TCP IP Illustrated

They should reply to a client request consisting of a

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:] Finger service for arbitrary addresses on is not supported. If you wish to send electronic mail, valid addresses are "PRESIDENT@WHITEHOUSE.GOV", and "VICEPRESIDENT@WHITEHOUSE.GOV" [] Another possibility is for an organization to implement a firewall gateway: a router between the organization and the Internet that filters out (i.e., discards) certain IP datagrams. ([Cheswick and Bellovin 1994] discuss firewall gateways in detail.) The firewall gateway can be configured to discard incoming datagrams that are TCP segments for port 79. In this case the Finger client times out after about 75 seconds. There are additional options for the Finger server, and for the Unix finger client. Refer to RFC 1288 and the finger(l) manual page for the details. RFC 1288 states that vending machines with TCP/IP connections that provide a Finger server should reply to a client request consisting of a blank line with a list of all items currently available. They should reply to a client request consisting of a name with a count or list of available items for that product. 30.3 Whois Protocol The Whois protocol is another information service. Although any site can provide a Whois server, the one at the InterNIC,, is most commonly used. This server maintains information about all registered DNS domains and many system administrators responsible for systems connected to the Internet. (Another server is provided at, but contains information only about the MILNET.) Unfortunately the information can be out of data or incomplete. RFC 954 [Harrenstien, Stahl, and Feinler 1985] documents the Whois service. From a protocol perspective, the Whois server has a well-known TCP port of 43. It accepts connection requests from clients, and the client sends a one-line query to the server. The server responds with whatever information is available and then closes the connection. The requests and replies are transmitted using NVT ASCII. This is almost identi...
View Full Document

Ask a homework question - tutors are online