/**
         * @param ttl
         */
        NegativeCacheEntry ( long ttl ) {
            super(ttl);
        }

    }

    private static final Logger log = LoggerFactory.getLogger(DfsImpl.class);
    private static final String DC_ENTRY = "dc";

    private CacheEntry<Map<String, CacheEntry<DfsReferralDataInternal>>> _domains = null; /*