TCP IP Illustrated

that many administrators consider private section 3

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 finger Trying ... 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...
View Full Document

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.

Ask a homework question - tutors are online