CHARGEN

The Character Generator Protocol (CHARGEN) is a service of the defined in RFC 864 in 1983 by Jon Postel. It is intended for testing, debugging, and measurement purposes. The protocol is rarely used, as its design flaws allow ready misuse.

A host may connect to a server that supports the Character Generator Protocol on either (TCP) or (UDP) port number 19. Upon opening a TCP connection, the server starts sending arbitrary characters to the connecting host and continues until the host closes the connection. In the UDP implementation of the protocol, the server sends a UDP datagram containing a random number (between 0 and 512) of characters every time it receives a datagram from the connecting host. Any data received by the server is discarded.

On most UNIX-like operating systems, a CHARGEN server is built into the inetd or xinetd daemon. The CHARGEN service is usually not enabled by default. It may be enabled by adding the following lines to the file /etc/inetd.conf and telling inetd to reload its configuration:

The CHARGEN service may be used as a source of a byte-stream for debugging TCP network code for proper bounds checking and buffer management. It may also be a source of generic payload for bandwidth measurement and/or QoS fine-tuning. Although consideration must be given if hardware compression is active, as the output from the CHARGEN service is easily and efficiently compressed. This compression can cause bandwidth tests to report the size of the data after decompression, instead of the actual amount of data which passed the wire.

A typical CHARGEN service session looks like this: The user connects to the host using a telnet client. The user receives a stream of bytes. Although the specific format of the output is not prescribed by RFC 864, the recommended pattern (and a de facto standard) is shifted lines of 72 ASCII characters repeating.

...
Wikipedia