1. Remote Access http://en.wikipedia.org/wiki/Telnet The old, safe world:
telnet, rlogin, rsh, rcp

2. Telecommunications Network
Telnet
Telecommunications
Network

3. TELNET TELecommunication NETwork
A network protocol used on Internet or LAN connections
Developed in 1969 beginning with RFC 15
Standardized as IETF STD 8
One of the first Internet standards
The term telnet also refers to software which implements the client part of the protocol
TELNET clients have been available on most Unix systems for many, many years
Available for virtually all platforms
Most network equipment and OSs with a TCP/IP stack support some kind of TELNET service server for their remote configuration
Secure Shell has begun to dominate remote access for Unix-based machines.

4. TELNET "To telnet" sometimes used as a verb
Establish or use a TELNET or other interactive TCP connection
"To change your password, telnet to the server and run the passwd command"
Typically a user will be telneting to a Unix-like server system or a simple network device such as a switch
User might "telnet in from home to check his mail at school"
Use a telnet client to connect local computer to a server
Once the connection is established
Log in with his account information
Execute commands remotely on that computer
E.g. ls or cd
Client may also be used to make interactive raw-TCP sessions
When that option is not available, telnet sessions are equivalent to raw TCP as long as byte 255 never appears in the data
? What is byte 255 ?

5. Protocol details

6. Protocol details TELNET is a client-server protocol
Based on a reliable connection-oriented transport.
Typically TCP port 23
TELNET predates TCP/IP
Originally ran on NCP
The protocol has many extensions
Some adopted as Internet standards
IETF standards STD 27 through STD 32
Define various extensions
Most are extremely common.
Other extensions are on the IETF standards track as proposed standards

7. Security

8. Security TELNET initially developed in 1969
Most networked computers at the time:
Computer departments of academic institutions
Large private and government research facilities
Security originally not as much of a concern
Changed after the bandwidth explosion of the 1990s
Enencrypted alternatives made necessary
Rise in the number of people with access to the Internet
Number of people attempting to crack other people's servers

9. Security
Experts in computer security1 recommend that the use of TELNET for remote logins should be discontinued under all normal circumstances for the following reasons:
1SANS Institute, members of the comp.os.linux.security newsgroup

10. Security
TELNET, by default, does not encrypt any data sent over the connection (including passwords)
It is easy to eavesdrop on the communications
Easy to intercept ids and passwords
Anybody with access to a router, switch, or gateway located on the network between the two hosts where TELNET is being used:
Can intercept the packets
Obtain login and password information
Any of several common utilities
E.g. tcpdump and Wireshark

11. Security Most implementations of TELNET lack an authentication scheme
Cannot ensure that communication is carried out between the two desired hosts, and not intercepted in the middle
Commonly used TELNET daemons have several vulnerabilities discovered over the years

12. Security
Security-related shortcomings have seen the usage of the TELNET protocol drop rapidly
Especially on the public Internet,
In favor of a the ssh protocol
First released in 1995
SSH provides much of the functionality of telnet
Also has:
Strong encryption
Prevents sensitive data such as passwords from being intercepted
Public key authentication
Ensures that the remote computer is actually who it claims to be

13. Security As has happened with other early Internet protocols
Extensions to the TELNET protocol provide TLS security and SASL authentication that address many security issues
Most TELNET implementations do not support these extensions
Relatively little interest in implementing these
SSH is adequate for most purposes.
The main advantage of TLS-TELNET
Ability to use certificate-authority signed server certificates:
to authenticate a server host to a client that does not yet have the server key stored
SSH weakness:
User must trust the first session to a host when it has not yet acquired the server key

14. Current status

15. Current status TELNET clients are still used (as of the mid-2000s)
Often when diagnosing problems
Manually "talk" to other services without specialized client software
Sometimes used in debugging network services
an SMTP, IRC or HTTP server
Serves as a simple way to send commands to the server and examine the responses

16. Current status
Other software such as nc (netcat) or socat on Unix (or PuTTY on Windows) are finding greater favor with some system administrators for testing purposes
They can be called with arguments not to send any terminal control handshaking data
netcat does not distort the \377 octet
which allows raw access to TCP socket
unlike any standard-compliant TELNET software

17. Current status
TELNET is still very popular in enterprise networks to access host applications
IBM Mainframes
Typically in an internal secure environment
TELNET is still widely used for administration of network elements
Commissioning
Integration
Maintenance
of core network elements in mobile communication networks

18. Current status TELNET is also heavily used for Windows Vista
MUD games played over the Internet
talkers, MUSHes, MUCKs, MOOes
Resurgent BBS community
Windows Vista
Telnet.exe is no longer installed by default
Is still included as an installable feature

19. http://en.wikipedia.org/wiki/Remote_Shell Remote SHell
rsh
Remote SHell

20. Remote Shell
rsh (remote shell):
A command line computer program
Can execute shell commands
As another user
On another computer in a computer network
Remote system on which the rsh executes needs to be running the rshd daemon.
rsh uses well-known port TCP 514.
Note: rsh command shares the same name as another common UNIX utility, the restricted shell
First appeared in PWB/UNIX; in System V Release 4
Restricted shell is often located at /usr/lib/rsh.

21. Remote Shell
rsh originated as part of the BSD Unix operating system, along with rcp, as part of the rlogin package on 4.2BSD in 1983
rsh has been ported to other operating systems
rsh protocol is not secure for network use
Sends unencrypted information over the network
Some implementations also authenticate by sending unencrypted passwords over the network
rsh has largely been replaced by the very similar ssh (secure shell) program on untrusted networks like the internet

22. Remote Shell rsh example:
Execute the command mkdir testdir as user remoteuser on the computer host.example.com:
rsh -l remoteuser host.example.com "mkdir testdir"
After the command has finished rsh terminates
If no command is specified then rsh will log in on the remote system using rlogin
Network location of the remote computer is looked up using the Domain Name System

23. http://en.wikipedia.org/wiki/Rlogin Remote Login
rlogin
Remote Login

24. rlogin
rlogin is a Unix software utility that allows users to log in on another host via a network
Communicates via TCP port 513
First distributed as part of the 4.2BSD release
rlogin is also the name of the application layer protocol used by the software
part of the TCP/IP protocol suite
Authenticated users can act as if physically present at the computer
RFC 1258 states:
"The rlogin facility provides a remote-echoed, locally flow-controlled virtual terminal with proper flushing of output."
rlogin communicates with a daemon, rlogind, on the remote host.
rlogin is similar to the Telnet command
Not customizable
Can connect only to Unix hosts

25. rlogin rlogin most commonly deployed on corporate or academic networks
user account information is shared between all the Unix machines on the network
often using NIS
Deployments essentially trust most other machines (and the network infrastructure itself)
the rlogin protocol relies on this trust.
rlogind allows logins without password (where rlogind trusts a remote rlogin client)
if the remote host appears in the /etc/hosts.equiv file
if the user in question has a .rhosts file in their home directory

26. rlogin rlogin has several serious security problems:
All information is transmitted unencrypted
Including passwords!
.rlogin (or .rhosts) file is easy to misuse
Potentially allows anyone to login without a password
Many corporate system administrators prohibit .rlogin files
actively search their networks for offenders
Protocol partly relies on the remote party's rlogin client providing information honestly (including source port and source host name)
A corrupt client is able to forge this and gain access
rlogin protocol has no means of authenticating other machines' identities, or ensuring that the rlogin client on a trusted machine is the real rlogin client
Common practice of mounting users' home directories via NFS exposes rlogin to attack by means of fake .rhosts files
Any of NFS' security faults automatically plague rlogin

27. rlogin
Due to these serious problems rlogin is rarely used across untrusted networks (like the public internet)
Even in closed deployments it has fallen into relative disuse
many Unix and Linux distributions no longer including it by default
Many networks which formerly relied on rlogin and telnet
Replaced them with SSH and its rlogin-equivalent slogin

28. rlogin
Original Berkeley package which provides rlogin also features rcp and rsh
Share the hosts.equiv and .rhosts access-control scheme
Suffer from the same security problems
Do connect to a different daemon, rshd
ssh suite contains suitable replacements for both:
scp replaces rcp
ssh itself replaces both rlogin and rsh

29. http://en.wikipedia.org/wiki/Rcp_%28Unix%29 Remote Copy
rcp
Remote Copy

30. rcp rcp: the Unix ‘Remote CoPy' command
Command on the Unix used to remotely copy
Copy one or more files from one computer system to another
Typically uses
TCP/IP protocol
.rhosts file for authentication
Has been implemented to alternatively support Kerberos.
rcp is not secure for network use
Sends unencrypted information over the network
Largely replaced by the ssh-based utility scp
Etymology:
rcp is a member of the BSD unix family of 'r' (remote) commands
Name is a contraction of 'r' remote and 'cp' copy.

31. Summary Host of insecure remote commands
Developed before security was a major concern
May be okay for “internal” use
On “secure” networks
Overall:
Use modern secure alternatives