Trivial Protocols CS-328 Dick Steflik

What’s a Protocol The rules that govern the exchange of information between to hosts –when a dignitary visits a foreign country there are certain rules of protocol that they must follow –when you meet the Queen of Great Britain you bow or curtsey

more specifically… Communications rules –who initiates the exchange –who terminates the exchange –what order things are done in finite state machine model –option negotiation

DayTime RFC 868, RFC 867 TCP and UDP port 13 client connects to port 13 –server returns date/time and closes connection

Echo RFC 862 TCP and UDP well known port 7 TCP Client opens connection on port 7 –Client sends data –server echos data back –repeat prev two steps –client closes connection

Echo UDP Client connects and sends data –host receives and immediately returns datagram

Finger Retrieve user information from remote host RFC 1288 well known TCP port 79 Client opens connection on port 79 –client sends finger query –remote host runs query, returns data and closes connection

Finger Queries –{Q1} ::= [{W} | {W} {S} {U} ] {C} –{Q2} ::= [{W} {S} ] [{U} {H} {C} –{U} ::= username –{H} –{W} ::= /W –{S} ::= | {S} –{C} ::=

Finger Remote User Interface Program (RUIP) –program on remote host that performs finger queries –may be turned off in TCP/IP config –may be configured to return limited info on user for security purposes –format may be differant on various platforms

Finger Security –many sites don’t fun finger servers a bug in the original finger left a hole through which unfriendly and unnatural acts could be done – Internet Worm gained machine access via the finger bug –some sites run a finger server that just returns a textual message

Post Office Protocol (POP3) Used in conjunction with anSMTP Host –SMTP Host sends and receives for remote users, POP allows users to retreive their mail from the host. –SMTP stores mail for unconnected hosts RFC 1730 TCP Port 110

POP3 protocol is relatively simple –connect to port 110 of remote host read back a response check for OK or ERR over and over again –close the connection

POP3 - State Machine AuthAuthTransactionUpdate USER PASS Commands QUIT

POP3 Commands –USER name terminate with identifies the user/mail drop name –PASS string user password usually the same as the user’s logon password –STAT request number of messages on server and size of mail drop

POP3 (Commands) –LIST return a list of all msgs on server –format msg size –LIST [msg_no] request size of msg_no –format msg_no size –RETR msg_no return the message identified by msg_no

POP3 (Commands) –DELE msg_no delete msg_no from server happens in UPDATE State –NOOP nothing except a positive reply from server –RSET reset all deletions pending on server –QUIT quit session, UPDATE, enter AUTH1 State