In other cases, there may be a need to change the URL of a particular resource on every request, usually by adding a "cachebuster" string to the URL. If this content is declared cacheable by a server for a significant freshness lifetime, these entries can crowd out legitimate entries in a cache. While mod_cache provides a CacheIgnoreURLSessionIdentifiers directive, this directive should be used with care to ensure that downstream proxy or browser caches aren't subjected to the same denial of service issue.