Connect external modem to 3024 console port

Question

Since these switches have a tendency to lock up despite my best efforts and every suggestion on this forum, (though curiously I have never had the console lock up) I would like to connect an external modem to the switch's console port so that I can reboot the switches when I cannot contact them in-band. So far I have had no luck getting this to work beyond the external modem answering and handshaking with my laptop modem. Does anyone here have any init strings/suggestions/advice? I'm using a USRobotics Sportster 33.6 external, specifically it is model 000839-09. Also, should I be using a standard modem serial cable between the modem and the console port on the switch, or a null-modem cable (which sounds counter-intuitive, but which I am willing to try since nothing else seems to work). Also, the modems are known to be good, I used to use them for remote management of some SCO Unix boxes. Thanks in advance.

Bryan

galland101 · Answer

I don't think the console ports were meant to work that way.  The simplest thing to do would be to hook up the console port to a PC with terminal emulation software, then use remotely access that PC using a VPN and VNC, then run Hyperterminal from there.  Hopefully that switch doesn't take down your whole network when it freezes.

braybk · Answer

Oh, I assure you, that's how it's supposed to work.  I can connect to serial console ports on my Cisco, HP, and Enterasys switches with modems, but for some reason I can't with these.  I don't think it's a switch problem though, I really think it's in the modem settings, but for some reason the same settings that work with other devices just won't work with these switches.  And yes, the reason I'd like to do this is because when the switches go down, the whole network goes with them.  Strangely though, the console is always still working even though the switch won't pass traffic.

mstavale · Answer

I was able to use a USR V.Everything modem to console to my 6024f router so that should work for the rest of the dell family.

mstavale · Answer

Well, even though I can get this to work on my 6024f routers, it will not work on my 3348 switches.

braybk · Answer

Yeah, I never got it to work either, for whatever reason.  I ended up buying a set of remote addressable power strips so that I can just call up the power strip and cycle power to the switches.  A bit pricey, but they work from anywhere I can use a phone.   -Bryan

MarkVDB · Answer

I was able to use typical Cisco DB25 'modem' and DB9 'terminal' adaptors (Cisco P/N CAB-5MODCM and 74-0495-01 respectively), along with a Cisco serial console configuration cable (blue or black typically) p/n 72-1249-01 and an external USRobotics Sportster 56K fax Modem (model# 325686-01 0701). I also got it to work with a Hayes Accura 288 V34+FAX (model# 5901US) and an old AT&T 9600 modem. Other external modems 'should' work as well, but of course your mileage may vary. DIP switch settings for USRobotics Sportster (the Hayes Accura 28.8 modem doesn't have external switches): DIP# = PURPOSE (POSITION) 1 = DTR set to override (DOWN) 2 = Verbal result codes ON (numeric OFF) (UP) 3 = Suppress result codes (UP) 4 = No echo, offline commands (DOWN) 5 = Auto answer enabled (UP) 6 = Carrier detect override (DOWN) 7 = Load NVRAM defaults (UP) 8 = Smart Mode (DOWN) Use the following AT commands to configure the modem profile: AT&F0 = Load factory defaults for modem. AT&N6 = Set maximum communication speed to 9600 Bits-Per-Second, as most console ports can only communicate at this speed. AT&K0 = Disable flow control. ATS0 = Set modem to auto-answer on second ring. AT&D0 = Ignore Data-Terminal-Ready (DTR) ATE0 = Disable echo, you wonâ??t be able to see what you're typing after entering this command. ATQ1 = Disable result codes, again you won't see what your typing nor will you receive a response from the modem after entering the command. AT&W0 = Store the current modem configuration in NVRAM as profile 0. AT&W1 = Store the current modem configuration in NVRAM as profile 1. AT&Y0 = Select profile 0 to be loaded on power up. AT&Y1 = Select profile 1 to be loaded on power up. NOTE: The Hayes didn't like the AT&N6 command, go figure its part of the Hayes AT Command set! Regardless, the modem still worked. I'm able to remotely dialup to the CONSOLE port on my Dell PowerConnect 3324 and gain access and configure as if I were directly connected. Similar to how I connect to the AUX port on a Cisco router or on the CONSOLE port of a Netscreen appliance. The Dell User Guide and Quick Start manual for the PowerConnect 3324 does not describe modem support. But it certainly is capable. Hope this helps! Regards, MarkVDB

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Connect external modem to 3024 console port

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