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New Member

what is "available bandwidth"?

Hi All,

I am confusing about what is "available bandwidth". In DCE, I use "clock rate 64000" to make the circuit is 64K. But when I use "show interface" command, the display have "BW 1544Kbits" how can I know the real bandwidth? And when I config CBWFQ and use "bandwidth percent" to allocate bandwidth, How should I calculate the real bit rate? should I use CIR * percentage or use minCIR * percentage ? Thank You!

Best Regards

Teru Lei


Re: what is "available bandwidth"?

In a back to back connection, with one side acting as the DCE and providing clock, the clockrate command will actually clock the line. The bandwidth command must also be used to set the correct bandwidth ie the same as the line is actually being clocked at.

This bandwidth command will not affect the actually line speed but it will affect the statistics reflected in the show interface and can affect routing decisions.

The CIR is usually set to the contracted rate from the provider which may be less than the actual speed of the access connection.

New Member

Re: what is "available bandwidth"?

Correct...but what does available bandwidth means ?????????????

New Member

Re: what is "available bandwidth"?

Hi guys,

Consider a scenario where in you have a 64 K point to point link between your HO and Remote office. You have configured CBWFQ on the remote router end, reserving 25% of the bandwidth, the selection creteria for identifying the source and destination is based on IP address. So whenever the 64 K link is idle with no traffic flowing to and fro, the available bandwidth is 64 K, but during any instance of the day if there is any other traffic(FTP,mail traffic ) flowing across the link, then the available bandwidth for the CBWFQ will be 64 Kbps minus the traffic utilized by the other traffic. The available bandwidth will be the remaining bandwidth !!

Can someone shed more light on this ??

Thanks and regards,


New Member

Re: what is "available bandwidth"?

This link should answer the question "but what does available bandwidth means ?????????????"

New Member

Re: what is "available bandwidth"?

The available bandwidth statement actually relates to the queueing method employed on an interface(The default being WFQ). What happens is as follows:

25% of the bandwidth on an interface is reserved by default for the "default" queue , this queue is used for traffic such as routing updates e.g. things that are not necessarily defined within your queueing policy.

As an example you have a 64k point to point link on which you would like to deploy CBWFQ. If you issue a show interface command you will get an available bandwidth of 48Kb/sec (75% of 64kb) , this means that your queues cannot exceed 48kb of bandwidth allocation . This could be a problem especially on low-bandwidth links , to bypass this you can issue the max-reserved-bandwidth 100 statement on the interface , this makes the full bandwidth of the interface available for your queue but you have to keep the defaults in mind when doing this. CBWFQ creates a default queue as well but you have to remember not to allocate all the bandwidth to your various queues as this would obviously leave no bandwidth for the default . A good rule is to reserve at least 10% of a link for default traffic or in turn change the max-reserved-bandwidth to 90 instead of a 100 but this would probably leave you with two default queues when using CBWFQ.

Hope this is what you were looking for.