Another CSU/DSU thread

Unanswered Question
Dec 10th, 2009

OK so first off I have not been to any cisco type of training school.  I'm sure the obvious answer is, "Well then go to one instead of asking all of us here then! =P

I have 2 cisco 2801's with CSU/DSU module in it.

I can interface the unit fine from the console port or by using the web based java enabled SDM 2.5 software.

I have setup the CSU/DSU using the console interface inputting:



NO (to fractional T-1)

no IP was configured into this serial device either.

I also have my FE 0/0 connection setup in Full duplex

Now, I have a homeade T1 crossover cable inputted into the CSU/DSU of each router.  There are no alarm lights on either CSU and the CD light is green.

Thus telling me my connection between the two units via the "T1" link is good.

I can ping the router that is attached to either computer via ethernet just fine, but I cannot ping the other router attached via the "T1" link or the other computer attached to the other router.

Something like this:

Computer 1 <----> FE 0/0 (Router 1) <--??--> CSU/DSU (1) <---->HOMEADE Crossover cable (w/pins 1,2 & 4,5 reversed on one end)  <----->CSU/DSU (2) <--??--> FE 0/0 (Router 2)<--->Computer 2

The question marks are there because I cannot ping computer 2 from computer 1 or vice versa.  How can I tell if I have good connectivity from my routers FE 0/0 port to the CSU/DSU of the same router?

I mean it's not like I can ping it right?

Just throw out ideas on what you think I might be able to do to resolve this if you guys get a chance.

Thanks in advance for any help.

I have this problem too.
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Ronit Bhattacharjee Thu, 12/10/2009 - 13:51


Can you add a "show run", "show controller t1" / "show service-module", "show interface" from both the routers?

edkinj888 Thu, 12/10/2009 - 14:53

I will work on some of those but I've run into another problem now.

First, it seems my 2nd router isn't holding the setup information.  Could this be due to a defective NVRAM chip?  Or could it be that my IOS has become corrupted and needs to be reinstalled?  I figured most of this stuff was kept on the Compact Flash Card but figuring doesn't give me the real answer.  Currently I am running 12.4(3f) and it is no longer downloadable.

I've been to some page where I can download some MD IOS file also called Mainline?  Is this the correct file I would want to download if I wanted to update/reinstall the IOS on my router? The latest 12.4 rev level for a 2801 looks to be 25b. Of course I do not have a current Agreement for this router so is there anyway I could pull the IOS off of the other router?

A couple of other things.  Some of those commands post my passswords so I need to go through the logs and verify none of those show up.

Secondly when I did happen to run
"show controller t1"

NOTHING came up.

I'll get back to you with all the other stuff in a bit.

Thanks for the quick reply.

BTW I'm NOT looking for free IOS downloads.  I just want to get this thing working in it's most basic function so I don't have to climb a 11,000ft mountain every time the stupid power goes out.

edkinj888 Thu, 12/10/2009 - 15:56

cisco bad boot sequence.bmp

cisco good boot sequence.bmp

So here are the two boot sequences I pulled off hyperterm.  The bottom one has no issues saving configurations the top one won't even save the configuration when it just got inputted 10 seconds ago.

I should probably move this portion of the thread elsewhere huh?

edkinj888 Thu, 12/10/2009 - 15:58

So here are the two boot sequences I pulled off the routers.

See how the bad one has more information between the startup sequence portion before the compact flash card is accessed?

Ronit Bhattacharjee Fri, 12/11/2009 - 01:22

What do you mean by "router does not hold configuration"? Does it go back to default configuration on reload? If so, your config register

might be set incorrectly. it should be 0x2102 for the router to load the configuration on boot. You can see the config register value  in "show ver"

the command would be "config-register 0x2102" in global config mode or something similar (use tab)

edkinj888 Fri, 12/11/2009 - 07:27

Yes.  If I configure the machine then reboot it the configuration is now gone.

BUT the other thing is if I configure the machine and then use it I still cannot access it via the SDM program.  Meaning that even after I JUST configured it, the darn thing is not retaining the config for some reason....

Paolo Bevilacqua Fri, 12/11/2009 - 07:30

You have been told why the router does not keep configuration.

Do yourself a favor anf stop using SDM. It prevents you from learning and produces confusing an buggy configurations.

edkinj888 Fri, 12/11/2009 - 07:46

p.bevilacqua wrote:

You have been told why the router does not keep configuration.

Do yourself a favor anf stop using SDM. It prevents you from learning and produces confusing an buggy configurations.

Did I say something wrong in my previous post?

I'm not using SDM to try and configure the router I'm using SDM as a tool to verify that the router is maintaining its IP address info.

Which it is not.

Ronit Bhattacharjee Fri, 12/11/2009 - 07:56

I am not sure how SDM reads the configuration but did you try what I mentioned in my previous post? Also,

can you compare a "show start" and "show run" immediately after a "wr mem"?

edkinj888 Fri, 12/11/2009 - 09:24

Allright so the config-register was totally at some other point 0x804? iirc.  Anyway got that changed and now it boots great.

So now that we are back on track I am still at the point where my CSU/DSU's are not allowing me to cross communicate between both routers.

I'll look back at yoru earlier posts and post some screens from Hyperterm (as I am unsure as to how to pull the data out of hyperterm that isn't all gibberish) on what you requested before the memory config problem.

Really apprieciate all the help you are giving me m8.

Paolo Bevilacqua Fri, 12/11/2009 - 09:37

always use putty, never hypertem.

Then you take "show controllers t1", post together with config.

Note the crossed cabel must use T1 pinout, NOT ethernet.

edkinj888 Fri, 12/11/2009 - 09:46

p.bevilacqua wrote:

always use putty, never hypertem.

Then you take "show controllers t1", post together with config.

Note the crossed cabel must use T1 pinout, NOT ethernet.

I am currently using this pinout with the TX and the RX reversed on the second plug

T1/E1 Pinout (RJ-48C)

T1/E1 wiring may use either a RJ45, DB15 or BNC connectors. The pinout shown uses RJ45 connectors - its formal name is USOC RJ-48C and is defined in ANSI T1-403-1989. T1 is a North America (primarily) digital service providing 1.544 Mbps. E1 is a European/Rest of World standard providing digital service at 2.048 Mbps. CATegory 5(e) cabling is used to provide balanced pairs. The color coding for Cat 5(e) cabling may be 568A or 568B.

RJ45 PinSignalNotes
1RX1 (Ring - negative)
2RX2 (TIP - positive)
3FGND (RX GND)Ground/Shield
4TX1 (Ring - negative)
5TX2 (TIP - positive)
6FGND (TX GND)Ground/Shield
edkinj888 Fri, 12/11/2009 - 09:40

Here is the show service-module and show interface for the first router  The other thing is when i type show interface t1 it returns nothing.  no errors stating that i typed it wrong.  Just a return line and then the router# waiting for me to type something.

I really hope the SS's aren't innapropriate for the advice you are giving me.  Meaning - instead of being able to see one long stream of info all you see is a interrupted sequence...

Let me know if it's a pita maybe I can figure something else out.

Ronit Bhattacharjee Fri, 12/11/2009 - 09:46

This doesn't give us much information except that the interfaces are up and should be able to ping. Capture a "show tech" from bo

th the routers and upload.

Do a "term len 0" and then turn on text capture using the instructions in the following link

Once the capture is done, do a "show tech" which would dump all the information into a text file. Follow the same for the other router and upload.

Ronit Bhattacharjee Fri, 12/11/2009 - 10:35

I am not sure what we're looking for here. The interfaces are controllers are all up. here's the interface config

uration for Pajarito

interface Serial0/1/0

no ip address

bridge-group 1


here's the config for LDCC

interface Serial0/1/0

no ip address

Where are the ip addresses? Can we try something like this?



here's the config for LDCC

interface Serial0/1/0

ip address

interface Serial0/1/0

ip address

no bridge-group 1

edkinj888 Fri, 12/11/2009 - 10:40

you want me to put ip addresses into the CSU/DSU's of either router which are 192.168.1.X

where X is:

1- for pajarito


2 - for LDCC?

Ronit Bhattacharjee Fri, 12/11/2009 - 10:47

You would know what ip address to use. What are you trying to accomplish here? The serial is just like any other link. Would work the same as Fa links.

edkinj888 Fri, 12/11/2009 - 10:57

I want to talk from one computer to another computer

eg:current computer IP addy is

second computer IP addy is

I want to ping computer 1 from computer 2

I am trying to enable a link from a 10000ft mountain with snow and ice at the top to a warm cozy building with hot chocolate.  So that when I have to come up here for an on call situation to reset something, I won't have to climb up a 10000ft MTN to do it.  I can jut do it through the ethernet connection that I have setup.

I want the dumbest easiest setup of a CSU/DSU module to talk through a standard ESF B8ZS T1 connection via the fast ethernet ports 0/0 on either router.

does that make sense?

O and btw you idea did change something as now instead of pinging and receiving REQUEST TIMED OUT I now get Destination host unreachable!

seems like we are getting closer.

Paolo Bevilacqua Fri, 12/11/2009 - 09:46

Do not include bmp. Use putty, copy and paste directly here.

networking has its own rules, one is always use right tools and procedures, another is you often learn more reading and trying than asking others.


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