Unanswered Question
Aug 4th, 2009


My self Dipak, We had 24MB pipe we are daily faced issue related to link utilization, we sniffs the traffic and found that there were more FTP traffic

I wants to configure QoS for the same, and I wants to allow only 2mbps for FTP, when link heavily utilize.. Is it possible??

If yes please provide me the template configurations or any article.

Thanks in advanced.


I have this problem too.
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Istvan_Rabai Wed, 08/05/2009 - 04:23

Hi Dipak,

This is a sample configuration:

class-map FTP

match protocol ftp

(Other traffic types may also be defined)

policy-map TEST

class FTP

bandwidth 2000

class class-default

bandwidth 22000

interface s0/0

bandwidth 24000

max-reserved-bandwidth 100

service-policy output TEST

This configuration will reserve a 2Mbps bandwidth for FTP traffic, but ftp will be able to use more bandwidth when available bandwidth exists.

Also, the configuration under 'class class-default' will guarantee all the remaining bandwidth for any other traffic types in case congestion exists.



dipakpvaghela Thu, 08/06/2009 - 13:02

Thanks for your reply, but I want when my link is fully untallied at that time only 2mbps allow for FTP traffic and rest of ftp will drop. In normal utilization FTP user can access more than 2 MBPS.



Istvan_Rabai Thu, 08/06/2009 - 20:54

Hi Dipak,

This configuration will guarantee 2Mbps bandwitdth for FTP in times of heavy utilization of the link.

In normal utilization FTP users can access more than 2 Mbps.



dipakpvaghela Tue, 08/11/2009 - 00:40

Hi Istvan,

We don't wants guarantee 2Mbps bandwidth for FTP, But when link utilization reach up to 20-22 MBPS only that particular time FTP get 2MBPS bandwidth and remaining FTP traffic packer are drop. Coz my other application should not affect because of FTP. So pleas provide me configuration for same.



Istvan_Rabai Tue, 08/11/2009 - 08:38

Hi Dipak,

The configuration offered by me does guarantee a 22 Mbps bandwidth for the Other applications.

FTP will not affect the Other applications.

The Class Based Weighted Fair Queue works by dynamically allocating the available bandwidth among the different traffic types, the following way in this particular configuration:

When there is congestion, and your Other applications use a lot of bandwidth, they will have a guaranteed 22 Mbps bandwidth.

When there is no FTP traffic, the Other applications can even have 24 Mbps bandwidth (the full bandwidth).

However, when there is FTP traffic and Other applications traffic as well, the 2 traffic types will share the bandwidth according to this configuration: FTP will have a maximum of 2Mbps guarantee, and the Other applications will have a maximum of 22 Mbps guarantee.

The FTP traffic above that bandwidth will be dropped, and eventually the TCP window size will be reduced and FTP traffic slows down.

When there is only FTP traffic, FTP can have even more bandwidth, up to 24 Mbps (full bandwidth).

But if traffic from Other applications comes again, FTP traffic will give up that 22 Mbps bandwidth to the Other applications, and FTP traffic will consume a maximum of 2 Mbps bandwidth.

The Other applications are guaranteed to have a 22 Mbps bandwidth.

This way the 2 traffic types will again share the available bandwidth.

So the CBWFQ queueing mechanism is very flexible in order to fully utilize the available bandwidth, but at the same time provides bandwidth guarantees to the different traffic types during times of congestion, according to your configuration.

The different traffic types can use more bandwidth than their guaranteed bandwidth, but only when there is free bandwidth available.

If there is no free bandwidth available, all traffic types will have their guaranteed bandwidth only.

I hope my explanation is clear.

Please tell me if you need more explanation.




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