Limit bandwidth on DS3

Unanswered Question
Feb 19th, 2008

How can I limit the bandwidth on a DS3? Are there several options to satisfy this goal? I am wanting to test some wan optimization solutions, but am curious if we can cut back the bandwidth and still see the same or better performance.

Routers are 3845.

I have this problem too.
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shivlu jain Tue, 02/19/2008 - 10:46

On DS3 you can use the CAR.

The example illustrated below limits the rate by application:

•All World Wide Web traffic is transmitted. However, the IP precedence for Web traffic that conforms to the first rate policy is set to 5. For nonconforming traffic, the IP precedence is set to 0 (best effort).

•FTP traffic is transmitted with an IP precedence of 5 if it conforms to the second rate policy. If the FTP traffic exceeds the rate policy, it is dropped.

•Any remaining traffic is limited to 8 Mbps, with a normal burst size of 16000 bytes and an excess burst size of 24000 bytes. Traffic that conforms is transmitted with an IP precedence of 5. Traffic that does not conform is dropped.

Notice that two access lists are created to classify the Web and FTP traffic so that they can be handled separately by the CAR feature.

router(config)# interface xyz0/0/0

router(config-if)# rate-limit input access-group 101 20000000 24000 32000

conform-action set-prec-transmit 5 exceed-action set-prec-transmit 0

router(config-if)# rate-limit input access-group 102 10000000 24000 32000

conform-action set-prec-transmit 5 exceed-action drop

router(config-if)# rate-limit input 8000000 16000 24000 conform-action

set-prec-transmit 5 exceed-action drop

router(config-if)# ip address x.x.x.y


router(config-if)# access-list 101 permit tcp any any eq www

router(config-if)# access-list 102 permit tcp any any eq ftp



Joseph W. Doherty Tue, 02/19/2008 - 11:54

You can configure a CBWFQ outbound shaper to mimic a smaller pipe.

E.g. (syntax might be off)

policy-map yourname

class class-default

shape # (bps, I think)

serial x

service policy yourname output

If you also want to reduce inbound, best done on far side's outbound.

Mohamed Sobair Tue, 02/19/2008 - 12:35


Its bandwidth limitation, if you limit the bandwidth & utilizes it , then it will impact the performance of the Network unless you then implement Congestion Managment to priotrize specific Traffic Over another.

As for limiting your bandwidth, u could acheive that by implementing Policing:

class-map match-any limit

match access-group 100

access-list 100 permit ip any any

policy-map limit

class limit

police (Your desired bandwidth) conform action transmit exceed action drop

int x

service policy output limit



Paolo Bevilacqua Tue, 02/19/2008 - 13:21

Well, first of all you've to check which kind of service you've subscribed.

If it is point-to-point leased line DS3, telco cannot give you subrate, it's all or nothing.

If it is tow DS3's to the internet, your ISP could be giving you subrate on one or both sites.

If it is ATM or Frame-Relay, beside the access-speed what matters is the contracted PVC speed (CIR or SCR).

So you've to be specific when saying "wan ds3".


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