Trivial Protocols

1
Trivial Protocols

• CS-328
• Dick Steflik

2
Whats 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

3
more specifically

• Communications rules
• who initiates the exchange
• who terminates the exchange
• what order things are done in
• finite state machine model
• option negotiation

4
DayTime

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

5
Echo

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

6
Echo

• UDP Client connects and sends data
• host receives and immediately returns datagram

7
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

8
Finger

• Queries
• Q1 W W S U C
• Q2 W S U H C
• U username
• H _at_hostname _at_hostnameH
• W /W
• S ltspgt ltspgtS
• C ltcrlfgt

9
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

10
Finger

• Security
• many sites dont fun finger servers
• a bug in the original finger left a hole through
  which unfriendly and unnatural acts could be done
• 1988 - Internet Worm gained machine access via
  the finger bug
• some sites run a finger server that just returns
  a textual message

11
Post Office Protocol (POP3)

• Used in conjunction with anSMTP Host
• SMTP Host sends and receives e-mail for remote
  users, POP allows users to retreive their mail
  from the host.
• SMTP stores mail for unconnected hosts
• RFC 1730
• TCP Port 110

12
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

13
POP3 - State Machine
Commands
Auth
Auth
Transaction
Update
USER
PASS
QUIT
14
POP3

• Commands
• USER name
• terminate with ltcrlfgt
• identifies the user/mail drop name
• PASS string
• user password
• usually the same as the users logon password
• STAT
• request number of messages on server and size of
  mail drop

15
POP3 (Commands)

• LIST
• return a list ltcrlfgt 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

16
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