added comment about why we don't return SERVFAIL due to an internal error in handling notify

git-svn-id: svn://bind10.isc.org/svn/bind10/branches/trac221@2334 e5f2f494-b856-4b98-b285-d166d9295462

src/bin/auth/auth_srv.cc

@@ -406,6 +406,11 @@ AuthSrvImpl::processNotify(const IOMessage& io_message, Message& message,
 
     // TODO check with the conf-mgr whether current server is the auth of the
     // zone
+
+    // In the code that follows, we simply ignore the notify if any internal
+    // error happens rather than returning (e.g.) SERVFAIL.  RFC 1996 is
+    // silent about such cases, but there doesn't seem to be anything we can
+    // improve at the primary server side by sending an error anyway.
     if (!is_notify_session_established_) {
         try {
             session_with_xfrin_.establish(NULL);