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000346_news@columbia.edu _Sat Jun 3 14:08:43 2000.msg
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From: fdc@columbia.edu (Frank da Cruz)
Subject: Re: Login garbage
Date: 3 Jun 2000 17:50:27 GMT
Organization: Columbia University
Message-ID: <8hbgh3$5le$1@newsmaster.cc.columbia.edu>
To: kermit.misc@columbia.edu
In article <sjg664v25ri77@corp.supernews.com>,
Alan Rice <alanrice@bigfoot.com> wrote:
: Hello Guy's I'm having a simple problem that's been giving me fits.
: Some times when a client machine calls into our unix host I get false
: positive login's.
:
: What is happening is that the modem seems to get trashed out. instead of
: answering with a clean <login: >. It will answer with trash like <RING's
: Passwd: >.
:
: I thought I wrote the login script below right to handle this but it's not
: working.
: I think it's seeing the portion for the login input it's looking for in the
: input buffer as < login: RING> and going forward to the password portion.
: Now RING is not the only garbage I've seen, There has been CONNECT , LC1,
: LC2, ect. I wanted it to look for <login: >.
:
: What am I overlooking? In the Using C-Kermit 2nd Edition on Pg 436, the unix
: login script is incomplete.
:
Right -- it's a mistake, documented in the update notes:
http://www.columbia.edu/kermit/ckermit2.html#xiv
The "input xxx Password" sequence is missing. However, the copies of these
macros that are delivered with C-Kermit (in the ckermit.ini file) are correct:
ftp://kermit.columbia.edu/kermit/f/ckermit.ini
The RING, CONNECT, and other sequences you are seeing are result codes from
your modem, which are used by software such as Kermit when dialing out.
When a modem is used for receiving calls, however, it should be configured
not to display result codes because if it does, as you can see, this
confuses the heck out of getty. Example: Call comes in, modem turns on RI
signal and prints RING; getty turns on DTR, sees RI and spawns login, which
issues the "login:" prompt. Login sees "RING" as somebody trying to login
under the username RING and prints the Password: prompt. Meanwhile the
modem has echoed the "login:" prompt back at the computer, which it reads
as the password, which normally fails, so it issues another login prompt.
Well, by this time the modem has issued its CONNECT report, and the computer
reads this as a response to its second login prompt, etc etc. This is
known in the trade as "getty babble".
To avoid getty babble, the answering modem must be configured as follows
(the commands shown are for USR modems but should be fairly portable):
&C1 CD up only when connected to another modem.
&D2 Modem hangs up if computer drops DTR.
E0F1 Don't echo.
S0=1 Answer the phone after 1 ring (Answer mode).
Q2 Suppress result codes in answer mode (or Q1, always suppress them).
S2=128 Disable "+++" escape.
The tricky part is to set up your answering modem so these commands are
always in effect; the method varies from modem to modem. Example for USR:
AT&C1&D2E0F1S0=1Q2S2=128
AT&W
The last command means "write the current configuration to NVRAM to serve
as the reset default".
- Frank