Remote Connectivity

The Saigon CTT

Remote
Connectivity


The Saigon CTT

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Objectives
 Explain :
telnet
rsh
ssh
 Configure FTP


The Saigon CTT

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Telnet
 Telnet is used to communicate to a host
through telnet protocol on default port 23
 It operates on client/server basic. The client
requires an account on the server to login
 Most telnet servers will not allow you
login as root because of security. You can
login as normal user and su to root

The Saigon CTT

 Telnet
 telnet is insecure protocol : username and
password send from client to server across
network in clear text

 why people still use it ? - telnet can be used
for debugging text based protocol : HTTP,
SMTP and POP


The Saigon CTT



Relevant File - ~/.telnetrc

 When users has .telnetrc file in their
home directories, telnet will execute the
commands listed in this file.
# this is a comment
saigonctt send ayt
DEFAULT environ export USER


The Saigon CTT



Telnet Commands
 Command Format :
telnet [IP address|host name] [port]

 If telnet is executed without options, it will be
started in command mode with prompt
“telnet>”
 You can change to command mode by
“Ctrl-]” after connected.


The Saigon CTT



Telnet Commands
?, h, help

Lists commands with description

<command> ?

More information of command (arg)

open <IP address> Open connection to the IP address or host name
close = quit

Terminates connection from client

logout

Requests server to terminate the connection

send

Send a special character sequence to the server

status

A brief status report of telnet

…
( See #man telnet for more commands )


The Saigon CTT

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The r Commands
 There are 3 programs :
rlogin

Remote login

rsh

Remote shell executes command

rcp

Remote copy

 Password NOT required if following files
are configured:
/etc/hosts.equiv

(system-wide)

$HOME/.rhosts

(per-user)

( Entry : [+|-] [hostname] [username] )


The Saigon CTT

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The r Commands
 rlogin :

similar to telnet

rlogin [-l username] <hostname>

 rsh

: executes cmd on remote host

rsh [-l username] <hostname> <cmd>
Shell meta-characters can be used in <cmd> To have rsh
interpret the meta-characters on remote machine, put
`quotation mark around them. If not quotes,metacharacters are interpreted on local machine :
# rsh –l minh saigonctt “cat ~/file” > local_file
# rsh –l minh saigonctt “cat ~/file” “>” remote_file


The Saigon CTT

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The r Commands
 rcp : copy files between machines
rcp <dir> <remote username>@<hostname>:<dir>
rcp <remote username>@<hostname>:<dir> <dir>

 Example :
rcp /home/file minh@saigonctt:/backup
rcp minh@saigonctt:/backup/file

/home

rcp -r /etc minh@saigonctt:/backup/etc
rcp –p /etc minh@saigonctt:/backup/etc


The Saigon CTT

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Security of r Commands
 centers around the idea of trusted users
and hosts , NOT password authentication.
• Trusted hosts are also known as equivalent hosts
• If NO hosts.equiv is present, NO hosts are trusted
• The .rhosts file is used to control access to an
individual user account
• It grant/denies password-free access to an individual
user account by means of .rhosts
• hosts.equiv does NOT work with root account
but .rhosts does


The Saigon CTT



SSH – Secure Shell
 SSH originally authored by Tatu Ylonen in
Finland, replacement for telnet,
rlogin, rsh, rcp
 Everything SSH send across network is
encrypted. SSH has become de-factor
standard for remote connection
 SSH can hanlde X connection

The Saigon CTT

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SSH Features
 Strong authentication with RSA, SecurID,
S/Key, Kerberos and TIS
 Secure X11 sessions
 Arbitrary TCP/IP ports can be redirect
through the encrypted channel in both
directions
 For forwarding, ssh captures on port 6010
 Optional compression of all data with gzip
 Complete replacement for rlogin, rsh, rcp


The Saigon CTT

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Component of SSH1
sshd

Server

ssh

Client

scp

Sercure copy files, replaces rcp

ssh-keygen

Creates RSA keys (host key and
authentication keys)

ssh-agent

Authetication agent, used to hold
RSA keys for authentication

ssh-add

Used to register new key with the
agent

make-ssh-known-hosts Used to create
/etc/ssh/ssh_known_hosts file


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Component of SSH2
sshd2

Server

ssh2

Client

sftp-server2

SFTP Server (executed by
sshd2)

sftp2
scp2

SFTP Client (need ssh2)
Sercure copy files, replaces rcp


The Saigon CTT

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Component of SSH2
ssh-keygen2

The utility for generating keys

ssh-agent2

Authetication agent, used to hold
RSA keys for authentication

ssh-add2

Add identifier to the authentication
agent

ssh-askpass2 X11 utility for querying password


The Saigon CTT

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SSH2 Changes
 SSH has been 98% rewritten
 Supports other key-exchange methods
besides RSA : Diffie-Hellman key exchange
 Supports for DSA and other public key
algorithms besides RSA


The Saigon CTT

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SSH2 Changes
 New added features : sftp , the secure file
transfer protocol
 More secure and allows integration into
public key infrastrures

 Supports “subsystems”, platformindependent module, built-in SOCKS, …


The Saigon CTT

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Install SSH1 – from OpenSSH
 Because of legal reasons, SSH is not included by
default in Linux. You can download and install from
source code or from OpenSSH
 OpenSSH suite includes :
• ssh (replaces telnet and rlogin)
• scp (replaces rcp)
• sftp (replaces ftp)


The Saigon CTT

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Install SSH1 – from OpenSSH
 Server : openssh-server-xxx.rpm
(sshd, sshd_config, sftp-server,
...)
 Client : openssh-clients-xxx.rpm
(ssh, ssh_config, sftp, ...)
 Addtion tools : openssh-xxx.rpm
(scp, ssh-keygen, ...)