Rate limiting

Unanswered Question
Dec 13th, 2007


I've got two routers connected by ethernet to each other.

Whereas I want to simulate a 1Mbps link between these two I have put a 1meg rate limit as input & output in connecting interfaces.

rate-limit input 1000000 ....

rate-limit output 1000000 ....

The problem is when I tranfer a file between these two (I've a web server behind one) , the downloader can't go faster than 35KB!!!!

I expected at least 100KB without the burst which would also allow more!!!

Is there anything wrong with my idea to simulate a 1mbps link between these two routers.


I have this problem too.
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Overall Rating: 5 (1 ratings)
mheusing Fri, 12/14/2007 - 03:37


The problem you create is because of the policer dropping packets, which does affect TCP throughput. TCP throughput is roughly window size/round trip time and window size is halfed, if a drop is experienced.

Change your configs to use a shaper, which is much closer to a 1Mb interface, as it will queue traffic like every normal interface does as well.


policy-map Shape1Mb

class class-default

shape average 1000000

interface Ethernet0

service-policy output Shape1Mb

Apply this policy on both routers outbound and test again. Should be much better.

Hope this helps! please use the rating system.

Regards, Martin

vanguard1 Thu, 12/20/2007 - 10:52

Martin, just wanted to thank you for this info. Very straight-forward and useful. Just setting up my remote sites with MPLS, and have applied the above config to the interfaces facing the cloud, modifying of course for our speeds here. I will be adding voip once this is setup. Any tips regarding voice. Would the qos be done on the switch providing poe, and not on the switch connecting to the mpls cloud. Voice would be highest priority. Looking forward to your response.


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