From: Jay Hennigan (jay@xxxxxxxx)
Date: Tue Jan 16 2001 - 16:29:14 GMT-3
On Tue, 16 Jan 2001, Mohammed Misba wrote:
> Hi all,
>
> This commond is use to reduce noise on console line , if there is much
> noise, a bunch of garbage will show up on the screen, to resolve this
> problem use this commind.
> line [begin line #] [last line #]
>
> no exec
I wouldn't try that on a console line, unless you have another way into that
router.
What it is for, in the case of a terminal server, is to prevent noise or
bootup messages from the connected devices on the async lines from being
interpreted as commands by the terminal server itself. Otherwise, you have
two command-interpreting lines back-to-back, and they'll just jabber error
messages at each other, as each side tries to parse the other side's boot
message, console logs, etc. as if it were a command. So, on aux or async
lines that aren't being used for configuring the router, it's a good idea.
See:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/fun_r/fr
prt1/frconban.htm#xtocid2971041
-- begin excerpt ---
Usage Guidelines
This command first appeared in Cisco IOS Release 10.0.
When you want to allow an outgoing connection only for a line, use the
no exec command. When a user tries to Telnet to a line with the no exec
command configured, the user will get no response when pressing the Return
key at the login screen.
Example
The following example turns off the EXEC on line 7. You might want to
do this on the auxiliary port if the attached device (for example, the
control port of a rack of modems) sends unsolicited data. If this happens,
an EXEC process starts, which makes the line unavailable.
line 7
no exec
-- end excerpt --
So, doing this on your console port would, in most circumstances, be a
very bad idea. It won't kick you from your present session, but once you
exit, you won't get back in.
Recovery from this situation is similar to password recovery. I've tested
this in the lab, both accidentally [1] and intentionally.
[1] Hint: Don't abbreviate "no exec-timeout" as "no exec".
-- Jay Hennigan - Network Administration - jay@west.net NetLojix Communications, Inc. NASDAQ: NETX - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323
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