# DNS cache settings[edit](https://github.com/elastic/elasticsearch/edit/6.0/docs/reference/setup/sysconfig/dns-cache.asciidoc "Edit this page on GitHub") Elasticsearch runs with a security manager in place. With a security manager in place, the JVM defaults to caching positive hostname resolutions indefinitely. If your Elasticsearch nodes rely on DNS in an environment where DNS resolutions vary with time (e.g., for node-to-node discovery) then you might want to modify the default JVM behavior. This can be modified by adding[`networkaddress.cache.ttl=<timeout>`](http://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html) to your [Java security policy](http://docs.oracle.com/javase/8/docs/technotes/guides/security/PolicyFiles.html). Any hosts that fail to resolve will be logged. Note also that with the Java security manager in place, the JVM defaults to caching negative hostname resolutions for ten seconds. This can be modified by adding [`networkaddress.cache.negative.ttl=<timeout>`](http://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html) to your [Java security policy](http://docs.oracle.com/javase/8/docs/technotes/guides/security/PolicyFiles.html). > DNS相关知识