Routing help for my lab

Unanswered Question
Oct 12th, 2008


I have 3 routers they are have 2 x WIC-1T cards in them and I want to practice routing using the IP protocals.

I want to use RIPv2 first and have bought 3 back to back DCE/DTE cables for the WAN links, now I am unsure about the clock rate settings and PPP/HDLC encapsulation.

It would be very helpful fir an example. I see many examples of clock rates but don't understand if this is like a bandwidth rate.


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Sun, 10/12/2008 - 11:31

Hello Andy,

the clock rate command provides the OSI Layer1 clock that will be used to sample user data.

One side provides the clock the other side takes it from line.

The clock rate command has to be given on the DCE side of the cable.

To check what cable is sensed on the router interface use

sh controller serx/y

it should provide this info.

A T1 is defined as:

24 DSO channel + 8kbps control channel

1 DSO = 64000

so clock rate can use

int ser0/0

clock rate 1536000


clock rate 1548000

but you could use also 1500000 if IOS allows it.

Actually, according to IOS command reference

Desired clock rate, in bits per second (bps): 1200, 2400, 4800, 9600, 19200, 38400, 56000, 64000, 72000, 125000, 148000, 250000, 500000, 800000, 1000000, 1300000, 2000000, 4000000, or 8000000.

For some synchronous serial port adapters a nonstandard clock rate can be used. Refer to the hardware documentation for specific supported Lvalues. You can enter any value from 300 to 8000000 bps. The clock rate you enter is rounded (adjusted), if necessary, to the nearest value that your hardware can support except for the following standard rates: 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 56000, 64000, 128000, or 2015232.

so the right choice is 1480000 in your case

I remember clock rates that are then adjusted by the router itself

Hope to help


whiteford Sun, 10/12/2008 - 23:51


I will use 2 x 2621 routers for starters and use my DCT/DTE back-to-back (crossover) cables, then introduce a 3rd router (1721) for a triangle setup.

So if I run "sh controller serx/y" on the DCE router, it will give me the clock rate to define?


Giuseppe Larosa Mon, 10/13/2008 - 01:31

Hello Andy,

the value is 1480000 for T1

the sh controller serx/y just helps to verify on which side the DCE cable is that is the side that needs to have the clock rate command

Hope to help



This Discussion