Glossary: Endpoint, Application and Email Security

Host addresses (127.0.0.1, 0.0.0.0)

Also written: 127.0.0.1, 0.0.0.0, localhost, loopback address

127.0.0.1 is the loopback address. It means "this machine itself", so it is often used to run a test proxy, web server or DNS server that only the local computer can reach. 0.0.0.0 means "no specific address", and when a server listens on it, it means "every address on this machine".