Share bandwidth among multiple interfaces

Unanswered Question
Aug 4th, 2010

Hi guys,

Actually I just take one step further on one of my previous questions. Christopher Gatlin was helping me on that one I hope he can shed me some lights on this one as well.


In the diagram the f0/0 is the WAN connection to the Internet and the bandwidth is 30mbps. I have 3 internal networks A, B and C. They are all on public IPs so there is no NAT/PAT. Is it possible to cerate bandwidth pool (download direction) of 30mbps and share it among the 3 physical interfaces f0/1, f0/0/0 and f0/0/1? I want to gurantee 10mbps per link when the bandwidth is fully utilized but each link can still use up to 30mbps when another two links are idle.



I have this problem too.
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tprendergast Wed, 08/04/2010 - 13:44

You can do this using QoS. Basically, it's going to come down to the policing configuration and allowing a burst of up to the maximum.

However, you only guarantee 10mbps per subnet. If the other 20mbps are not being used, then you can burst. If the other 20mbps is being used by the other subnets, you can only use whatever is free.

Difan Zhao Thu, 08/05/2010 - 10:39


Thanks for the reply. I read through the doc and I did tests on my lab router. I only have a T1 for my lab so I limited the bandwidth on each link to 500kbps. Here is my config. Do they look right to you?


policy-map PMAP_QoS
class class-default
   police cir 500000 pir 1500000
     conform-action transmit
     exceed-action transmit
     violate-action drop


interface FastEthernet0/1
service-policy output PMAP_QoS


interface FastEthernet0/0/0
  service-policy output PMAP_QoS


interface FastEthernet0/0/1
  service-policy output PMAP_QoS


When I was doing a speedtest on the config seems to work fine. However when I'm downloading things from FTP or HTTP the traffic seems to fluctuate quite a bit from 500kbps to 1.4mbps. I am kind of aware of this behavior of policing because it's not cachine or queuing anything and it affects TCP flow badly. That's way I was usually using Shaping for simple scenarios. I guess I can't use shaping in this case, can I? If I'm using Policing can I treak Bc and Be to achieve better result? Is there a doc to show how to properly set Bc and Be? Thanks!


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