421 misdirected request

diff --git source/common/router/config_impl.cc source/common/router/config_impl.cc
index ae92edeab..3801e0d48 100644
--- source/common/router/config_impl.cc
+++ source/common/router/config_impl.cc
@@ -1310,17 +1310,30 @@ const VirtualHostImpl* RouteMatcher::findVirtualHost(const Http::RequestHeaderMa
   return default_virtual_host_.get();
 }

+const MisdirectedRequest MisdirectedRequestRoute::REDIRECTOR;
+const std::shared_ptr<const MisdirectedRequestRoute> MISDIRECTED_REQUEST_ROUTE{
+  new MisdirectedRequestRoute()
+};
+
 RouteConstSharedPtr RouteMatcher::route(const RouteCallback& cb,
                                         const Http::RequestHeaderMap& headers,
                                         const StreamInfo::StreamInfo& stream_info,
                                         uint64_t random_value) const {
-
   const VirtualHostImpl* virtual_host = findVirtualHost(headers);
   if (virtual_host) {
     return virtual_host->getRouteFromEntries(cb, headers, stream_info, random_value);
-  } else {
+  }
+
+  ENVOY_LOG_MISC(info, "virtual host lookup miss");
+  switch (stream_info.protocol().value_or(Http::Protocol::Http10)) {
+  case Http::Protocol::Http2:
+  case Http::Protocol::Http3:
+    ENVOY_LOG_MISC(info, "returning misdirected route");
+    return MISDIRECTED_REQUEST_ROUTE;
+  default: /* no-op */
     return nullptr;
   }
+
 }

 const SslRedirector SslRedirectRoute::SSL_REDIRECTOR;
diff --git source/common/router/config_impl.h source/common/router/config_impl.h
index d5f51ec19..39d592913 100644
--- source/common/router/config_impl.h
+++ source/common/router/config_impl.h
@@ -108,6 +108,33 @@ private:
   static const SslRedirector SSL_REDIRECTOR;
 };

+class MisdirectedRequest : public DirectResponseEntry {
+public:
+  // Router::DirectResponseEntry
+  void finalizeResponseHeaders(Http::ResponseHeaderMap&,
+                               const StreamInfo::StreamInfo&) const override {}
+  std::string newPath(const Http::RequestHeaderMap&) const override { return EMPTY_STRING; }
+  void rewritePathHeader(Http::RequestHeaderMap&, bool) const override {}
+  Http::Code responseCode() const override { return Http::Code::MisdirectedRequest; }
+  const std::string& responseBody() const override { return EMPTY_STRING; }
+  const std::string& routeName() const override { return EMPTY_STRING; }
+};
+
+class MisdirectedRequestRoute : public Route {
+public:
+  // Router::Route
+  const DirectResponseEntry* directResponseEntry() const override { return &REDIRECTOR; }
+  const RouteEntry* routeEntry() const override { return nullptr; }
+  const Decorator* decorator() const override { return nullptr; }
+  const RouteTracing* tracingConfig() const override { return nullptr; }
+  const RouteSpecificFilterConfig* perFilterConfig(const std::string&) const override {
+    return nullptr;
+  }
+
+private:
+  static const MisdirectedRequest REDIRECTOR;
+};
+
 /**
  * Implementation of CorsPolicy that reads from the proto route and virtual host config.
  */