The Ident Protocol, specified in RFC 1413, is an Internet protocol that helps identify the user of a particular TCP connection. One popular daemon program for providing the ident service is identd.

How Ident Works

The Ident Protocol is designed to work as a server daemon, on a user's computer, where it receives requests to a specified port, generally 113. The server will then send a specially designed response that identifies the username of the current user.

Usefulness of Ident

The usefulness of Ident is limited to circumstances when:

* The user connecting is not the administrator of the machine. This is only likely for shared machines using a suEXEC-like construction.
* The service trusts the administrator of the remote machine. This is only likely for hosts in a common security domain such as within a single organization.
* The server trusts that the remote host is the machine it claims to be. This is only easily arranged for hosts on a local area network or virtual network where all hosts on the network are trusted and new hosts cannot easily be added due to physical protection. For machines on remote networks it would require some form of DNS authentication which is uncommon.

Nonetheless Ident is widely used and considered useful by some. Dialup hosts or shared shell servers often provide it as a service to other systems to enable abuse to be tracked back to specific users.


The ident protocol is considered dangerous because it allows hackers to gain a list of usernames on a computer system which can later be used for attacks. A generally accepted solution to this is to set up a generic/generated identifier, returning node information or even gibberish (from the requesters point of view) rather than usernames.


Ident is important on IRC as a large number of people connect to IRC servers via bouncers which either serve multiple users or are hosted on shared servers. Some users also use clients on Unix shells. Without ident there would be no way to ban a single user of a bouncer from a channel or network without banning the entire host running the bouncer. The bouncer operator may also need this information to identify the abusive user. When an IRC server fails to get an identd response it has to fall back on the username given by the client. Ircds usually prefix usernames obtained directly from the client software with a tilde to indicate that they are not ident usernames and may be faked by the user (although with modern single-user home computers, the ident username itself may be set to whatever the user wants and is often returned by the same IRC client as the rest of the client information). Some IRC servers even go as far as blocking clients without an ident response , the main reason being that it makes it much harder to connect via an "open proxy" or a system where you have compromised a single account of some form but do not have root .

Special identds are used by those running large numbers of bouncers or a single bouncer that supports multiple users to allow bouncer usernames to be returned rather than simply the name of the user account on the system the bouncer is running under.

ee also

*Internet Relay Chat (IRC)
*File Transfer Protocol (FTP)
*Simple Mail Transfer Protocol (SMTP)
*Network News Transfer Protocol (NNTP)
*Secure Shell (SSH)


* RFC 912 - Authentication Service
* RFC 931 - Authentication Server
* Daniel J. Bernstein: [ TAP] - INTERNET DRAFT 1992
* Daniel J. Bernstein: [ Why TAP?] A White Paper, draft 3 920820
* RFC 1413 - Identification Protocol
* RFC 1414 - Identification MIB
* Peter Eriksson: [ TAPvsIDENT] 3 Nov 1993
* Damien Doligez: [ Why encrypt ident/TAP replies?] 1994.02.22

External links

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