For TCP traffic you want to use: 1) 1518 bytes * (window size * 2) 2) rate / 8000
Whichever is HIGHER. The minimum is 8000 bytes on the 3550. You want to use this so that the policer does not take effect before TCP flow control kicks in. The formula uses 8000 because the policer uses a 0.125ms policing interval, so there are 8000 of these in one second, which is what your rate is measured in. So, for 3Mbps your burst would be 375 bytes, which is below the minimum configurable value of 8000. If you want to take TCP window size in consideration, then the burst would be 64512 (Windows XP, at least on my machine) * 2 * 1518 = 195,858,432 bytes. Sounds ridiculous. Even a 16K window size would be about 50MB. I don't get the 1518 * (window size * 2) formula, but that was the formula in one of the Networkers troubleshooting sessions. Then again, I went to all three troubleshooting sessions (2900/3500, 4500, and 6500) and in each and every one of them the presenters explained how to calculate the burst rate differently. The 3550 was the one with that formula though. The 6500 used rate / 4000, so I assume it's policing interval is 0.25ms instead of 0.125ms. Take a guess and go with it. ;-) Fred Reimer - CCNA Eclipsys Corporation, 200 Ashford Center North, Atlanta, GA 30338 Phone: 404-847-5177 Cell: 770-490-3071 Pager: 888-260-2050 NOTICE; This email contains confidential or proprietary information which may be legally privileged. It is intended only for the named recipient(s). If an addressing or transmission error has misdirected the email, please notify the author by replying to this message. If you are not the named recipient, you are not authorized to use, disclose, distribute, copy, print or rely on this email, and should immediately delete it from your computer. -----Original Message----- From: Erek Riccobuano [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 06, 2003 3:48 PM To: [EMAIL PROTECTED] Subject: 3550 Policing [7:73627] I want to police traffic on a 3550 so that one port is set to 3Mbs another is 10Mbs and another is 1.5Mbs. How do I calculate the burst? The CCO give a formula like below but I can't make sense of it. Burstmin (bits) = Rate (bps) / 8000 (1/sec) My configs so far are below. Am I going about this the right way? All I want to do is limit each customer to the bandwidth agreed upon. access-list 100 permit ip any any class-map match-all customer1 match access-group 100 policy-map customer1 class customer1 police 3000000 ???? exceed-action drop interface FastEthernet0/16 service-policy input customer1 Thank you, Erek **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=73632&t=73627 -------------------------------------------------- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
