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CS-328

CS-328. Rlogin & Telnet Protocols. Rlogin . Remote Logon to another Host RFC 1282 Well known port : 513 . Rlogin Method. Client sends 4 null terminated strings to server byte of 0s logon name of user on client; byte of 0s logon name of user on server; byte of 0s

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CS-328

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  1. CS-328 Rlogin & Telnet Protocols

  2. Rlogin • Remote Logon to another Host • RFC 1282 • Well known port : 513

  3. Rlogin Method • Client sends 4 null terminated strings to server • byte of 0s • logon name of user on client; byte of 0s • logon name of user on server; byte of 0s • user’s term type ‘/’ term speed; byte of 0s • Server responds by sending a byte of 0s

  4. Rlogin Method (cont) • Server can optionally ask for a password • handled as normal data exchange, no special protocol • passwords are sent as clear text; newer versions use Kerberos • Server usually requests client to send terminals window size

  5. Client responsibilities • send a byte at a time to server; echoing is done by server • text compression and decompression; Nagle’s algorithm

  6. Client commands • Flow Control • Control-S ,Control-Q • sent using TCP Urgent • “Raw” mode • Start Stop are sent to server as any other data; server determines the semantics and either uses for flow control or passes to local app (ex EMACS)

  7. Client Commands (cont) • “Cooked” mode • Start/Stop are interpreted at client to start and stop server from sending more data • May lose many characters before server may implement Stop • Control Commands (sent by server) • TCP Urgent • 02 - client discards all buffered data • 10 - enter “raw” mode • 20 - enter “cooked” mode • 80 - window size request

  8. Telnet • Remote logon to another host • RFCs 854 and 855 • Well known port: 23

  9. Network Virtual Terminal (NVT) • Both Telnet end points implement NVT • can’t rely on option negotiation as one end might be a hardwired terminal (like a TTY) • bi-directional character based device • conceptionally consists of a • keyboard • printer • unspecified line length and page length

  10. NVTs • understands ASCII printable codes (32-126) and NULL, LF, CR • BELL (7), BS (8), HT(9), VT (11) FF(12) are optional • embedded in line with the above chars are telnet commands

  11. Telnet Commands • commands are placed in the data stream by first inserting an IAC (Interpret as command) character (255) • Commands are of the form: • IAC verb option • to have NVT not interpret 255 as IAC, use two consecutive IACs

  12. Telnet Commands • SE-240 - end of subneg.parameters • NOP-241-No Operation • DataMark-241-accompanies TCP Urgent • Break-243-Break or Attn Key • Interrupt Process-244-Suspend,terminate remote process

  13. Telnet Commands (more) • Abort Output-245-complete remote process without output • AreYouThere-246-rqst remote NVT ot give some sign of life • EraseChar-247-tell remote NVY to erase last char • EraseLine-248-tell remote NVT to delete last line

  14. Telnet Commands (more) • GoAhead-249-Go Ahead signal • SB-250-subnegotiation begin • WILL-251-desire to begin performing • WONT-252-refusal to perform • DO-253-reqst other party perform • DONT-254-demand remote stop • IAC-255-Interpret As Command

  15. Option Negotiation Commands • Will-offer to remote to perform • Do-remote agrees • Don’t-remote disagrees to offer • Won’t-offer to remote to not perform • Do-remote disagrees to the offer • Don’t-remote agree to offer

  16. Option Negotiation Commands • Do - request remote to perform • Will- remote agrees to request • Won’t-remote disagrees to request • Don’t-request remote to not perform • Will-remote disagrees to request • Won’t remote agrees to request

  17. Standard Options 0- Binary Transmission 1 - Echo 2 - Reconnection 3 - Supress GA 4- Approx Msg Size 5 - Status 6 - Timing Mark 7 - Rem.Control Trans & Echo 8 - Outout Line Width 9 - Output Line Size 10 - Output CR Disposition 11 - Output Horiz Tab Stops 12 - Output Horiz Tab Disposition 13 - Output FormFeed Disposition 14 - Output Vertical Tabstops 15 - Output Vert Tab Disposition 16 - Output Linefeed Disposition 17 - Extended ASCII 18 - Logout 19 - Byte Macro 20 - Data Entry Terminal 21 - SUPDUP 22 - SUPDUP Output 23 - Send Location 24 - Terminaltype 25 - End of Record 26 - TACACS User Id 27 - Output Marking 28 - Terminal Location Number 29 - Telnet3270 30 - X.3PAD

  18. Suboption Negotiation • Some options can’t be negotiated by simple option negotiation... • IAC SB option parameters IAC SE

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