From: Scott Morris (swm@emanon.com)
Date: Thu Jul 03 2008 - 09:15:11 ART
Yes and no.
You're correct about the Pak Priority concept in routers. That's a coding
issue. You won't see it down the line because routing protocols (IGPs) are
designed to be link-local in nature, so further routing isn't necessary.
As for switches, if you enable mls qos, you can look at the queuing details
and see that hardware queuing kicks in. I don't know as I have ever looked
to see whether the IP Prec - to - hardware queue mapping occurs if mls qos
is not turned on though....
Anyone ever looked? :) My 3750 seems to be clear about it not being turned
on.
emanon-Bellerive#sh mls qos int f1/0/1 q
FastEthernet1/0/1
QoS is disabled. When QoS is enabled, following settings will be applied
Egress Priority Queue : disabled
Shaped queue weights (absolute) : 25 0 0 0
Shared queue weights : 25 25 25 25
The port bandwidth limit : 100
The port is mapped to qset : 1
emanon-Bellerive#
Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
Senior CCIE Instructor
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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Bill
Eyer
Sent: Thursday, July 03, 2008 6:42 AM
To: Tyson Scott
Cc: Morris, Jason L.; ccielab@groupstudy.com
Subject: Re: DSCP and default PHB
I have also came across references that indicate that a routers "own"
packets for routing protocols, usually marked with ip prec 6 are queued
independently without enabling a queueing mechanism. This does not seem to
translate to the next-hop router though, in other words each router
specially queues it's own routing protocol packets but if they go through a
switch there is no special queueing. Off hand, I can't think of a way to
verify this.
Bill
Tyson Scott wrote:
> By default the DSCP field is not interpreted without turning on a
> queueing mechanism. By default FIFO.
>
> On Wed, Jul 2, 2008 at 6:15 PM, Morris, Jason L. <Jasmorris@checkngo.com>
wrote:
>
>> Just to clarify and dispel my ignorance...
>>
>> There is no 'default' 'per hope behavior' for a Cisco router or switch
>> that depends on DSCP markings? Those markings are just so you can
>> classify traffic and then manually configure PHB on each device right?
>> That's been my assumption up to this point but I was review some QoS
>> stuff in a buddies ONS - CCNP book and it inferred (or at least made me
>> question) that the router was doing something different with EF marked
>> packets without explicitly being told to...
>>
>> That's not the case right? It doesn't by default, out of the box, treat
>> differently marked DSCP traffic differently?
>>
>> Jason Morris
>>
>>
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