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Cisco Router Setting WAN Bandwidth

Posted on 2011-02-28
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Last Modified: 2012-05-11
How do I set the badwidth of my WAN interface?  My net pipe is 100Mbit/Full Duplex but the speed is 30/30 so Id like to set the bandwidth to 30/30 and not have the system try and send the full 100 out
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Question by:TestMonkey
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by:kdearing
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You don't need to set your bandwidth.
Your system will only transfer data at the rate the other end is willing to accept.
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by:TestMonkey
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When I was at 10/10 I set my speed at 10 and duplex full, if I didnt then my upload would be 50% of the posted bandwidth of what I was suppose to have.

Im running into the issue now, 100 Full, downloads at hitting 1.7MB down, but uploads im lucky to see 500KB, same behavior before, I was told I need to set my rate limits on the interface
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by:kdearing
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Don't know what kind of firewall/router you're using, but you may need to disable/modify your QoS and/or traffic shapping configuration
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by:TestMonkey
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Its a Cisco 2921, if this were a home router I wouldnt have to do anything but its a physical cisco with a 20/20 metro fibre dedicated for a net pipe
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by:rfc1180
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>Im running into the issue now, 100 Full, downloads at hitting 1.7MB down, but uploads im lucky to see 500KB, same behavior before, I was told I need to set my rate limits on the interface

Sounds like a duplex issue

check your duplex on both ends, either set to 100-Full or Auto

You can also post show inter fast0/0 of the interfaces and we can further assist.

Billy
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by:TestMonkey
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Duplex is fine, when i set speeds it works as expected

Its Speed 100 Duplex Full ive been through all this

I know I either use Rate-Limit or QoS
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by:Mistralol
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You may need to have a look at the buffers / loss. Chances are you are flooding the buffer on the next router or switch based on what is going on.

you need to setup qos on the interface to control the output speed so that your not "blasting traffic"

Use a class map and the service policy commands on the interface. You probably want to use the shape average and set the speed's to about 90-95% of the actual amount of bandwidth you have.

http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfmcli2.html
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imanassypov earned 500 total points
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you definitely need QoS policy (in your case you need a shaper)  setup on your WAN interface.
The most basic way of achieving it is through 'generic' shaper that will encopass all of your tcp traffic:

policy-map SHAPER
  class class-default
     shape average 30000000 300000 0
     random-detect

int fa 0/1
  desciption WAN
  service-policy output SHAPER

In the configuration above, the shaper is configured for 30Mb, with burst 300kbps and burst interval of 10ms.

The reason you need a shaper is so that you even your egress traffic to the subrate you have been provisioned with, and by enabling the random-detection you avoid hitting the 'tcp synchronization' issue where all your active tcp connections slow down to a crawl and then restart at the same time which greately reduces your line utilization.


hope that helps,

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by:imanassypov
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to get back on someones suggestion to use the 'rate-limit' - it is first of all an obsolete way of configuration, which is now replaced by MQC (similar to above).

Second and more important note on 'rate-limit' - it actually configures a POLICER and not a SHAPER. Which means rather than saturating your provider's buffers and having your provider drop your excess traffic for you, you will be cutting off and dropping traffic on your interface. As you can see, it wont give you anything other than saving your provider some cpu cycles.
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by:TestMonkey
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Ill give that a run tonight!  

Now I was creating Policies but I was putting in traffic types which I didnt want to do, you nailed what I was looking for, just a straight policy that does the 30/30
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by:imanassypov
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30/x where X is inbound - you do not really control that. Ingress traffic shaping is likely done on your ISP.

What you may also want to do is some traffic analysis - as in how much of each traffic class you normally have throughout the day. It may affect how you want to fine-tune your shaper.

-igor
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by:TestMonkey
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I put in exactly what you had and it seems to upload at a max of 10Mbit, not sure why
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by:imanassypov
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please post the output of

"show policy-map interface"
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