Connecting Modem to Console on 1700 series
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Posted by scotty.west@gmail.com on May 17, 2006, 10:55 am
Please log in for more thread options I currently have a cisco 1700 that I'm trying to connect a modem through to the console port. The modem answers and says connected (see below from my management station) tip nops connected attd 901322359XXX CONNECT 19200/ARQ/V34/LAPM/V42BIS But moves no further from this prompt Heres a copy of the configuration of the console port on my router: line con 0 exec-timeout 120 0 password 7 xxxxxx login authentication console Does anyone have any suggestions on succesful ways of configuring this? If I connect the the AUX port it works fine. Cheers S | ||||||||||||||||
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Posted by GusttyWinds on May 17, 2006, 11:21 am
Please log in for more thread options understanding is that you must use the auxillary port. | ||||||||||||||||
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Posted by J on May 17, 2006, 11:39 am
Please log in for more thread options Try knocking your modem down to 9600 baud and the other settings of
8N1. J | ||||||||||||||||
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Posted by Aaron Leonard on May 25, 2006, 5:06 pm
Please log in for more thread options wrote:
~ Hi Guys ~ ~ I currently have a cisco 1700 that I'm trying to connect a modem ~ through to the console port. ~ ~ The modem answers and says connected (see below from my management ~ station) ~ ~ tip nops ~ connected ~ attd 901322359XXX ~ CONNECT 19200/ARQ/V34/LAPM/V42BIS ~ ~ But moves no further from this prompt ~ ~ Heres a copy of the configuration of the console port on my router: ~ ~ line con 0 ~ exec-timeout 120 0 ~ password 7 xxxxxx ~ login authentication console ~ ~ Does anyone have any suggestions on succesful ways of configuring this? ~ If I connect the the AUX port it works fine. ~ ~ Cheers ~ S The problem is likely that the answer modem has decided to set its DTE rate to 19200 bps while the console port is set to 9600 bps. Following is some hard earned advice on connecting modems to console ports. Issue #3 is likely yours. Cheers, Aaron --- When you configure a modem on the console, you need to be aware of a few things: 1. The modem port does not do modem control. This is a problem for a couple of reasons: 1.1. If the call should hang up, the line will not drop. So this is a possible security threat - one user could log in then the modem connection could drop, then someone else could dial in and be at the console port without having had to authenticate. Workarounds: use a modem with a built-in password; configure a short exec-timeout to shrink the window of vulnerbility. 1.2. On a line with modem control enabled (modem inout or modem dialin), the line will be up only if we see DSR - i.e. if DCD (modem carrier) is high. The modem will normally output result codes such as "NO CARRIER", "RING", "CONNECT 9600" etc. only while its DCD is low - therefore, modem result codes will not be seen by the line as user input (unless you've configured 'no flush-at-activation'.) However, a line with no modem control (such as the console) sees ALL characters received as user input. This is probably what causes the problem described below ... the modem has output result codes, and IOS is seeing this as input to the Password: prompt. Sometimes the modem's AT parser can get into a "babble loop" with the console parser, where each device is continuously outputting error messages in response to the other's error messages. Therefore, a modem on the console should always be configured for "dumb" mode - do not display result codes and do not echo commands, do not even parse AT commands. 2. Since you have to configure the console modem not to display result codes, this means that modem autoconfigure can't work (not sure if it could work in any case on a console line.) Therefore in order to configure the modem as desired, you must enter the config via the AT interface and store it in modem NVRAM (&W typically.) 3. Most modems unfortunately are unable to be explicitly configured to a fixed DTE rate, and instead infer the DTE rate via autobauding to characters received on the AT interface. With such modems (especially USRs), if you have only incoming not outgoing calls (as would be the case with a console port) and if the DTE doesn't periodically send AT commands (as would be the case without modem autoconfigure), the modems are apt to forget what DTE rate they're supposed to use, with the result being that you call in and the modem decides that its DTE rate should be 38400 bps or some dumb thing and so it can't talk with the console which is 9600 bps. Workaround: configure the modem for a fixed DCE rate of 9600 bps (with EC but no compression), and configure its DTE rate to follow the DCE rate. To summarize how to configure a modem on the console port then: - force the modem to connect at a 9600 bps modulation (DCE link speed) - either lock the DTE port speed at 9600, or else have the DTE speed track the DCE speed (which is locked at 9600) - enable error control - no flow control - DTR forced high - autoanswer - do not transmit result codes - do not echo AT commands - do not parse AT commands at all (dumb mode) You can configure the modem by using DIP switches and/or AT commands. To send the modem AT commands: connect to it via reverse telnet out an aux port, or from a terminal program on a PC COM port. Issue the AT command string ending with &W to write the configuration to NVRAM. Note that you had better know what you're doing, since the AT interface will be disabled after you issue the command. --- Here are the steps to take specifically with a USR Courier Modem to connect to a cisco router console port. 1.) Hook up modem to COM port on PC 2.) Set Hyperterminal settings to: 9600 bps 8 databits no parity 1 stopbit no flow control 3.) connect to modem and issue the following AT string: at&f0s0=1&b0&n6&u6&m4&k0&w &F0 - no flow control factory template S0=1 - autoanswer after 1 ring &B0 - serial port rate follows DCE rate &N6 - 9600 bps max DCE rate &U6 - 9600 bps min DCE rate &M4 - EC with fallback to async &K0 - no data compression &W - write to NVRAM 4.) set dip switches on modem to 1-3 up...4 down...5-10 up 5.) power-cycle the modem 6.) set configuration on console port of router to: line con 0 exec-timeout x y --> where "x" is minutes and "y" is seconds
login
password xxxxx --> where "xxxxx" is your exec password
...and that's IT!!
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