Early Vid: Dialing into Cisco Routers
Added 2025-01-15 16:43:40 +0000 UTCA very early pre-release — I'm out of town for a long weekend so I wanted to get ahead of it. Video goes live Friday!
This one was an adventure — trust me when I say I tested a massive matrix of combinations across all the modems I had, but only had luck locally in the workshop, as you'll see. Let me know what you think!
Comments
Addendum: - CD is also known as DCD (Data Carrier Detect) - DCE stands for Data Circuit termination Equipment I found this info in the following video by Ben Eater: https://youtu.be/AHYNxpqKqwo From https://www.ardent-tool.com/Cisco/port-pinout.pdf I conclude:: - DCD on the DCE should be connected to DSR (pin 7) on the AUX port.
Marcus von Cube
2025-01-19 11:27:16 +0000 UTCthanks for the extra info! I'll troubleshoot some more and post an update eventually
clabretro
2025-01-18 21:40:46 +0000 UTCThis is a copy of my YT comment (@mvcube) on the modem video: Never trust a premade cable or adapter! Troubleshooting serial connections almost always requires a simple breakout box that goes between the DB25 socket and plug. It's nothing more than a bunch of LEDs and possibly jumper cables to reconfigure the connection. To connect a DTE (Data Terminal Equipment, the router) to a DCE (Data Communications Equipment, a modem), you need to connect GND, Rx, Tx, RTS, CTS, DSR, DTR, CD and RI all straight through (that's one more than an RJ45 plug can provide; at least one signal must be missing from the router). CD (Carrier Detect) is important because it tells the DTE that the connection is finally established. RI (Ring Indicator) allows the DTE to answer calls whithout resorting to the auto answer setting of the modem. RTS and CTS were originally meant to turn on the transmitter hardware (Request To Send) and signal back its state (Clear To Send). They're typically used for hardware handshake in later implementations like smart modems. DSR and DTR are more or less static signals to indicate that the devices are turned on and ready. Smart modems are special because they can autodetect the baud rate of the serial interface by monitioring the receive line for the "AT" command. The speed between the modem and the DTE is independent from the connection speed over the telephone line. Some modems even add data compression to the latter. This makes handshaking between the DTE and the modem absolutely neccessary. It's always a good idea to set the DTE baud rate to a higher value then the actual connection speed. As others have already pointed aout, in order to troubleshoot the runaway Rx/Tx blinking you should check for local echo settings on each side of the connection. This may create a tight feedback loop, just like a microphone close to a speaker. You can debug this by feeding one of the data lines to an additional serial interface and use a terminal application to monitor the data. Maybe you should hunt for an actual line monitor which might come handy in other cases, too. Marcus
Marcus von Cube
2025-01-18 09:33:25 +0000 UTCI heard you say in one of your videos that you were looking into setting up a DSLAM? I still have an Alcatel Speedtouch USB ADSL modem lying around, it used to work here in Europe, don't know if it will work in the US, but if you want it I can send it over to you?
Cedric Roijakkers
2025-01-17 18:45:03 +0000 UTCIt's definitely possible (you can see I was trying out different adapter configs towards the end). Just super odd that it worked sometimes with some of the modems!
clabretro
2025-01-16 18:19:01 +0000 UTCAlso, with the 2500 and 1700 series routers, they used to come with two RJ45 to RJ45 cables, one blue and one black. The black one was always in a bag labeled AUX and the blue one was in a bag labeled CONSOLE. There was usually one of those DB25 to RJ45 adapters labeled MODEM too. I don't have any of the black cables to compare anymore, but I wonder if there might have been a minor pinout difference compared to the standard blue rollover cable.
John Bailey
2025-01-16 01:45:50 +0000 UTCI think your 25-pin to RJ45 adapter may have two of the pins reversed. I forget which two. Cisco had their own 25-pin adapters to connect to the rollover cable to a modem. Those were always labeled "MODEM", usually with a white sticker but sometimes with the word molded into the shell. Funny enough, I have the exact same V.92 modem, bought in Ohio, and I think the box had the French text on it when I bought it too. I can't confirm though as I got rid of the box long ago. Also, the 9-pin to RJ45 cables HP supplies with their Aruba and HPE switches is properly wired through that you can use it with a Cisco AUX port to be an additional console port. That's SUPER helpful on the routers with replaceable flash SIMMs to load an IOS image via XMODEM.
John Bailey
2025-01-16 01:34:41 +0000 UTCAT&T still supplies US Robotics 56k modems and cabling to their managed router customers. The customer is REQUIRED to have the modem connected to a dedicated POTS line so that AT&T can manage the routers out of band. They test it periodically and if they can't reach the modem, the customer gets a warning and a limited amount of time to get the modem accessible again or the service connected to the router will be terminated. I ran into that last year when the POTS line connected to our modem lost dial tone without us realizing it.
John Bailey
2025-01-16 00:44:39 +0000 UTCThe docs strongly recommend hardware flow control. I did try both though — and for what it's worth the times it worked with the hayes modems it was on hardware. I was always able to reverse telnet into the modem attached to the router and interact with it. Very strange. I think I probably just need to bring that 2509 in here so I can rapidly experiment and follow the Cisco doc again.
clabretro
2025-01-15 21:14:14 +0000 UTCOK, that makes more sense. Did the docs call for both hardware and software flow control? I would think that one or the other would be good enough. You might consider testing with computers on each end through the modems to make sure you car connecting OK. You may be able to get better diagnostics until you get a solid connection that way, then put the router on one end.
Jack Beckman
2025-01-15 21:12:27 +0000 UTCI didn't realize this until later and didn't cover it in the video, but it eventually settles down. It's like the router is trying to interact with the modem for ~2-3 minutes and eventually stops (even when the router isn't configured to auto-discover). Every time I was able to get it to work either with the 1200 or 9600 the read/send lights were off right away and weren't blinking. Very odd!
clabretro
2025-01-15 21:05:00 +0000 UTCThe modems all showing activity just having that cable hooked up make me think some wires are not right. You may want to continuity test to see if those cables are wired the way you think they are.
Jack Beckman
2025-01-15 20:57:15 +0000 UTChaha. that sounds like a cool setup! let me know how that leased line goes!
clabretro
2025-01-15 20:49:27 +0000 UTCThese episodes really should start with "do not try this at home" :p This video has led me down a rabbit hole! I've just bought 2 MultiTech MT2834BL modems on eBay which also have an option for "leased line mode". It should be fun getting them setup to connect 2 Cisco routers together over a leased line :D
John Osborne
2025-01-15 20:41:46 +0000 UTCYou're right! Modem upload has always been capped at 33.6 but ISP's applied compression to downloads to bump it to 56K. The best you're going to get through an ATA is 33.6 (from my experience). I'm sure more knowledgeable people will chime in.
vivi
2025-01-15 18:08:02 +0000 UTChaha
clabretro
2025-01-15 18:01:25 +0000 UTCI'm sure more knowledgeable people will chime in, but I think I've read that 56k can be a bit of a pain to deal with and that 33.6 is better for certain usecases that doesn't involve downloading mp3's off kazaa.
Martin Paulsen
2025-01-15 17:58:31 +0000 UTClove it
clabretro
2025-01-15 17:38:48 +0000 UTCYou think these aren’t used any more, but they are. We still have POTS lines going into some of our Cisco gear so we can get to it should the poop ever really hit the fan.
Jonathan Cilley
2025-01-15 17:35:16 +0000 UTC😇
clabretro
2025-01-15 17:32:53 +0000 UTChaha that's awesome! I almost whipped out the custom ethernet-to-four-phone-ports cable splitter but cheated with an actual phone line I had ran ha
clabretro
2025-01-15 17:32:33 +0000 UTCSo like, I'm currently drowning in work and you have to release this kick-ass video doing exactly what I want to do with my 2620.... which is currently staring at me from the other end of my desk. I'm a little mad tbh...
vivi
2025-01-15 17:12:05 +0000 UTCAt the datacenter I work at, we just setup a brand new POTS line just for 2 cisco routers for a client (yes in 2025). They said it was required as a 3rd option to get in to them remotely if they can't via WAN/LAN and didn't want to use something like Opengear. It was fun teaching the newer techs about POTS. Blew their mind we could just use a pair out of Cat5e cable and still able to use patch panels to get it to their rack!
Nathan Marolt
2025-01-15 17:02:05 +0000 UTC
