# WHATPORT(513)

## NAME

port 513 — rlogin — BSD rlogin — a remote shell session that trusts the client host instead of asking for a password.

Protocol: TCP  
IANA registry

## DESCRIPTION

rlogin, documented in RFC 1282, gives a terminal session much like Telnet, but its authentication is host-based: the server trusts a connection from a privileged source port if the client host and user appear in /etc/hosts.equiv or the target user's ~/.rhosts. That trust model is the reason it died — anyone who can spoof an address or compromise one trusted host inherits accounts everywhere. The traffic, including anything typed into the session, is unencrypted. UDP 513 is a different service entirely, rwho, which broadcasts who is logged in and the machine's load average.

## EXPOSURE

**Do not expose.** Cleartext interactive login with address-based trust — a .rhosts entry plus a spoofed or compromised peer is a remote shell. SSH replaced this in the 1990s.

## CHECK

```sh
nc -vz -w 3 TARGET 513
```

## SEE ALSO

- spec — [RFC 1282 — BSD Rlogin](https://www.rfc-editor.org/rfc/rfc1282.html) (rfc-editor.org)
- iana — [IANA Service Name and Transport Protocol Port Number Registry — 513](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=513) (iana.org)

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HTML: <https://whatport.net/513/> · JSON: <https://whatport.net/513.json> · full dataset: <https://whatport.net/ports.json>