Serial interfaces bw and clock rate question

agustinchernitsky

Hi everyone!

Well, I've been playing with a cisco rack... actually I managed to get 4 serial links up (isn't it great? LOL!) but I realized that I don't have clear the difference between:

1.- clock rate
2.- Bandwidth

According to my study book, clock rate is used when the router has to provide signaling (ie be a DCE). Now, is this clock rate related to the serial line speed? IE: a T1 (1.544 Mbps), how would you configure it on the serial int?

Bandwidth, on the other hand, is used for routing protocols. Is this correct?

I ended up using clock rate 64000 and bandwidth 64 without knowing why exactly... and I don't like that!

Can someone show the light?

Saludos amigos!

mwgood

The clock rate command defines the physical bit rate.

The bandwidth command tells a variety of Cisco IOS functions how much bandwidth is assumed to be available on the interface. Such functions include routing protocols and QoS tools.

agustinchernitsky

So you can have 64000 bps and that is not realted with the fact that it could be a T1/E1 line?

david_r

agustin,
That is correct. Change the BW to whatever you want and the data is still going to pass over the link at the clocked rate.

agustinchernitsky

Thanks boths for clearing this out!

Netwurk

The bandwidth command doesn't change the speed of the interface or affect it in any way - its purpose is to tell other protocols how fast the link is. For the most part, this affects routing protocols (EIGRP, OSPF, etc.)

Here's a link that should be helpful.

http://www.zdnetasia.com/insight/network/0,39044847,39375724,00.htm

agustinchernitsky

Hello Guys,

Thanks for your answers... Now, just to clear my head a little more, imagine this scenario:

[C2600]-S0/0(DTE)

---

S0/0(DCE)-[C2600]

What would determine the transfer speed (bandwidth) between this two routers across a serial line? I mean, what would make this serial connection a T1, T3, etc?

Thanks amigos!

david_r

This is a 2500.

console-server(config-if)#clock rate ?
        Speed (bits per second)
  1200
  2400
  4800
  9600
  19200
  38400
  56000
  64000
  72000
  125000
  148000
  250000
  500000
  800000
  1000000
  1300000
  2000000
  4000000

  <300-8000000>    Choose clockrate from list above

Applied to your DCE interface. You can't set it to T1 but you can get close to that speed.

agustinchernitsky

Setting it to something like: 1300000 ?

Thanks David!

david_r

That depends on your router. The choices are limited and shown by the command.

agustinchernitsky

Thanks David!