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Text File | 1992-11-17 | 20.6 KB | 407 lines

The WATTCP TELNET Server by Erick Engelke This program allows you to remotely control your pc. It is a pretty simple implementation, but usable enough for many people. For a much nicer but commercial TELNETD implementation (colour, kermit file transfer, remote printing, multinational characters, 24 or 25 lines, etc.) contact info@snsi.com about Everywhere Access. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- WARNING - TELNETD offers some simple password security provisions but remember: 1. TELNETD gets the password from an unencrypted disk file 2. TELNETD stores the password in memory as plain-text 3. All TELNET protocols send the password over the network in plaintext - it's trivial to read a password on networks such as Ethernet. The password protection is merely one step above no protection. Do not leave important information accessible through TELNETD. Change your password frequently and use mixed case and numbers interspersed. Avoid single words, use combinations of words. Do not use the same password for TELNETD as you would for your system priviledged account. The maximum password length is 16 letters. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Installation TELNETD.EXE uses the Waterloo TCP kernal to do all the network i/o. Installing the program can be performed by simply editing the ASCII configuration file named WATTCP.CFG. Try creating such a file with information like the following and place it in the *SAME* subdirectory as TELNETD.EXE. ---I:\NETWORK\WATTCP.CFG---------------------------------------------- my_ip=129.97.128.254 # substitute the PC's ip number netmask=255.255.254.0 # substitute your local net mask gateway=129.97.128.1 # substitute your local gateway # the next lines are optional telnetd.password=Time2Go # telnetd session password telnetd.message="Wizbang Computer Network" # openning message ---------------------------------------------------------------------- You need not include quotes except if you wish to include non-alphanumeric characters like '#',';' or spaces. Full installation instructions for installing any Waterloo TCP based program is available from sunee.uwaterloo.ca [129.97.128.196] in pub/wattcp/apps.zip. If you end up having difficulty running TELNETD, download that zip file, it will prove very useful. Also included in that file is information on how to use BOOTP, multiple gateways, and many other features. The above type of configuration is useful in all WATTCP based programs, but you can also add some special parameters which will only be interpretted by specific WATTCP programs. In this case all parameters specific to TELNETD are prepended with 'telnetd.' to make them easily identifiable and to avoid naming conflicts with other WATTCP applications. Load (and configure) an Ethernet packet driver, then run TELNETD. A message will appear indicating TELNETD is waiting for a caller and it should report the correct IP address. An indication of a password should appear for every time it encounterred a password in the configuration process. If no packet driver is installed TELNETD will have crashed by now. Installing TELNETD on a Network Do everything the same as above, but append the following line to the WATTCP.CFG file: include=?c:\telnetd.pas and have user's place their private password in that file. Eg. ---C:\TELNETD.PAS----------------------------------------------------- # joe's private config parameters telnetd.message="Joe's Private Computer - KEEP OUT ALL SURF NAZIS" telnetd.password=Knuths4thBook ---------------------------------------------------------------------- In the above example I assumed the 'c' disk was the local hard disk. You could select the network disk or both. Here the network disk n: has the last say on the password. The telnetd.password directive can appear several times and in several files, but the last occurance is the password actually used. include=?c:\telnetd.pas include=?n:\telnetd.pas The question mark tells TELNETD to use the file if it exists but not complain if it doesn't. You may like to leave a default password in the WATTCP.CFG file, just so intruders are less likely to break in. There are some other parameters which are sometimes good to set. One which can enhance security is the inactivity timeout. Setting this value to a non-zero value tells WATTCP to hang up the connection if no activity occurs for a certain period of time. A good value would be something like twenty minutes. Smaller values can be -- WATTCP.CFG -------------------------------------------------------- # assuming properly configured as described earlier # print a message for local user print="Press control-break to get out of this thing" # set the inactivity timeout value inactive=1200 # 20 minutes ( 20 min x 60 sec/min = 1200 seconds ) ---------------------------------------------------------------------- Using TELNETD Go to a second PC. Using Clarkson University (CUTCP) TELNET, telnet to the first PC. You could use NOS (KA9Q), but I don't think NOS handles VT100 cursor keys and you will definately want them! Other tested telnets include MicroVaxen, RS/6000 using AIX and Macintoshes using MACTCP When you TELNET to TELNETD, you may have to hit return. It's one of those things left to fix. Sorry, but it's getting too late tonight. You will then be confronted with a login message (from the wattcp.cfg file) and a password prompt (if you selected a password in the configuration file - otherwise skip this paragraph). You must enter the password correctly within a reasonable number of tries or TELNETD will complain and close the session. You must also reply within a reasonable time limit. The passwords can be almost any printable ascii string up to 16 letters. If you use characters other than alpha-numerics, you should surround the password with quotes in the WATTCP.CFG file. WATTCP removes the quotes when it parses the file, so you don't enter the quotes when you enter the password at the prompt. Assuming you passed the password test, TELNETD becomes a TSR and almost immediately you will be at the DOS prompt. You are now logged in. Anything you type on the remote PC will appear to be typed on the TELNETD PC. QEDIT, LIST.COM, BORLAND C++, and many other programs are compatible (check out the character translation). There will be slight periodic delays. Using a 386 to run TELNETD will improve your performance. If the screen appears to be messed up or incomplete, you can have TELNETD redraw it by typing ESC R on the keyboard. This usually happens from either a lost packet or contention on the network card if you are using the same card for network disk i/o. For example, if I am compiling then TELNETD can find very few cracks in the network i/o because my computer is diskless. But most operations are not so incredibly disk intensive and it feels quite reasonable. Remember that the remote PC is running VT 100 emulation and some keystrokes have to be remapped. I have written support for VT100 and VT220 terminals, but not everything has been tested yet. a-z, A-Z, 0-9 function normally. cursor arrows function normally To enter CONTROL-CHARACTER, eg. ^A, press ESC C A To enter ALT-CHARACTER, eg. ALT A, press ESC A A To enter SHIFT-Something eg. SHFT <- press ESC S <- To enter function keys eg. F9 press ESC F 9 To enter ESCape press ESC E ** To exit (logoff and reboot) press ESC X ** To redraw the screen (clean up mess) press ESC R ** To get online help press ESC H, the next keypress removes the help screen. There are some extra VT100 and VT220 keystrokes available. The VT220 user can usually use both VT100 and VT220 keystrokes. PC VT100 VT220 ESC H HELP get online help ESC ESC E F11 BCKSPC BS F12 vt100 not confirmed INS Insert DEL Remove END pf4 DOWN down arrow down arrow PgDn Next Screen LEFT left arrow left arrow 5 Select RIGHT right arrow right arrow HOME pf3 UP up arrow up arrow PgUp Prev Screen F1 ESC F 1 1 on numeric keypad ... ... F9 ESC F 9 9 on numeric keypad F10 ESC F 0 0 on numeric keypad F11 pf1 F12 pf2 Notes on Using TELNETD When you don't know how to do something, try the online help (ESC H). Many other keystrokes are built out of combinations, for example, Shift F7 is attained by typing 'ESC S ESC F 7'. Sorry, but that's the way it is right now. Kermit users may wish to write a kermit script to remap the keyboard and provide really nice emulation. If you do it, please send me a copy too. Once connected, TELNETD does some neat things. It automatically compensates for slow data lines. Here's how I call in from home: PC <-- 10 Mbps <-- PCRoute <-- Ethernet <-- Telnet <-- Modem <-- phone <-- home Token Ring Server PC \______________________________________________/ \__________________/ high speed media 1200 baud TELNETD attempts to use your network card during the timer tick. The packet driver or network card may be in use and report a transmission error. No problem, TELNETD will retry a little later and eventually get through, but that explains the bumpiness you may notice during network disk operations. If you've had a high count of network errors, the tcp/ip portion of TELNETD will take a couple of packets to recompute the correct response time. Enterring a few keystrokes or using ESC R to redraw the screen will generate the necessary traffic to restablize the the round trip time. Although very rare, you may notice a little garbage on the screen. This is usually something to do with ANSI escape sequences. The quick solution is to redraw the screen with ESC R. If you see these with any frequency, please let me know. When you wish to end your TELNETD session, either have your local TELNET program close the session or use 'ESC X' which will tell TELNETD to close the session. Simply rebooting the TELNETD machine or the TELNET machine is bad since the other machine will keep trying to communicate and will annoy your network manager. Limitations: I *DID* mention that this is not perfected. Here are the current problems that come to mind: 1. screen updates are sporatic - hey, don't be picky - but they are getting much better 2. You cannot run other TCP/IP programs. This is a limitation of the packet driver combined with the fact that no other programs use TELNETD as their TCP/IP kernel. 3. VT100's don't have a way to do *all* the cursor keys, well I just haven't come up with keystrokes for all of them. If you have some good ideas, send me a list. 4. TELNETD may show update delays because of network card contention. Basically, if you are using your network card for something like NOVELL file service, TELNETD won't know that and will attempt to use the card at the same time which may cause delays. My computer is diskless too, but it doesn't feel that bad. 5. Screen blankers may cause problems and should not be installed. I find this to be a general truth though I know everyone has found one which works with (almost) every other program. Notes: 1. When you logoff or reset your connection or it timesout from inactivity (if past the password prompt) I reboot the machine. This way your autoexec can set it up for the next call and sensitive network accounts can be managed more gracefull. 2. TELNETD automatically adjusts itself to work efficiently with low performance and low bandwidth networks. How Does It Work? TELNETD passively watches the local screen and actively changes the keyboard buffer. In essence, it performs whatever is necessary to share the computer with a remote session, and attempts to consume as little processor time as possible doing so. TELNETD chains into the timer tick, meaning it gets a little bit of processing time every time the computer's clock ticks. That works out to about 18 times per second. It is pretty careful with precious computer time, so it never sits in any form of idle loop. You should not experience a significant processor slow down while running TELNETD unless you are working on an 8088. During that time slice TELNETD checks to see how much data the remote computer has accepted from previous screen updates. If there is still lots of unaccepted data, the remote computer is probably relatively far away and TELNETD doesn't bother sending updates as often. This results in jerkier screen updates, but it reduces the load on the intermediate networks. If the last update is largely complete, TELNET completes the following steps to do the next update. The update process works by comparing the screen memory against a local buffer. Differences are locallized to a particular screen line and the first and last changed character on that line. Eg. line 12, characters 23 to 36. The data is massaged, turning PC graphic characters into ASCII characters and converting long sequences of spaces into faster escape codes such as clear-to-end-of-line. Typically an escape sequence is sent saying, goto line 12, character 23, and then 13 ASCII characters are then transmitted. Special optimizations are made to try to reduce the number of lines sent by checking for scrolled screens. If the screen appears scrolled, TELNETD sends commands to scroll the remote screen. TELNETD transmits chuncks of information until a certain number of lines appear in transit, currently that value is 12 lines, or up to approximately one kilobyte. Then the remote cursor is positioned at the correct screen location. In all its screen updates, TELNETD must constantly deal with the fact that the remote computer can only display 24 lines as compared to the 25 lines on the local screen. It attempts to handle this by only looking at the 24 lines containing the cursor, ie. if the cursor is on the upper-half of the screen, TELNETD shows the first 24 lines, otherwise the last 24 lines. Again, it uses the VT100 scrolling sequences to toggle between the two efficiently. TELNETD relies on the fact users get confused by frequent screen updates, thus most applications do not change a significant portion of the screen very frequently. The common exception is editors and word processors which tend to update the current line and status lines with every key pressed. TELNETD must also read characters from the network. It builds them into a string in local memory and compares that string agains known keystrokes. If a match could exist, ie. you typed ESC A but not the third letter, TELNETD does not do anything with the data until the next letter is received. When a simple keystroke arrives, or a complex keystroke (eg. ALT A) is completed, TELNETD must find the PC scan code equivalent. It does this by searching a table. Finally, the ASCII/ScanCode value is placed into the BIOS keystroke table in low memory and the BIOS thinks the PC enterred the keystroke. TELNETD must also deal with passwords and the possibility that the remote person wishes to use its internal help or logoff facilities. These are managed from the keyboard dispatch section just like other keystrokes. Future Enhancements TELNETD and the underlying kernel were all written by me. You can guess I've been pretty busy. I tried to design the kernel so oddball applications like TELNETD could be written in 'C' and without looking like some of the nastier UNIX or Bible sequences. The number of TELNETD users is growing and I think the program has become pretty reliable. I really appreciate mail from users, I've put a good deal of rainy day time into this project and it feels good to know that others can benefit from the effort. There are some items which are still untidy, like the first password attempt mess. That's the problem when a person has a real job and only writes software like this on rainy weekends. I'll eventually get around to it, just pray for bad weather. I live in Canada so you don't have to pray that hard. I post news to comp.protocols.tcp-ip.ibmpc when major improvements are made to TELNETD or I am releasing other free software. In case you are interested in TCP applications programming, you may like to look at some of the other applications available. FTP to sunee.uwaterloo.ca [129.97.128.196] and get pub/wattcp/src.zip Suggested Uses for TELNETD Here are just some of the practical uses for TELNETD. 1. People who are away from their desks can quickly call in to check files, mail, etc. Some prime candidates are when you are in a meeting and you need something from your computer, any terminal, mac or pc will allow you access if it is somehow connected to the Internet. 2. If you have a Dial up TELNET server, you can allow people to call in from home (much like PC Anywhere), but without requiring modems in their office PCs. 3. Consulting can be simplified. Set up an easy to use batch file which invokes TELNETD. When someone calls your consultant they will be able to talk over the phone and use TELNET/TELNETD to solve the problem. If you have MARK/RELEASE you can remove TELNETD from memory without rebooting. 4. Some applications (such as databases) need to be accessible to people at remote locations or on different computer systems. TELNETD lets you to network existing applications on the PC rather than programming on multiple platforms or trying to get databases to work over wider area networks. Good luck, and I hope TELNETD fulfils some of your needs in a remote computing facility. Erick Engelke Waterloo TCP Architect erick@development.watstar.uwaterloo.ca =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-