rate-limit burst

[paul amaral]

Hi, im confused on the following and hoping someone can clue me in.

I want a 1 meg connection brustable to 3 megs but I'm confused on how i should configure this using rate-limit command.

will this do the trick

rate-limit input 1000000 562500 562500 conform-action transmit exceed-action drop
rate-limit output 1000000 562500 562500 conform-action transmit exceed-action drop

i got the bc size of 562500 bytes by using the following formula 3000000 bits x 8 / 1.5 TC which is what Cisco recommends. However should i be using a TC of 1.5 i guess im not sure how the time interval works and if i can use something else besides 1.5

also if i have

rate-limit input 3000000 1532 2000 conform-action transmit exceed-action drop

rate-limit output 3000000 1532 2000 conform-action transmit exceed-action drop

does this mean i can have a combined 3 meg total traffic to the interface but the BC of 1532 bytes would cause performance issues since its not big enough and thus drop more packets?

[paul amaral]

Ok after rate-limit research here is what i found. You don't want a BC that is

too small compared to the CIR as this will cause problems including web page loading issues and fluctuating download speeds so my example below of  "rate-limit input 3000000 1532 2000 conform-action transmit exceed-action drop" the BC is insufficient for a 3 meg link. This rate-statement is saying allow up to 3 megs of traffic to fill the bucket, which has a total byte count of 1532 depending on the size of the incoming packets this BC is way too small and will not allow for 3 meg downloads if the bucket is constantly empty.

what i ended up doing was set my rate-limit like this, " rate-limit input 1000000 46875 50000 conform-action transmit exceed-action drop". This will allow the connection to burst to 3 megs because the bucket BC can hold enough tokens for 3megs because the CIR of 1000000 bits means that we can add up to that number of bytes/tokens to the bucket, so we know we are at least going to get a 1 meg and it may burst to 3 megs or  even a little bit over because of the 400000 BE.

here are the links i found helpful.

http://routersthatsuck.blogspot.com/2010/01/cisco-rate-limit-burst-voodoo.html

https://learningnetwork.cisco.com/message/129746

http://blog.habets.pp.se/2010/01/Shaping-and-policing-on-Cisco

thanks, paul