diff --git a/changelog.d/3847.misc b/changelog.d/3847.misc
new file mode 100644
index 000000000..bf8b5afea
--- /dev/null
+++ b/changelog.d/3847.misc
@@ -0,0 +1 @@
+federation/ is now ported to Python 3.
\ No newline at end of file
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index c9f3c2d35..fe67b2ff4 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -271,10 +271,10 @@ class FederationClient(FederationBase):
                     event_id, destination, e,
                 )
             except NotRetryingDestination as e:
-                logger.info(e.message)
+                logger.info(str(e))
                 continue
             except FederationDeniedError as e:
-                logger.info(e.message)
+                logger.info(str(e))
                 continue
             except Exception as e:
                 pdu_attempts[destination] = now
@@ -510,7 +510,7 @@ class FederationClient(FederationBase):
                 else:
                     logger.warn(
                         "Failed to %s via %s: %i %s",
-                        description, destination, e.code, e.message,
+                        description, destination, e.code, e.args[0],
                     )
             except Exception:
                 logger.warn(
@@ -875,7 +875,7 @@ class FederationClient(FederationBase):
             except Exception as e:
                 logger.exception(
                     "Failed to send_third_party_invite via %s: %s",
-                    destination, e.message
+                    destination, str(e)
                 )
 
         raise RuntimeError("Failed to send to any server.")
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 1054441ca..2ab973d6c 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -15,7 +15,8 @@
 # limitations under the License.
 
 import logging
-import urllib
+
+from six.moves import urllib
 
 from twisted.internet import defer
 
@@ -951,4 +952,4 @@ def _create_path(prefix, path, *args):
     Returns:
         str
     """
-    return prefix + path % tuple(urllib.quote(arg, "") for arg in args)
+    return prefix + path % tuple(urllib.parse.quote(arg, "") for arg in args)
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 3972922ff..2f874b483 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -90,8 +90,8 @@ class Authenticator(object):
     @defer.inlineCallbacks
     def authenticate_request(self, request, content):
         json_request = {
-            "method": request.method,
-            "uri": request.uri,
+            "method": request.method.decode('ascii'),
+            "uri": request.uri.decode('ascii'),
             "destination": self.server_name,
             "signatures": {},
         }
@@ -252,7 +252,7 @@ class BaseFederationServlet(object):
                     by the callback method. None if the request has already been handled.
             """
             content = None
-            if request.method in ["PUT", "POST"]:
+            if request.method in [b"PUT", b"POST"]:
                 # TODO: Handle other method types? other content types?
                 content = parse_json_object_from_request(request)
 
@@ -386,7 +386,7 @@ class FederationStateServlet(BaseFederationServlet):
         return self.handler.on_context_state_request(
             origin,
             context,
-            query.get("event_id", [None])[0],
+            parse_string_from_args(query, "event_id", None),
         )
 
 
@@ -397,7 +397,7 @@ class FederationStateIdsServlet(BaseFederationServlet):
         return self.handler.on_state_ids_request(
             origin,
             room_id,
-            query.get("event_id", [None])[0],
+            parse_string_from_args(query, "event_id", None),
         )
 
 
@@ -405,14 +405,12 @@ class FederationBackfillServlet(BaseFederationServlet):
     PATH = "/backfill/(?P<context>[^/]*)/"
 
     def on_GET(self, origin, content, query, context):
-        versions = query["v"]
-        limits = query["limit"]
+        versions = [x.decode('ascii') for x in query[b"v"]]
+        limit = parse_integer_from_args(query, "limit", None)
 
-        if not limits:
+        if not limit:
             return defer.succeed((400, {"error": "Did not include limit param"}))
 
-        limit = int(limits[-1])
-
         return self.handler.on_backfill_request(origin, context, versions, limit)
 
 
@@ -423,7 +421,7 @@ class FederationQueryServlet(BaseFederationServlet):
     def on_GET(self, origin, content, query, query_type):
         return self.handler.on_query_request(
             query_type,
-            {k: v[0].decode("utf-8") for k, v in query.items()}
+            {k.decode('utf8'): v[0].decode("utf-8") for k, v in query.items()}
         )
 
 
@@ -630,14 +628,14 @@ class OpenIdUserInfo(BaseFederationServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, origin, content, query):
-        token = query.get("access_token", [None])[0]
+        token = query.get(b"access_token", [None])[0]
         if token is None:
             defer.returnValue((401, {
                 "errcode": "M_MISSING_TOKEN", "error": "Access Token required"
             }))
             return
 
-        user_id = yield self.handler.on_openid_userinfo(token)
+        user_id = yield self.handler.on_openid_userinfo(token.decode('ascii'))
 
         if user_id is None:
             defer.returnValue((401, {