A real life situation here with Serial Int.

My boss, the network admin, is trying to install a new router so that we can set have two T1 lines coming in in what he said is a 2 x T1 configuration. He said that he thinks something is wrong with the router because because when he issues the no shutdown command on the Serial interface it won't keep. I asked him if it was connected to the CSU because from what I understand if you don't have clocking for the interface it won't stay up. He's thinking it might be something as extreme as the motherboard, but I'm thinking maybe I could be the hero and go in and figure it out. Do I have to specify that clocking is to be provided by the CSU or is that automatic?

Any ideas?

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Comments

Humper

Is the line up and protocol down?

Clocking is supplied by the CSU/DSU usually. Have you checked the cables? If its PPP then make sure that it's authenticating properly (debug ppp authentication). Im guessing you've checked with the ISP to make sure that the line is 'up' to the demarc?

If line is down protocol is down it's physical problem.

bmauro

If the router is the DTE then you do not need to specify the clock rate.

At least in my home lab the interface can detect if a DCE cable or a DTE cable is plugging into the serial int. Clock rate is set on my DCE serial and all is good. Hope this helps.

Humper

bmauro wrote:

If the router is the DTE then you do not need to specify the clock rate.

At least in my home lab the interface can detect if a DCE cable or a DTE cable is plugging into the serial int. Clock rate is set on my DCE serial and all is good. Hope this helps.

In a home lab, you need to set the clock rate on one of the routers with the clock rate command. One router is the DCE the other is the DTE.

With a provider the DCE is the telco's DSU/CSU and your router is the DTE.

bmauro

I'm going to piggyback this question onto this thread.

In every book I've read for CCNA they all say the same thing - that a RS232 (or similar) is connected to an external CSU/DSU and the CSU/DSU is responisble for the clocking. Every router I've worked with at work has an internal CSU/DSU...... So where is the clocking there? I've looked at the config files and I've never seen the "clock rate" command used at all.

Humper

They dont use the clock rate command, its another one let me see if I can dig it up..

T1 CSU/DSU Configuration
Set one CSU/DSU to clock source internal, and the other CSU/DSU to clock source line. The linecode, framing, data-coding, and timeslots must be set the same on both CSU/DSUs.

From Cisco.com. This setup is used if you want to do back-to-back T1 DSU/CSU config in your home lab.

bmauro

Well the serial int is going to a frame relay circuit - and I'll be the first one to say that I don't know enough about how frame relay deals with such things (only getting ready for Intro)

Sorry to get this thread sidetracked

Humper

bmauro wrote:

Well the serial int is going to a frame relay circuit - and I'll be the first one to say that I don't know enough about how frame relay deals with such things (only getting ready for Intro)

Sorry to get this thread sidetracked

Well if its a FR circuit then the DLCI's have to be configured.

keenon

i have a few questions to start

what type of router?
what ios is on it?
the t1 that your adding is going into a new router or the same router?
what is the type of circuit frame or ppp?
are you trying to multiplex/bond these circuit? ( take 2 circuits and make them act as 1)

mobri09

Brian,
I will explain all of this to you first thing tomorrow morning at work.

hectorjhrdz

i don't think that the problem is the clock.
the sync is given by CSU/DSU

check out if the IOS version supports T1 modules and the compatibility of the router's processor with IOS.

luck!!!!