From: jonatale@xxxxxxxxxxxxx
Date: Sun Sep 09 2001 - 03:14:54 GMT-3
The shftt-cntrl-6 = <ctlr,^> = 0x1E = 30 = ASCII Record Separator character
(note that the crtl key basically subtracts 64 from the [upper case version] of
the char but could be keyboard type dependent) is the default escape char on a
cisco. The esc char tells the communication device that the next char will
represent a command for itself, so the communication device will not pass
either char. The list of commands (vendor dependent), *I think*, is given by
"shftt-cntrl-6, ?" - this was in an email on this list about 4 weeks ago. Just
like in Bisync and in SLIP, if the escape char needs to be sent thru then two
esc chars are sent. This is why if you daisy chain ciscos together (term to con
of first, aux of first to con of second, aux of second to con of third, etc.)
and reverse telnet to each one sequentially then you must enter "<ctlr,^>,x" to
get back to the the first cisco, "<ctlr,^>,<ctlr,^>,x" to get back to the
second cisco, "<ctlr,^>,<ctlr,^>,<ctlr,^>,<ctlr,^>,x" to get back to the third
cisco,
"<ctlr,^>,<ctlr,^>,<ctlr,^>,<ctlr,^><ctlr,^>,<ctlr,^>,<ctlr,^>,<ctlr,^>,x" to
get back to the forth cisco, etc.
The escape SEQUENCE is the command that tells the communication device to
terminate the character stream locally rather than passing the character stream
thru, on a cisco it is represented by "<ctlr,^>, x".
The break SEQUENCE is the command that tells the communication device to send a
break SIGNAL instead of passing the character stream thru, on a cisco it is
represented by "<ctlr,^>, b".
The break SIGNAL is a momentary raising of the voltage to +. It is not an ASCII
character. It is similar to toggling DTE, but many terminal use only 3 pins
(TX, RX, GND) so this is a way to send a [very (OSI layer 1] low level signal.
When the cisco receives a break signal while it is booting, it stops booting
and falls back to ROMMON mode, which is a limited OS typically contained in
hardware (on a chip). The reason it is in hardware is because hardware is less
likely to get corrupted so if the software gets corrupted the box can usually
at least get to the ROMMON where the software can be fixed.
The config-register can be set such that when the cisco receives a break signal
AT ANY TIME, it falls back to ROMMON mode.
There is no way, to my knowledge, to force the cisco to fall back to ROMMON
mode at any time via telnet. This is probably for security reasons.
In conclusion, maybe if:
set config register such that it will always fall back to ROMMON mode when
receives a break signal
(obviously, must already be booted to telnet in)
connect aux to con
telnet to port 2001
then you can get to ROMMON via telnet (my guesses are are that your session
will drop because ROMMON does not support telnet server)
PS
There is a telnet break - but how to send it depend on your telnet client, and
what it does - I don't know. I know cisco does have a command(s) dealing with
this.
config reg
Ademola Osindero wrote:
> Connect from the console.
>
> --- David Morton
> <David.Morton@OpenTelecommunications.com> wrote:
> > I hate to admit that I'm stumped on this one too.
> > I'm connecting to my
> > routers via Win2K telnet to a 2509 acting as a
> > terminal server.
> >
> > I've tried all the key combinations in the link
> > below, but have no luck.
> > Some combos do cause the ############ to shift to a
> > new line, but the IOS
> > load continues.
> >
> > If I directly connect via a console cable, it works
> > flawlessly. Obviously
> > I'm missing something simple, so be kind :>
> >
> > Take care
> >
> > David
> >
> > David Morton CCNP, CCDP
> > Principal Engineer
> > O p e n T e l e c o m m u n i c a t i o n s
> > davidm@ot-usa.com
> >
> >
> > -----Original Message-----
> > From: Peter Farkas [mailto:pfarkas@cisco.com]
> > Sent: Thursday, September 06, 2001 1:43 AM
> > To: Alex Hsieh
> > Cc: ccielab@groupstudy.com
> > Subject: Re: dumb question
> >
> >
> > Here is the page on cco about it:
> >
> > http://www.cisco.com/warp/public/701/61.html
> >
> >
> > Alex Hsieh wrote:
> > >
> > > hi group
> > >
> > > I know this is a silly question,please be
> > patient with me.Can anyone
> > > please tell me what "break sequence" means when
> > you want to change config
> > > register?Thanks for help.
> > >
> > >
> >
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