4500 QoS Question

[elct29]

I have a quick question regarding 4500 QoS configuration. In reading the QoS SRND Guide, it states that shaping is recommended.

"This queue can be defined to be

shaped to a peak limit, such as 30%, to allow bandwidth to be available to non-voice applications. This

would be valuable in the event that a trust boundary has been compromised and a DoS/worm attack is

saturating voice queues"

But in other posts, I've read people do not recommend using shaping. Should I use shaping or just set queue 3 as a high priority queue

This is the config I have been using:

interface FastEthernet X/X

service-policy output DBL

qos trust cos

qos trust device cisco-phone

tx-queue 3

priority high

shape percent 30

Thanx for your help

[smahbub]

If lot of voice traffic needs to be sent limiting the bandwidth to 30% would be a better option.Else we could go with setting queue 3 as a high priority queue.

[a.gooding]

From my very limited understanding of QOS (now on chapter 1 for the exam :)) it states that shaping actually slows down the packets to ensure that packets are not lost.

ive also read( dont kill the messenger) that using PQ starves non priority traffic and is not the ideal choice in queueing. using LLQ is better at queueing.