Telnet Extended Options Standard

EXOP • Standard • Links EOR GMCP MCCP MMCP MNES MSDP MSLP MSSP MTTS

TELNET is currently limited to a total of 256 TELOPTS (TELNET OPTIONS) of which about a quarter are taken. While the growth of new TELOPTS is currently very slow it's hard to predict future growth. The TELNET protocol remains a solid framework to build upon.

The Telnet Extended Options Standard seeks to address this potential issue by reserving TELNET options ranging from 192 to 254 so they can be used to encode TELNET options as UTF-8 code points allowing for a total of 2,031,616 TELOPTS.

Telnet Options in the 128-191 range can be encoded as either 1 byte or 2 byte sequences without known compatibility issues. Telnet Options in the 192-254 range encoded as a 1 byte sequence should be detectable (due to the nature of the TELNET protocol) but there is a chance of unforseen false positives.

Any newly introduced TELNET OPTION should ideally be in the 64-191 range or in the 256+ range using UTF-8 encoding. In the case an invalid UTF-8 codepoint is found the TELNET handler should assume that it is dealing with a non-compliant TELNET implementation.

Bytes Codepoint bits Codepoint total First codepoint Last codepoint Byte 1 Byte 2 Byte 3 Byte 4 1 7 128 \u0000 \u00F7 0....... 2 11 2048 \u0080 \u07FF 110..... 10...... 3 16 65536 \u0800 \uFFFF 1110.... 10...... 10...... 4 21 2097152 \U010000 \U1FFFFF 11110... 10...... 10...... 10......

To aid in the orderly allocation of TELOPTS this specification will also try to document existing and new TELOPTS.

TELOPTS

Index Name Note 0 BINARY 1 ECHO 2 RCP 3 SGA 4 NAMS 5 STATUS 6 TIMINGMARK 7 RCTE 8 NAOL 9 NAOP 10 NAOCRD 11 NAOHTS 12 NAOHTD 13 NAOFFD 14 NAOVTS 15 NAOVTD 16 NAOLFD 17 XASCII 18 LOGOUT 19 BM 20 DET 21 SUPDUP 22 SUPDUPOUTPUT 23 SNDLOC 24 TTYPE 25 EOR 26 TUID 27 OUTMRK 28 TTYLOC 29 3270REGIME 30 X3PAD 31 NAWS 32 TSPEED 33 LFLOW 34 LINEMODE 35 XDISPLOC 36 OLD_ENVIRON 37 AUTH 38 ENCRYPT 39 NEW_ENVIRON 40 TN3270E 41 XAUTH 42 CHARSET 43 RSP 44 CPCO 45 TSLO 46 STARTTLS 47 KERMIT 48 SEND-URL 49 FORWARD_X 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 MSLP 69 MSDP 70 MSSP 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 MCCP1 86 MCCP2 87 MCCP3 88 89 90 MSP 91 MXP 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 PRAGMA LOGON 139 SSPI LOGON 140 PRAGMA HEARTBEAT 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 ATCP 201 GMCP 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255

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