QOS question

Unanswered Question
Sep 1st, 2008

Hi Guys,

i got 1 question regarding question. i was just wondering if anyone can help me in answering it.

I have a frame-relay link lets say 1 mb.

i wanna configure qos and for some application lets say for example telnet. i wanna guarantee banwdith 4000 bits per second. what the best way ?



I have this problem too.
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Marwan ALshawi Mon, 09/01/2008 - 16:33

lets match the telnet traffic

class-map telenet-class

match protocol telnet

policy-map fr-policy

class telnet-class

police 40000 conform-action transmit exceed-action drop

map-class frame-relay FR-MAP-CLASS

service-policy output fr-policy

go to the frame-relay interface for example

interface Serial2/0.12 point-to-point


now applied

good luck

please, ifhelpful Rate

Marwan ALshawi Mon, 09/01/2008 - 18:14

agrre with Joseph 100% :)

so u can use the same way i told u but with simpl change on the policy-map like:

class-map telenet-class

match protocol telnet

policy-map fr-policy

class telnet-class

bandwidth [the amount of bandwidth in Kbp]

map-class frame-relay FR-MAP-CLASS

service-policy output fr-policy

go to the frame-relay interface for example

interface Serial2/0.12 point-to-point


and here u got two ways to achieve Qos with frame-relay :)

if helpful Rate

Joseph W. Doherty Mon, 09/01/2008 - 16:36

If available on the platform you're going to use, CBWFQ might be the "best" method to guarantee a minimum bandwidth when there's congestion.

E.g. (something somewhat like this)

class-map match-any yourclassname

match protocol telnet

policy-map yourpolicyname

class yourclassname

bandwidth 4

interface serial 0

service-policy output yourpolicyname



I see my and Marwan's posted about the same time. You can see they are similar. One important difference, Marwan's police statement caps the maximum bandwidth for telnet at 4K. My policy defines a minimum. The two can also be used together to define both a minimum and maximum.

amitbatra Mon, 09/01/2008 - 19:01

Hi Guys,

i really appreciate your time and efforts.

But question was bits per second.

all Qos supports minimum of 8 Kbps. which is 8000 bits per seconds, and that is 4000 bits more than what i need.

police will rate-limit the traffic. and it doesnt guarantee bandwidth.

i tried on my router . i think you cannot use bandwidth on frame-relay interface. you have to use shape average instead.


Marwan ALshawi Mon, 09/01/2008 - 19:15

hi amit

about last thing

u can use bandwidth with shaping

and policy maps

this is called nested policy-map or neted Qos

so u shape the over all interface or subinterface to amount of traffic and within that amount u might want to garntee bandwidth for voip for eaxmple

if helpful Rate

thank you

amitbatra Mon, 09/01/2008 - 22:31

Dear Marwanshawi.

I know that i can use nested policy. but when it comes to guarantee bandwidth. Bandwidth command comes in the picture. and the minimum bandwidth i can guarantee is 8 kbps.

But my requirement is 4000 bits per second. which is 4kb.

this is half of what is set to be as default of the command line or minimum..

i was thinking to shape 8kbps. which i can and then nest a policy..(child-policy) and bandwidth 50% there .

Now when i do this. and do show policy-map interface se0/0

i see shaping active NO.

why is that?? any idea guys.

Marwan ALshawi Mon, 09/01/2008 - 22:42

have u tried it

in the police or rate-limt the second is the burst

so if u put like 4000 8000 it mean u have policed it to 4k with burst max 8000 which is minimum as well

but havnt tried it !

so good luck :)

What you could try is, is create a "networking class" with 8kbs as the policed amount of traffic, then create a child policy - and shape the CIR to a percentage of the overall policed amount - say 50%....so 50% of 8kbs = 4kbs.

The reason why you see "shaping active NO" is because you have not generated enough traffic over the 8kbs for the policy to take affect.


Joseph W. Doherty Tue, 09/02/2008 - 03:21

Touche about the 8 Kbps minimum!

The simple answer is use 8 Kbps since this is the configuration minimum. (Sometimes we need to work within the constraints of the device capabilities.)

Remember with CBWFQ, the unused "reserved bandwidth" will be used by other traffic, i.e. it's not lost. If there is a concern that you really want to also limit telnet to not exceed 4 Kbps, then you can also shape it or police it at 4 Kbps even within the 8 Kbps bandwidth reservation. (Although for telnet, and working with 4 to 8 Kbps out of 1 Mbps, limiting it doesn't make much sense especially since CBWFQ will guarantee bandwidth for other traffic.)

The issue of shaping not appearing active, has been addressed by the other posters, i.e. likely not enough traffic to activate the shaper.

With regard to being unable to active CBWFQ on a frame-relay subinterface, the issue is CBWFQ needs to know what the overall bandwidth it's working with. Other posts have mentioned using a hierarchical CBWFQ policy as one technique. Another, I recall(?), is using traffic-shape within the subinterface.


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