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Rate limit on serial link

i have many sites connected to our main office router....one of our remote office has got 64K link which is ocnnecting to out main office.....while going htrough our main office router i saw a config

rate-limit input 64000 2000 3000 conform-action transmit exceed-action drop

rate-limit output 64000 2000 3000 conform-action transmit exceed-action drop

!

now i understand that the default on cisco router is 2Mbps....but the question is cant we put bandwidth 64....on that perticular interface why we have used this rate limit command.....ok if we use this command the forst thing is pretty simple 64000 what does the second and third thing mean 2000 and 3000......and how we calcuate it......and why two comand one for input and one for out put.....thanks in advance

3 REPLIES

Re: Rate limit on serial link

Hi,

is this CAR config applied to a separate Serial interface with 64k?

Then the policer (rate-limit) is quite useless, because the limit through clock speed will already be 64000 bps. I would then suggest to configure

interface Serial0

ip address ...

bandwidth 64

fair-queue !WFQ, works well in most data only cases - no voip

random-detect !WRED - works well, if mostly TCP traffic across the link

you can replace "fair-queue" and "random-detect" by a MQC policy allowing for finetuning QoS settings. If this is your goal, let me know and give some more details.

Hope this helps! Please rate all posts.

Regards, Martin

Silver

Re: Rate limit on serial link

First, the bandwidth interface command is only relavent for routing protocols used in calculating metrics. It has nothing to do with controlling traffic on the interface.

The config guide for policing/rate-limiting can be found here:

http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1828/products_configuration_guide_chapter09186a00800ca594.html

A good overview of policing and traffic shaping will help you with understanding the parameters:

http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800bd8ed.html

HTH pls rate!

Silver

Re: Rate limit on serial link

As for your specific application and the parameters you are working with now, I second Martin's point. If it is already a 64k link, it will "police" itself to 64k. Traffic shaping might be a more useful tool in your case as it could help as it could smooth the traffic a bit using a queue where rate-limiting will not. Also, I have had good luck using stac compression on links of that speed. You enable it on both ends with the interface command: compress stac. It really does help a lot.

HTH

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