Remove the configuration prompt

I should probably write this one on April 1st, but maybe October 31st is not such a bad choice after all … if you configure no service prompt config, the configuration prompt is gone; when you enter the configuration mode with the configure terminal command, you get an empty line (like you did with Cisco software release 9.1 some 15 years ago). Similarly, you can disable command-line editing with the no editing line configuration command or terminal no editing exec-level command. If only there would be a way to disable the context-sensitive help :)

9 comments:

  1. Yeah... IOS 9.1 :D
    Ivan, I've a question:
    What was your first Cisco device(s) to manage?
    Mine was Cisco 3000 & 7000. I started to late to put hands on AGS+.

    ReplyDelete
  2. I started with an IGS-derived blade for a Cabletron modular hub running 8.3. We had a lot of IGS and AGS+-es in production networks, with occasional MGS thrown in. The only one I've luckily never worked with was the CGS.

    BTW, there's still MGS/CGS hardware documentation on CCO.

    ReplyDelete
  3. Ivan Pepelnjak wrote...
    > The only one I've luckily never worked with was the CGS.

    Why luckily? What was wrong with CGS?

    BTW: the MGS/CGS hardware documentation has one funny statement:
    "[...] and T refers to high- speed (T1) serial lines (up to 4 kilobits per second [kbps])."

    Did you know how poor T1 was implemented these days? :D

    ReplyDelete
  4. AGS+ was newer, there was AGS (w/o the +). Then there was CGS, MGS, and IGS. Remember the old CS-500 and ASM? Were they the good old days? Nay, I hated burning eproms and playing with ribbon cables. Not to mention that when u needed to add serial ports to the AGS, you have to unassemble the entire AGS in order to get to it.

    And then there were jumpers and dip switches on the circuit boards.

    BTW, the IOS (not even called IOS back then) back then was actually burned into EPROMs, not flash memory. Talk about IOS upgrade...you can have your coffee break numerous times while watching the neon light glowing in the eprom eraser.

    ReplyDelete
  5. From these days I also remember hardware config-register (a big set of jumpers) which disappear when RP and SP was merged to form a single RSP card in 7000. IOS was named Gateway Software or something like that.

    ReplyDelete
  6. I've never seen an AGS, but if I remember correctly from the RHC (Router Hardware Configuration) class, it was the same chassis as the AGS+.

    Change-wise AGS+ was the easiest one, at least the panels were on the front and the back. To remove a board from a rack-mounted MGS, you had to remove the MGS from the rack or remove the side wall of the rack.

    CGS was a royal pain, to change an applique you had to tear it apart completely. Our instructor in the RSC (Router Software Configuration :) class tried to demonstrate it and gave up after 10 minutes.

    And for those of you that are too young to know what an applique is: in the good old days, the Multibus boards had TTL-level (no, that's not time-to-live, it effectively means 5 volts) serial signals that were transported via a ribbon cable to a small PCB with interface chips on which the actual connector was mounted. If you wanted to change from RS-232 to X.21 (for example), you had to change the applique. No wonder the current serial cables were seen as a gift from heaven.

    Of course, the gateway (the "proper" name for a layer 3 switch :) software was running from EPROMs. We actually had a few networks under maintenance contract where we had to go out and change the chips every now and then. And there was no way a hacker (or a joker) would mess up your config register (changing the console baud rate, for example)without opening the box and moving the jumpers ;)

    ReplyDelete
  7. Getting back to the original post, there are all kinds of weird things that can be done with the prompt in IOS.

    For example you can add control characters to the hostname by using the control-v method of entering control characters. So add to a bell to the end of the hostname you can do: Router(config)#hostname myhost^v^g
    Now you get a bell every time the prompt is displayed - an annoying April Fools trick that I try to use every year on lab routers.

    In the "slightly more useful" category there is a prompt config command so you can change the exec prompt to be different from the hostname or to contain more information than just the hostname. For example: Router(config)#prompt %h/TTY%n%p

    And the last weird command that would be good on April 1st that I can think of is: Router(config)# prompt config hostname-length 0

    ReplyDelete
  8. Oh one more thing, using no service prompt config will trip up EEM policies (applets and Tcl policies) that use the cli actions or the Tcl cli library to go into config mode. The only way around this would be to use a Tcl policy that uses cli_write to go into config mode and write all of the config commands out without trying to read the prompt until the last config command is entered and followed by the "end" command.

    ReplyDelete
  9. what a bunch of geeks! :)

    ReplyDelete

You don't have to log in to post a comment, but please do provide your real name/URL. Anonymous comments might get deleted.

Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.