?
Solved

Cisco QOS - Policing

Posted on 2010-08-22
2
Medium Priority
?
660 Views
Last Modified: 2012-08-14
Hi All,

Need your help to understand what is the Token Bucket Concept? I dont understand what it really means by new tokens are added into the token bucket based on the interpacket arrival rate and the CIR. Every time a packet is policed, new tokens are added back into the token bucket.  

In the below case, is my TOken Bucket size 884000? Can you please help me to understand what really cause the exceed action to drop kick in?

police 884000 8000 conform-action set-dscp-transmit ef exceed-action drop
Thanks
Hari
0
Comment
Question by:kamalgopi
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
2 Comments
 
LVL 9

Accepted Solution

by:
Alex Bahar earned 2000 total points
ID: 33499988
You're not alone. People often get confused with policing calculations.
Your bucket size is 8000 bytes. This means you are allowed to send 8000 bytes from your bucket within Tc period.
To simplify assume you receive packets every 5 msec (0.005 sec). You add tokens at the rate of (0.005 * 884000) = 4420 bits in 0.005 sec = 552 bytes. That means you are allowed to add 552 bytes to your bucket every 0.005 seconds.
Assume you started with your bucket full. You have 8000 bytes in it. 0.005 seconds later, you received 5000 bytes in a packet. This packet conforms because you have 8000 bytes in your bucket. So set-dscp-transmit is executed. 8000-5000=3000 bytes remain in your bucket. Referring previous calculation, you add 552 bytes to your token in 0.005 secs later. Your bucket has 3552 bytes in it. Now another packet arrives with 4000 bytes in it. This is more than the bytes in your bucket (3352). So you execute exceed action drop the packet. Referring previous calculation, you add 552 bytes to your token in 0.005 secs later. Your bucket now has 4114 bytes in it. Now another packet arrives with 4000 bytes in it.  This packet conforms because you have 4114 bytes in your bucket. So set-dscp-transmit is executed. 4114-4000=114 bytes remain in your bucket. Then there is a silence of 0.5 second period you did not receive any packets. This means 552*100=5520 bytes get added to your bucket.
I hope this helps.
0
 
LVL 11

Author Closing Comment

by:kamalgopi
ID: 33508093
Fantastic. Now i have some understanding on how it works. Now i need to go and look for what is the best figure for a Bucket for a 1M Link.
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

The Cisco RV042 router is a popular small network interfacing device that is often used as an internet gateway. Network administrators need to get at the management interface to make settings, change passwords, etc. This access is generally done usi…
Quality of Service (QoS) options are nearly endless when it comes to networks today. This article is merely one example of how it can be handled in a hub-n-spoke design using a 3-tier configuration.
In this video we outline the Physical Segments view of NetCrunch network monitor. By following this brief how-to video, you will be able to learn how NetCrunch visualizes your network, how granular is the information collected, as well as where to f…
NetCrunch network monitor is a highly extensive platform for network monitoring and alert generation. In this video you'll see a live demo of NetCrunch with most notable features explained in a walk-through manner. You'll also get to know the philos…
Suggested Courses

764 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question