diff --git a/changelog.d/5447.misc b/changelog.d/5447.misc
new file mode 100644
index 000000000000..dd520684044a
--- /dev/null
+++ b/changelog.d/5447.misc
@@ -0,0 +1 @@
+Update federation_client dev script to support `.well-known` and work with python3.
diff --git a/scripts-dev/federation_client.py b/scripts-dev/federation_client.py
index e0287c8c6ccf..41e7b244187a 100755
--- a/scripts-dev/federation_client.py
+++ b/scripts-dev/federation_client.py
@@ -21,7 +21,8 @@
 import base64
 import json
 import sys
-from urlparse import urlparse, urlunparse
+
+from six.moves.urllib import parse as urlparse
 
 import nacl.signing
 import requests
@@ -145,7 +146,7 @@ def request_json(method, origin_name, origin_key, destination, path, content):
 
     for key, sig in signed_json["signatures"][origin_name].items():
         header = "X-Matrix origin=%s,key=\"%s\",sig=\"%s\"" % (origin_name, key, sig)
-        authorization_headers.append(bytes(header))
+        authorization_headers.append(header.encode("ascii"))
         print("Authorization: %s" % header, file=sys.stderr)
 
     dest = "matrix://%s%s" % (destination, path)
@@ -250,7 +251,7 @@ def read_args_from_config(args):
 
 class MatrixConnectionAdapter(HTTPAdapter):
     @staticmethod
-    def lookup(s):
+    def lookup(s, skip_well_known=False):
         if s[-1] == ']':
             # ipv6 literal (with no port)
             return s, 8448
@@ -263,19 +264,51 @@ def lookup(s):
                 raise ValueError("Invalid host:port '%s'" % s)
             return out[0], port
 
+        # try a .well-known lookup
+        if not skip_well_known:
+            well_known = MatrixConnectionAdapter.get_well_known(s)
+            if well_known:
+                return MatrixConnectionAdapter.lookup(
+                    well_known, skip_well_known=True
+                )
+
         try:
             srv = srvlookup.lookup("matrix", "tcp", s)[0]
             return srv.host, srv.port
         except Exception:
             return s, 8448
 
+    @staticmethod
+    def get_well_known(server_name):
+        uri = "https://%s/.well-known/matrix/server" % (server_name, )
+        print("fetching %s" % (uri, ), file=sys.stderr)
+
+        try:
+            resp = requests.get(uri)
+            if resp.status_code != 200:
+                print("%s gave %i" % (uri, resp.status_code), file=sys.stderr)
+                return None
+
+            parsed_well_known = resp.json()
+            if not isinstance(parsed_well_known, dict):
+                raise Exception("not a dict")
+            if "m.server" not in parsed_well_known:
+                raise Exception("Missing key 'm.server'")
+            new_name = parsed_well_known['m.server']
+            print("well-known lookup gave %s" % (new_name, ), file=sys.stderr)
+            return new_name
+
+        except Exception as e:
+            print("Invalid response from %s: %s" % (uri, e, ), file=sys.stderr)
+        return None
+
     def get_connection(self, url, proxies=None):
-        parsed = urlparse(url)
+        parsed = urlparse.urlparse(url)
 
         (host, port) = self.lookup(parsed.netloc)
         netloc = "%s:%d" % (host, port)
         print("Connecting to %s" % (netloc,), file=sys.stderr)
-        url = urlunparse(
+        url = urlparse.urlunparse(
             ("https", netloc, parsed.path, parsed.params, parsed.query, parsed.fragment)
         )
         return super(MatrixConnectionAdapter, self).get_connection(url, proxies)