--- a/testing/web-platform/tests/config.default.json
+++ b/testing/web-platform/tests/config.default.json
@@ -1,12 +1,12 @@
 {"host": "web-platform.test",
  "doc_root": null,
  "ws_doc_root": null,
- "external_host": null,
+ "host_ip": null,
  "ports":{"http":[8000, "auto"],
           "https":[8443],
           "ws":["auto"],
           "wss":["auto"]},
  "check_subdomains": true,
  "log_level":"debug",
  "bind_hostname": true,
  "ssl": {"type": "pregenerated",

--- a/testing/web-platform/tests/tools/serve/serve.py
+++ b/testing/web-platform/tests/tools/serve/serve.py
@@ -619,35 +619,33 @@ def get_ports(config, ssl_environment):
             else:
                 port = port
             rv[scheme].append(port)
     return rv
 
 
 
 def normalise_config(config, ports):
-    host = config["external_host"] if config["external_host"] else config["host"]
-    domains = get_subdomains(host)
+    domains = get_subdomains(config["host"])
     ports_ = {}
     for scheme, ports_used in ports.iteritems():
         ports_[scheme] = ports_used
 
     for key, value in domains.iteritems():
         domains[key] = ".".join(value)
 
-    domains[""] = host
+    domains[""] = config["host"]
 
     ports_ = {}
     for scheme, ports_used in ports.iteritems():
         ports_[scheme] = ports_used
 
     # make a (shallow) copy of the config and update that, so that the
     # normalized config can be used in place of the original one.
     config_ = config.copy()
-    config_["host"] = host
     config_["domains"] = domains
     config_["ports"] = ports_
     return config_
 
 
 def get_paths(config):
     return {"doc_root": config["doc_root"],
             "ws_doc_root": config["ws_doc_root"]}
@@ -655,16 +653,17 @@ def get_paths(config):
 
 def get_ssl_config(config, ssl_environment):
     external_domains = config["domains"].values()
     key_path, cert_path = ssl_environment.host_cert_path(external_domains)
     return {"key_path": key_path,
             "cert_path": cert_path,
             "encrypt_after_connect": config["ssl"]["encrypt_after_connect"]}
 
+
 def start(config, ssl_environment, routes, **kwargs):
     host = config["host"]
     ports = get_ports(config, ssl_environment)
     paths = get_paths(config)
     bind_hostname = config["bind_hostname"]
     ssl_config = get_ssl_config(config, ssl_environment)
 
     servers = start_servers(host, ports, paths, routes, bind_hostname, config,

--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/firefox.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/firefox.py
@@ -112,18 +112,18 @@ def executor_kwargs(test_type, server_co
     return executor_kwargs
 
 
 def env_extras(**kwargs):
     return []
 
 
 def env_options():
-    return {"host": "127.0.0.1",
-            "external_host": "web-platform.test",
+    return {"host_ip": "127.0.0.1",
+            "host": "web-platform.test",
             "bind_hostname": "false",
             "certificate_domain": "web-platform.test",
             "supports_debugger": True}
 
 
 def run_info_extras(**kwargs):
     return {"e10s": kwargs["gecko_e10s"],
             "headless": "MOZ_HEADLESS" in os.environ}

--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/servo.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/servo.py
@@ -47,18 +47,18 @@ def executor_kwargs(test_type, server_co
     return rv
 
 
 def env_extras(**kwargs):
     return []
 
 
 def env_options():
-    return {"host": "127.0.0.1",
-            "external_host": "web-platform.test",
+    return {"host": "web-platform.test",
+            "host_ip": "127.0.0.1",
             "bind_hostname": "false",
             "testharnessreport": "testharnessreport-servo.js",
             "supports_debugger": True}
 
 
 def update_properties():
     return ["debug", "os", "version", "processor", "bits"], None
 

--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/servodriver.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/servodriver.py
@@ -53,18 +53,18 @@ def executor_kwargs(test_type, server_co
     return rv
 
 
 def env_extras(**kwargs):
     return []
 
 
 def env_options():
-    return {"host": "127.0.0.1",
-            "external_host": "web-platform.test",
+    return {"host_ip": "127.0.0.1",
+            "host": "web-platform.test",
             "bind_hostname": "true",
             "testharnessreport": "testharnessreport-servodriver.js",
             "supports_debugger": True}
 
 
 def update_properties():
     return ["debug", "os", "version", "processor", "bits"], None
 

--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/environment.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/environment.py
@@ -134,19 +134,19 @@ class TestEnvironment(object):
 
         with open(default_config_path) as f:
             default_config = json.load(f)
 
         with open(local_config_path) as f:
             data = f.read()
             local_config = json.loads(data % self.options)
 
-        #TODO: allow non-default configuration for ssl
+        # TODO: allow non-default configuration for ssl
 
-        local_config["external_host"] = self.options.get("external_host", None)
+        local_config["host_ip"] = self.options.get("host_ip", None)
         local_config["ssl"]["encrypt_after_connect"] = self.options.get("encrypt_after_connect", False)
 
         config = serve.merge_json(default_config, local_config)
         config["doc_root"] = serve_path(self.test_paths)
 
         if not self.ssl_env.ssl_enabled:
             config["ports"]["https"] = [None]
 
@@ -211,25 +211,28 @@ class TestEnvironment(object):
 
     def ensure_started(self):
         # Pause for a while to ensure that the server has a chance to start
         for _ in xrange(20):
             failed = self.test_servers()
             if not failed:
                 return
             time.sleep(0.5)
-        raise EnvironmentError("Servers failed to start (scheme:port): %s" % ("%s:%s" for item in failed))
+        raise EnvironmentError("Servers failed to start: %s" %
+                               ", ".join("%s:%s" % item for item in failed))
 
     def test_servers(self):
         failed = []
+        host = self.config.get("host_ip") or self.config.get("host")
         for scheme, servers in self.servers.iteritems():
             for port, server in servers:
                 if self.test_server_port:
                     s = socket.socket()
                     try:
-                        s.connect((self.config["host"], port))
+                        s.connect((host, port))
                     except socket.error:
-                        failed.append((scheme, port))
+                        failed.append((host, port))
                     finally:
                         s.close()
 
                 if not server.is_alive():
                     failed.append((scheme, port))
+        return failed