Unformatted text preview: e provide only a brief overview of this complex
application, focusing on its use of the TCP/IP protocols.
Additionally we provide an overview of some Internet resource discovery tools. These are
tools to help us navigate our way around the Internet, searching for items whose location and
exact name we don't know. 30.2 Finger Protocol
The Finger protocol returns information on one or more users on a specified host. It's
commonly used to see if someone is currently logged on, or to figure out someone's login
name, to send them mail. RFC 1288 [Zimmerman 1991] specifies the protocol.
Many sites do not run a Finger server for two reasons. First, a programming error in an
earlier version of the server was one of the entry points used by the infamous Internet worm
of 1988. (RFC 1135 [Reynolds 1989] and [Curry 1992] describe the worm in more detail.)
Second, the Finger protocol can reveal detailed information on users (login names, phone
numbers, when they last logged in, etc.) that many administrators consider private. Section 3
of RFC 1288 details the security aspects of this service.
From a protocol perspective, the Finger server has a well-known port of 79. The client does
an active open to this port and sends a one-line query The server processes the query, sends
back the output, and closes the connection. The query and response are NVT ASCII, similar
to what we saw with FTP and SMTP.
While most Unix users access the Finger server using the finger(l) client, we'll start by using
the Telnet client to connect directly to the server and see the one-line commands issued by
the client. If the client query is an empty line (which in NVT ASCII is transmitted as a CR
followed by an LF), it is a request for information on all online users.
sun % telnet slip
Connected to slip. first three lines are output by Telnet client file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/other.htm (1 of 11) [12/09/2001 14.47.58] Chapter 30. Other TCP/IP Applications Escape character is
here we type RETURN as the Finger client comma...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12