Telnet Options

Last Updated

  • 2022-03-16

Available Formats

Telnet Options

Registration Procedure(s)

  • IETF Review

Reference

  • RFC 855: Telnet Option Specifications

Note

The Telnet Protocol has a number of options that may be negotiated. These options are listed here. "Internet Official Protocol Standards" (STD 1) provides more detailed information.

Available Formats

Options Name Reference
0 Binary Transmission RFC 856
1 Echo RFC 857
2 Reconnection NIC 15391 of 1973
3 Suppress Go Ahead RFC 858
4 Approx Message Size Negotiation NIC 15393 of 1973
5 Status RFC 859
6 Timing Mark RFC 860
7 Remote Controlled Trans and Echo RFC 726
8 Output Line Width NIC 20196 of August 1978
9 Output Page Size NIC 20197 of August 1978
10 Output Carriage-Return Disposition RFC 652
11 Output Horizontal Tab Stops RFC 653
12 Output Horizontal Tab Disposition RFC 654
13 Output Formfeed Disposition RFC 655
14 Output Vertical Tabstops RFC 656
15 Output Vertical Tab Disposition RFC 657
16 Output Linefeed Disposition RFC 658
17 Extended ASCII RFC 698
18 Logout RFC 727
19 Byte Macro RFC 735
20 Data Entry Terminal RFC 1043; RFC 732
21 SUPDUP RFC 736; RFC 734
22 SUPDUP Output RFC 749
23 Send Location RFC 779
24 Terminal Type RFC 1091
25 End of Record RFC 885
26 TACACS User Identification RFC 927
27 Output Marking RFC 933
28 Terminal Location Number RFC 946
29 Telnet 3270 Regime RFC 1041
30 X.3 PAD RFC 1053
31 Negotiate About Window Size RFC 1073
32 Terminal Speed RFC 1079
33 Remote Flow Control RFC 1372
34 Linemode RFC 1184
35 X Display Location RFC 1096
36 Environment Option RFC 1408
37 Authentication Option RFC 2941
38 Encryption Option RFC 2946
39 New Environment Option RFC 1572
40 TN3270E RFC 2355
41 XAUTH Rob Earhart
42 CHARSET RFC 2066
43 Telnet Remote Serial Port (RSP) Robert Barnes
44 Com Port Control Option RFC 2217
45 Telnet Suppress Local Echo Wirt Atmar
46 Telnet Start TLS Michael Boe
47 KERMIT RFC 2840
48 SEND-URL David Croft
49 FORWARD_X Jeffrey Altman
50-137 Unassigned Internet Assigned Numbers Authority
138 TELOPT PRAGMA LOGON Steve McGregory
139 TELOPT SSPI LOGON Steve McGregory
140 TELOPT PRAGMA HEARTBEAT Steve McGregory
141-254 Unassigned
255 Extended-Options-List RFC 861

Telnet Authentication Types (Option 37)

Registration Procedure(s)

  • First Come First Served

Reference

Command

Registration Procedure(s)

  • First Come First Served

Reference

Available Formats

Command Description Reference
0 IS RFC 2941
1 SEND RFC 2941
2 REPLY RFC 2941
3 NAME RFC 2941

Types

Registration Procedure(s)

  • First Come First Served

Reference

Available Formats

Type Description Reference
0 NULL RFC 2941
1 KERBEROS_V4 RFC 2941
2 KERBEROS_V5 RFC 2942
3 SPX RFC 2941[1]
4 MINK RFC 2941[1]
5 SRP RFC 2944
6 RSA (also used by SRA) RFC 2941
7 SSL RFC 2941
8-9 Unassigned Internet Assigned Numbers Authority
10 LOKI RFC 2941[1]
11 SSA Steven Schoch
12 KEA_SJ RFC 2951
13 KEA_SJ_INTEG RFC 2951
14 DSS RFC 2943
15 NTLM Louis Kahn[1]

KERBEROS_V4 Telnet Authentication Type (Type 1)

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 1411: Telnet Authentication: Kerberos Version 4

Available Formats

Suboption Command Reference
0 AUTH RFC 1411
1 REJECT RFC 1411
2 ACCEPT RFC 1411
3 CHALLENGE RFC 1411
4 RESPONSE RFC 1411
5 FORWARD Derrick Brashear
6 FORWARD-ACCEPT Derrick Brashear
7 FORWARD-REJECT Derrick Brashear
8 EXP Thomas Wu
9 PARAMS Thomas Wu

KERBEROS_V5 Telnet Authentication Type (Type 2)

Registration Procedure(s)

  • Specification Required

Expert(s)

  • Unassigned

Reference

  • RFC 2942: Telnet Authentication: Kerberos Version 5

Available Formats

Suboption Command Reference
0 AUTH RFC 2942
1 REJECT RFC 2942
2 ACCEPT RFC 2942
3 RESPONSE RFC 2942
4 FORWARD RFC 2942
5 FORWARD_ACCEPT RFC 2942
6 FORWARD-REJECT RFC 2942

SRP Telnet Authentication Type (Type 5)

Registration Procedure(s)

  • Specification Required

Expert(s)

  • Unassigned

Reference

Available Formats

Suboption Command Reference
0 AUTH RFC 2944
1 REJECT RFC 2944
2 ACCEPT RFC 2944
3 CHALLENGE RFC 2944
4 RESPONSE RFC 2944
5-7 Unassigned RFC 2944
8 EXP RFC 2944
9 PARAMS RFC 2944

KEA_SJ (Type 12) and KEA_SJ_INTEG (Type 13) Authentication Types

Registration Procedure(s)

  • Specification Required

Expert(s)

  • Unassigned

Reference

  • RFC 2951: TELNET Authentication Using KEA and SKIPJACK

Available Formats

Suboption Command Reference
1 KEA_CERTA_RA RFC 2951
2 KEA_CERTB_RB_IVB_NONCEB RFC 2951
3 KEA_IVA_RESPONSEB_NONCEA RFC 2951
4 KEA_RESPONSEA RFC 2951

DSS Authentication Type (Type 14)

Registration Procedure(s)

  • Specification Required

Expert(s)

  • Unassigned

Reference

  • RFC 2943: TELNET Authentication Using DSA

Available Formats

Suboption Command Reference
1 DSS_INITIALIZE RFC 2943
2 DSS_TOKENBA RFC 2943
3 DSS_CERTA_TOKENAB RFC 2943
4 DSS_CERTB_TOKENBA2 RFC 2943

Telnet Encryption Types (Option 38)

Registration Procedure(s)

  • First Come First Served

Reference

Note

In the Telnet Encryption commands and types RFC 2946 there have been various implementations in several widely distributed versions of Telnet (e.g., at MIT, Stanford, and Columbia). Originally, only two encryption types were specified. Additional encryption types have been defined and are listed below. Additions to the list are registered by the IANA and documented here.

Command

Registration Procedure(s)

  • First Come First Served

Reference

Available Formats

Command Description Reference
0 IS RFC 2946
1 SUPPORT RFC 2946
2 REPLY RFC 2946
3 START RFC 2946
4 END RFC 2946
5 REQUEST-START RFC 2946
6 REQUEST-END RFC 2946
7 ENC_KEYID RFC 2946
8 DEC_KEYID RFC 2946

Types

Registration Procedure(s)

  • First Come First Served

Reference

Available Formats

Type Description Reference
0 NULL RFC 2946
1 DES_CFB64 RFC 2946
2 DES_OFB64 RFC 2946
3 DES3_CFB64 RFC 2946
4 DES3_OFB64 RFC 2946
5-7 Unassigned Internet Assigned Numbers Authority
8 CAST5_40_CFB64 RFC 2946
9 CAST5_40_OFB64 RFC 2946
10 CAST128_CFB64 RFC 2946
11 CAST128_OFB64 RFC 2946
12 AES_CCM S. Josefsson

DES_CFB64 Telnet Encryption Type (Type 1)

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2952: Telnet Encryption: DES 64 bit Cipher Feedback

Available Formats

Suboption Command Reference
1 CFB64_IV RFC 2952
2 CFB64_IV_OK RFC 2952
3 CFB64_IV_BAD RFC 2952

DES_OFB64 Telnet Encryption Type (Type 2)

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2953: Telnet Encryption: DES 64 bit Output Feedback

Available Formats

Suboption Command Reference
1 OFB64_IV RFC 2953
2 OFB64_IV_OK RFC 2953
3 OFB64_IV_BAD RFC 2953

DES3_CFB64 Telnet Encryption Type (Type 3)

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2947: Telnet Encryption: DES3 64 bit Cipher Feedback

Available Formats

Suboption Command Reference
1 CFB64_IV RFC 2947
2 CFB64_IV_OK RFC 2947
3 CFB64_IV_BAD RFC 2947

DES3_OFB64 Telnet Encryption Type (Type 4)

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2948: Telnet Encryption: DES3 64 bit Output Feedback

Available Formats

Suboption Command Reference
1 OFB64_IV RFC 2948
2 OFB64_IV_OK RFC 2948
3 OFB64_IV_BAD RFC 2948

CAST5_40_CFB64 (Type 8) and CAST128_CFB64 (Type 10) Telnet Encryption Types

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2950: Telnet Encryption: CAST-128 64 bit Cipher Feedback

Available Formats

Suboption Command Reference
1 CFB64_IV RFC 2950
2 CFB64_IV_OK RFC 2950
3 CFB64_IV_BAD RFC 2950

CAST5_40_OFB64 (Type 9) and CAST128_OFB64 (Type 11) Telnet Encryption Types

Registration Procedure(s)

  • First Come First Served

Reference

  • RFC 2949: Telnet Encryption: CAST-128 64 bit Output Feedback

Available Formats

Suboption Command Reference
1 OFB64_IV RFC 2949
2 OFB64_IV_OK RFC 2949
3 OFB64_IV_BAD RFC 2949

Contact Information

Name Contact URI Last Updated
David Croft david&infotrek.co.uk 1998-09
Derrick Brashear shadow&dementia.org 1995-01
Internet Assigned Numbers Authority iana&iana.org 2012-08
Jeffrey Altman jaltman&watsun.cc.columbia.edu 2000-01
Louis Kahn louisk&microsoft.com 1998-10
Michael Boe mboe&cisco.com 1998-06
Rob Earhart earhart+&cmu.edu 1995-04
Robert Barnes rab&stallion.oz.au 1997-07
S. Josefsson jas&extundo.com
http://josefsson.org/shishi/shishi.html#Telnet%20encryption%20with%20AES-CCM		 2003-11
Steve McGregory stevemc&pragmasys.com 1998-12
Steven Schoch schoch&sheba.arc.nasa.gov 1995-01
Thomas Wu tjw&stanford.edu 1998-09
Wirt Atmar atmar&aics-research.com 1998-06

Footnote

[1]

Authentication types never submitted to the IETF for consideration as an Internet standard.