[silversid]

What is the difference between the clock rate command and the bandwidth command?

[Jay Whale]

What is the difference between the clock rate command and the bandwidth command?

This is a very command question, and one that I've been asked many times while training the CCNA courses.
The first thing to understand between clock rate and bandwidth, is that they have nothing to do with each other at all.

Clock rate - The clock rate command is used primarily by your service provider, when you order a line from them to connect offices together, you would obviously define the speed that you wish to have the link running at. The link speed is one of the factors that determines the cost of the link from your service provider (Distance been the other major factor). The physical cables used to create the link can run at many different speeds, so there needs to be a programmable value that can set the max speed that your new line will run at. The clock rate command is the command that the service provider will use to set the speed of the link and by changing the value of the clock rate command, the link speed will change and so will your telco bill

Bandwidth on the other hand, is to inform your device what speed the line has been set to. Remember this command will not affect the actual speed, it's just a method of informing your device what speed the link should run at. The reason the value has to be defined is that the device will assume the link is running at max physical speed if the command has not been configured. For example, assume that the link speed that you have paid for from your Telco is 512k (they will have the command clock rate 512000 configured on their side), but you have the cable plugged into a synchronous serial port (max speed 2Mbps) your Cisco router will assume that the link speed is running at maximum if the bandwidth command has not been configured. This will have a negative effect on things like routing protocols and QOS (Quality of Service).

In summary, clock rate is reality, bandwidth is perception