Glossary: Secure Infrastructure and Zero Trust

Host addresses (127.0.0.1, 0.0.0.0)

Also written: 127.0.0.1, 0.0.0.0, loopback, loopback address, localhost

127.0.0.1 is the loopback address: the machine talking to itself, so a service bound to it can't be reached over the network. 0.0.0.0 in `ss` output means a service is listening on every network the server is connected to.