diff --git a/changelog.d/4497.feature b/changelog.d/4497.feature
new file mode 100644
index 0000000000..bda713adf9
--- /dev/null
+++ b/changelog.d/4497.feature
@@ -0,0 +1 @@
+Implement MSC1708 (.well-known routing for server-server federation)
\ No newline at end of file
diff --git a/tests/http/federation/test_matrix_federation_agent.py b/tests/http/federation/test_matrix_federation_agent.py
index 8257594fb8..53b52ace59 100644
--- a/tests/http/federation/test_matrix_federation_agent.py
+++ b/tests/http/federation/test_matrix_federation_agent.py
@@ -377,9 +377,8 @@ class MatrixFederationAgentTests(TestCase):
 
         self.mock_resolver.resolve_service.side_effect = lambda _: []
 
-        # hostnameendpoint does the lookup on the unicode value (getaddrinfo encodes
-        # it back to idna)
-        self.reactor.lookups[u"bücher.com"] = "1.2.3.4"
+        # the resolver is always called with the IDNA hostname as a native string.
+        self.reactor.lookups["xn--bcher-kva.com"] = "1.2.3.4"
 
         # this is idna for bücher.com
         test_d = self._make_get_request(b"matrix://xn--bcher-kva.com/foo/bar")
@@ -424,7 +423,7 @@ class MatrixFederationAgentTests(TestCase):
         self.mock_resolver.resolve_service.side_effect = lambda _: [
             Server(host=b"xn--trget-3qa.com", port=8443)  # târget.com
         ]
-        self.reactor.lookups[u"târget.com"] = "1.2.3.4"
+        self.reactor.lookups["xn--trget-3qa.com"] = "1.2.3.4"
 
         test_d = self._make_get_request(b"matrix://xn--bcher-kva.com/foo/bar")
 
diff --git a/tests/server.py b/tests/server.py
index ed2a046ae6..6adcc73f91 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -8,11 +8,10 @@ import attr
 from zope.interface import implementer
 
 from twisted.internet import address, threads, udp
-from twisted.internet._resolver import HostResolution
-from twisted.internet.address import IPv4Address
-from twisted.internet.defer import Deferred
+from twisted.internet._resolver import SimpleResolverComplexifier
+from twisted.internet.defer import Deferred, fail, succeed
 from twisted.internet.error import DNSLookupError
-from twisted.internet.interfaces import IReactorPluggableNameResolver
+from twisted.internet.interfaces import IReactorPluggableNameResolver, IResolverSimple
 from twisted.python.failure import Failure
 from twisted.test.proto_helpers import MemoryReactorClock
 from twisted.web.http import unquote
@@ -227,30 +226,16 @@ class ThreadedMemoryReactorClock(MemoryReactorClock):
 
     def __init__(self):
         self._udp = []
-        self.lookups = {}
+        lookups = self.lookups = {}
 
-        class Resolver(object):
-            def resolveHostName(
-                _self,
-                resolutionReceiver,
-                hostName,
-                portNumber=0,
-                addressTypes=None,
-                transportSemantics='TCP',
-            ):
+        @implementer(IResolverSimple)
+        class FakeResolver(object):
+            def getHostByName(self, name, timeout=None):
+                if name not in lookups:
+                    return fail(DNSLookupError("OH NO: unknown %s" % (name, )))
+                return succeed(lookups[name])
 
-                resolution = HostResolution(hostName)
-                resolutionReceiver.resolutionBegan(resolution)
-                if hostName not in self.lookups:
-                    raise DNSLookupError("OH NO")
-
-                resolutionReceiver.addressResolved(
-                    IPv4Address('TCP', self.lookups[hostName], portNumber)
-                )
-                resolutionReceiver.resolutionComplete()
-                return resolution
-
-        self.nameResolver = Resolver()
+        self.nameResolver = SimpleResolverComplexifier(FakeResolver())
         super(ThreadedMemoryReactorClock, self).__init__()
 
     def listenUDP(self, port, protocol, interface='', maxPacketSize=8196):