Shaping Average / Peak vs. Policing

July 5, 2006 @ 12:42 pm · Filed under CCIE Study

Greetings, Joe. You also have the CAR options…. check, “rate-limit” on the docCD.
Dave Schulz Email: dschulz@dpsciences.com

—–Original Message—– From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Joe Gagznos Sent: Tuesday, July 04, 2006 8:44 PM To: ccielab@groupstudy.com Subject: Shaping Average / Peak vs. Policing
I am trying to find another way to limit outbound traffic through an interface similar in manner to policing. I understand that functionally the two are different. With shaping you are going to be queuing excess traffic to a predetermined rate where with policing you are going to be executing some kind of action on traffic that exceeds the contract (usually dropping).
For comparison purposes, I have configured shaping and policing on two separate subinterfaces in the following manner:
interface Ethernet0/0.1 encapsulation dot1Q 10 ip address 10.1.1.1 255.255.255.0 service-policy output shape
interface Ethernet0/0.2 encapsulation dot1Q 20 ip address 10.1.2.1 255.255.255.0 service-policy output police
Both interfaces are configured to limit traffic to no more than 2.5 Mbps as follows:
policy-map police class class-default police 2500000 conform-action transmit exceed-action drop
policy-map shape class class-default shape average 2500000
What I find is that the shaping interface initializes the parameters as follows:
R1#sh policy-map interface e0/0.1 Ethernet0/0.1
Service-policy output: shape
Class-map: class-default (match-any) 19 packets, 1729 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: any Traffic Shaping Target/Average Byte Sustain Excess Interval Increment Rate Limit bits/int bits/int (ms) (bytes) 2500000/2500000 15000 60000 60000 24 7500
Adapt Queue Packets Bytes Packets Bytes Shaping Active Depth Delayed Delayed Active - 0 19 1729 0 0 no
A couple things to note here - Be is initialized to the same value as Bc of 60000 (or 7500 bytes). The byte limit is 15000 bytes, though. This must mean that the byte limit is initialized to Bc+Be=15000. With a 24 ms interval, does this mean that the interface will send 5 Mbps (15000 * 8 bits / byte * 1 sec/.024 = 5000000) instead of the contracted 2.5 Mbps? If shape average is allowing the interface to transmit Bc+Be each interval, then how does this differ from configuring shape peak which accomplishes the same thing?
With policing it appears that things are much more straightforward.
R1#sh policy-map int e0/0.2 Ethernet0/0.2
Service-policy output: police
Class-map: class-default (match-any) 107 packets, 7473 bytes 5 minute offered rate 0 bps, drop rate 0 bps Match: any police: cir 2500000 bps, bc 78125 bytes conformed 63 packets, 4305 bytes; actions: transmit exceeded 0 packets, 0 bytes; actions: drop conformed 0 bps, exceed 0 bps
Thanks for any response!
Joe Gagznos