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CS4550 Computer Networks II
APPLICATIONS
TELNET Feit Chap 13FTP Feit Chap 14E-Mail Feit Chap 16
TELNETPURPOSE: Provide alphanumeric terminal
communication between two computers
INSTALLATION: Typically available as part of network
SW in W95, NT, unix
NETWORK SERVICES:
connection TCP
well known port 23
run from command prompt
TELNET ARCHITECTURE
Telnet Client
TCP TCP
Telnet SERVER
Application
Port 23
NVT
TCP Connection
Network Virtual Terminal (NVT)
Data Format : 8’th bit 0 ASCII 0 -127
Control Data: 8’th bit 1 ASCII 128-255
OPTIONS NEGOTIATION: (DO,WILL), (DO,WONT), (WILL,DO), (WILL,DON’T)
Option Codes: see Feit Table 13.3
Internet Assigned Numbers Authority,www.iana.org
Format : IAC request byte option code
Example:255 250 24
Means: Will terminal type 24
TELNET SESSIONCommand Format:
telnet hostname [port#]
Connecting to other ports example:
telnet cs.nps.navy.mil 25
220 cs.nps.navy.mil ESMTP Sendmail 8.9.2/8.9.2; Tue, 1 Feb 2000 09:18:09 -0800 PST)
HELO wolf
250 cs.nps.navy.mil Hello wolf.cs.nps.navy.mil [131.120.8.161], pleased to meet you
quit
221 cs.nps.navy.mil closing connection
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