:
                 # Authentication failed, let user try again
@@ -164,7 +168,9 @@ async def on_POST(self, request: Request, stagetype: str) -> None:
 
             try:
                 await self.auth_handler.add_oob_auth(
-                    LoginType.TERMS, authdict, request.getClientAddress().host
+                    LoginType.TERMS,
+                    authdict,
+                    ip_address,
                 )
             except LoginError as e:
                 # Authentication failed, let user try again
@@ -195,7 +201,7 @@ async def on_POST(self, request: Request, stagetype: str) -> None:
                 await self.auth_handler.add_oob_auth(
                     LoginType.REGISTRATION_TOKEN,
                     authdict,
-                    request.getClientAddress().host,
+                    ip_address,
                 )
             except LoginError as e:
                 html = self.registration_token_template.render(
diff --git a/synapse/rest/client/login.py b/synapse/rest/client/login.py
index 921232a3ea4..5ee4ba1176f 100644
--- a/synapse/rest/client/login.py
+++ b/synapse/rest/client/login.py
@@ -205,6 +205,7 @@ async def on_POST(self, request: SynapseRequest) -> Tuple[int, LoginResponse]:
         )
 
         request_info = request.request_info()
+        ip_address = self.auth.get_ip_address_from_request(request)
 
         try:
             if login_submission["type"] == LoginRestServlet.APPSERVICE_TYPE:
@@ -224,9 +225,7 @@ async def on_POST(self, request: SynapseRequest) -> Tuple[int, LoginResponse]:
                     )
 
                 if appservice.is_rate_limited():
-                    await self._address_ratelimiter.ratelimit(
-                        None, request.getClientAddress().host
-                    )
+                    await self._address_ratelimiter.ratelimit(None, ip_address)
 
                 result = await self._do_appservice_login(
                     login_submission,
@@ -238,27 +237,21 @@ async def on_POST(self, request: SynapseRequest) -> Tuple[int, LoginResponse]:
                 self.jwt_enabled
                 and login_submission["type"] == LoginRestServlet.JWT_TYPE
             ):
-                await self._address_ratelimiter.ratelimit(
-                    None, request.getClientAddress().host
-                )
+                await self._address_ratelimiter.ratelimit(None, ip_address)
                 result = await self._do_jwt_login(
                     login_submission,
                     should_issue_refresh_token=should_issue_refresh_token,
                     request_info=request_info,
                 )
             elif login_submission["type"] == LoginRestServlet.TOKEN_TYPE:
-                await self._address_ratelimiter.ratelimit(
-                    None, request.getClientAddress().host
-                )
+                await self._address_ratelimiter.ratelimit(None, ip_address)
                 result = await self._do_token_login(
                     login_submission,
                     should_issue_refresh_token=should_issue_refresh_token,
                     request_info=request_info,
                 )
             else:
-                await self._address_ratelimiter.ratelimit(
-                    None, request.getClientAddress().host
-                )
+                await self._address_ratelimiter.ratelimit(None, ip_address)
                 result = await self._do_other_login(
                     login_submission,
                     should_issue_refresh_token=should_issue_refresh_token,
diff --git a/synapse/rest/client/media.py b/synapse/rest/client/media.py
index 4c044ae900e..43732bae06d 100644
--- a/synapse/rest/client/media.py
+++ b/synapse/rest/client/media.py
@@ -192,7 +192,8 @@ async def on_GET(
                 respond_404(request)
                 return
 
-            ip_address = request.getClientAddress().host
+            ip_address = self.auth.get_ip_address_from_request(request)
+
             remote_resp_function = (
                 self.thumbnailer.select_or_generate_remote_thumbnail
                 if self.dynamic_thumbnails
@@ -263,7 +264,8 @@ async def on_GET(
                 request, media_id, file_name, max_timeout_ms
             )
         else:
-            ip_address = request.getClientAddress().host
+            ip_address = self.auth.get_ip_address_from_request(request)
+
             await self.media_repo.get_remote_media(
                 request,
                 server_name,
diff --git a/synapse/rest/client/register.py b/synapse/rest/client/register.py
index b42006e4cee..3798f46ae13 100644
--- a/synapse/rest/client/register.py
+++ b/synapse/rest/client/register.py
@@ -329,6 +329,7 @@ class UsernameAvailabilityRestServlet(RestServlet):
     def __init__(self, hs: "HomeServer"):
         super().__init__()
         self.hs = hs
+        self._auth = hs.get_auth()
         self.server_name = hs.hostname
         self.registration_handler = hs.get_registration_handler()
         self.ratelimiter = FederationRateLimiter(
@@ -361,7 +362,7 @@ async def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
         if self.inhibit_user_in_use_error:
             return 200, {"available": True}
 
-        ip = request.getClientAddress().host
+        ip = self._auth.get_ip_address_from_request(request)
         with self.ratelimiter.ratelimit(ip) as wait_deferred:
             await wait_deferred
 
@@ -395,6 +396,7 @@ class RegistrationTokenValidityRestServlet(RestServlet):
     def __init__(self, hs: "HomeServer"):
         super().__init__()
         self.hs = hs
+        self._auth = hs.get_auth()
         self.store = hs.get_datastores().main
         self.ratelimiter = Ratelimiter(
             store=self.store,
@@ -403,7 +405,8 @@ def __init__(self, hs: "HomeServer"):
         )
 
     async def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
-        await self.ratelimiter.ratelimit(None, (request.getClientAddress().host,))
+        ip_address = self._auth.get_ip_address_from_request(request)
+        await self.ratelimiter.ratelimit(None, (ip_address,))
 
         if not self.hs.config.registration.enable_registration:
             raise SynapseError(
@@ -456,7 +459,7 @@ def __init__(self, hs: "HomeServer"):
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         body = parse_json_object_from_request(request)
 
-        client_addr = request.getClientAddress().host
+        client_addr = self.auth.get_ip_address_from_request(request)
 
         await self.ratelimiter.ratelimit(None, client_addr, update=False)
 
@@ -916,7 +919,7 @@ def __init__(self, hs: "HomeServer"):
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         body = parse_json_object_from_request(request)
 
-        client_addr = request.getClientAddress().host
+        client_addr = self.auth.get_ip_address_from_request(request)
 
         await self.ratelimiter.ratelimit(None, client_addr, update=False)
 
diff --git a/synapse/rest/media/download_resource.py b/synapse/rest/media/download_resource.py
index 3c3f703667a..2a29cfd1c9d 100644
--- a/synapse/rest/media/download_resource.py
+++ b/synapse/rest/media/download_resource.py
@@ -49,6 +49,7 @@ class DownloadResource(RestServlet):
 
     def __init__(self, hs: "HomeServer", media_repo: "MediaRepository"):
         super().__init__()
+        self._auth = hs.get_auth()
         self.media_repo = media_repo
         self._is_mine_server_name = hs.is_mine_server_name
 
@@ -97,7 +98,7 @@ async def on_GET(
                 respond_404(request)
                 return
 
-            ip_address = request.getClientAddress().host
+            ip_address = self._auth.get_ip_address_from_request(request)
             await self.media_repo.get_remote_media(
                 request,
                 server_name,
diff --git a/synapse/rest/media/thumbnail_resource.py b/synapse/rest/media/thumbnail_resource.py
index 536fea4c32f..5701f0d99e0 100644
--- a/synapse/rest/media/thumbnail_resource.py
+++ b/synapse/rest/media/thumbnail_resource.py
@@ -58,6 +58,7 @@ def __init__(
     ):
         super().__init__()
 
+        self._auth = hs.get_auth()
         self.store = hs.get_datastores().main
         self.media_repo = media_repo
         self.media_storage = media_storage
@@ -120,7 +121,7 @@ async def on_GET(
                 respond_404(request)
                 return
 
-            ip_address = request.getClientAddress().host
+            ip_address = self._auth.get_ip_address_from_request(request)
             remote_resp_function = (
                 self.thumbnail_provider.select_or_generate_remote_thumbnail
                 if self.dynamic_thumbnails
diff --git a/tests/api/test_auth.py b/tests/api/test_auth.py
index e7fcd928d71..1907a33112e 100644
--- a/tests/api/test_auth.py
+++ b/tests/api/test_auth.py
@@ -23,6 +23,7 @@
 
 import pymacaroons
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.api.auth.internal import InternalAuth
@@ -118,7 +119,7 @@ def test_get_user_by_req_appservice_valid_token(self) -> None:
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         requester = self.get_success(self.auth.get_user_by_req(request))
@@ -137,7 +138,7 @@ def test_get_user_by_req_appservice_valid_token_good_ip(self) -> None:
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "192.168.10.10"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="192.168.10.10", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         requester = self.get_success(self.auth.get_user_by_req(request))
@@ -156,7 +157,7 @@ def test_get_user_by_req_appservice_valid_token_bad_ip(self) -> None:
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "131.111.8.42"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="131.111.8.42", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         f = self.get_failure(
@@ -209,7 +210,7 @@ class FakeUserInfo:
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
@@ -231,7 +232,7 @@ def test_get_user_by_req_appservice_valid_token_bad_user_id(self) -> None:
         self.store.get_user_by_access_token = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
@@ -261,7 +262,7 @@ def test_get_user_by_req_appservice_valid_token_valid_device_id(self) -> None:
         self.store.get_device = AsyncMock(return_value={"hidden": False})
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.args[b"org.matrix.msc3202.device_id"] = [masquerading_device_id]
@@ -296,7 +297,7 @@ def test_get_user_by_req_appservice_valid_token_invalid_device_id(self) -> None:
         self.store.get_device = AsyncMock(return_value=None)
 
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.args[b"user_id"] = [masquerading_user_id]
         request.args[b"org.matrix.msc3202.device_id"] = [masquerading_device_id]
@@ -320,7 +321,7 @@ def test_get_user_by_req__puppeted_token__not_tracking_puppeted_mau(self) -> Non
         self.store.mark_access_token_as_used = AsyncMock(return_value=None)
         self.store.get_user_locked_status = AsyncMock(return_value=False)
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         self.get_success(self.auth.get_user_by_req(request))
@@ -341,7 +342,7 @@ def test_get_user_by_req__puppeted_token__tracking_puppeted_mau(self) -> None:
         self.store.insert_client_ip = AsyncMock(return_value=None)
         self.store.mark_access_token_as_used = AsyncMock(return_value=None)
         request = Mock(args={})
-        request.getClientAddress.return_value.host = "127.0.0.1"
+        request.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
         request.args[b"access_token"] = [self.test_token]
         request.requestHeaders.getRawHeaders = mock_getRawHeaders()
         self.get_success(self.auth.get_user_by_req(request))
diff --git a/tests/handlers/test_cas.py b/tests/handlers/test_cas.py
index f677f3be2a6..1135b38f2fb 100644
--- a/tests/handlers/test_cas.py
+++ b/tests/handlers/test_cas.py
@@ -21,6 +21,7 @@
 from typing import Any, Dict
 from unittest.mock import AsyncMock, Mock
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.handlers.cas import CasResponse
@@ -234,6 +235,7 @@ def _mock_request() -> Mock:
             "write",
         ]
     )
+    mock.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
     # `_disconnected` musn't be another `Mock`, otherwise it will be truthy.
     mock._disconnected = False
     return mock
diff --git a/tests/handlers/test_oidc.py b/tests/handlers/test_oidc.py
index 5207382f00f..37a006fa0f7 100644
--- a/tests/handlers/test_oidc.py
+++ b/tests/handlers/test_oidc.py
@@ -25,6 +25,7 @@
 
 import pymacaroons
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.handlers.sso import MappingException
@@ -1684,5 +1685,5 @@ def _build_callback_request(
     request.args = {}
     request.args[b"code"] = [code.encode("utf-8")]
     request.args[b"state"] = [state.encode("utf-8")]
-    request.getClientAddress.return_value.host = ip_address
+    request.getClientAddress.return_value = IPv4Address(type="TCP", host=ip_address, port=12345)
     return request
diff --git a/tests/handlers/test_saml.py b/tests/handlers/test_saml.py
index f7cbf911139..77c07564d96 100644
--- a/tests/handlers/test_saml.py
+++ b/tests/handlers/test_saml.py
@@ -24,6 +24,7 @@
 
 import attr
 
+from twisted.internet.address import IPv4Address
 from twisted.internet.testing import MemoryReactor
 
 from synapse.api.errors import RedirectException
@@ -424,4 +425,5 @@ def _mock_request() -> Mock:
     )
     # `_disconnected` musn't be another `Mock`, otherwise it will be truthy.
     mock._disconnected = False
+    mock.getClientAddress.return_value = IPv4Address(type="TCP", host="127.0.0.1", port=12345)
     return mock