RE: mls Qos

Where does it say that enabling QoS disables flow control?

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/command/reference/cli1.html#wp2710509

-ryan

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Darby Weaver
Sent: Monday, July 27, 2009 9:37 AM
To: Anantha Subramanian Natarajan
Cc: kaniyath minha; Cisco certification
Subject: Re: mls Qos

And that is another issue.

Let's put it into context.

If mls qos is not configured explicitly, then qos marking will traverses the
switch untouched. So not turning on the will not affect the flow control
bits and the switch's ability to respond.

Turning on mls qos will disable the feature.

Is everyone confident that turning on mls qos is still the correct thing to
recommend?

Hey I've been to the lab too many time myself, and sometimes (more than I
like; I went into the lab and did it my way... I guess everyone is entitled
to do it that way and have the same kind of fun I've experienced in the
lab. I don't necessarily recommend it unless you want some hardcore real
life experience at observing proctors at work.

Your choice... pre-conceived notions about what to do and not to do without
regard to your own particular lab workbook can and probably will HURT you.

Learn to read the lab and learn to perform the tasks required as required.

This might help:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.2_25_sec/command/reference/cli1.html#wp1862510

 Usage Guidelines

QoS must be globally enabled to use QoS classification, policing, mark down
or drop, and queueing features. You can create a policy-map and attach it to
a port before executing the mls qos command. However, until you enter the
mls qos command, QoS processing is disabled.

You must disable IEEE 802.3x flow control on all ports before enabling QoS
on the switch. To disable it, use the *flowcontrol receive off* and
*flowcontrol
send off* interface configuration commands.
 ------------------------------

*Note *If QoS is disabled and you enter the *mls qos *global configuration
command, this message appears:
*QoS:ensure flow-control on all interfaces are OFF for proper operation.*
------------------------------

When QoS is enabled without any further configuration, ingress traffic is
classified to best-effort without any policing. DSCP and CoS values carried
in packets are rewritten to 0. For the egress direction, all four queues are
configured with same weighted round robin (WRR) weights, and all the packets
(that have been classified as best-effort traffic) are placed at the queue
mapped to CoS value equal to 0.

QoS features at the ingress port include traffic classification (by class
map, packet DSCP/CoS, or port DSCP/CoS), policing, and possibly marking-down
or dropping out-of-profile packets. At the egress port, traffic can be also
classified (by packet DSCP or CoS assigned at the ingress port), policed,
and possibly marked down or dropped. If not dropped, the packet is placed in
one of four queues, which can be configured with tail-drop or WRED threshold
parameters.

Policy-maps and class-maps used to configure QoS are not deleted from the
configuration by the no mls qos command, but entries corresponding to policy
maps are removed from the switch hardware to save system resources. To
re-enable QoS with the previous configurations, use the mls qos command.

When QoS is disabled, ingress traffic is switched in pass-through mode,
which means packets are switched without any rewrites and are classified to
best effort without any policing. No ingress and egress policers are
configured. All CoS values for egress traffic are mapped to queue 1.

Toggling the QoS status of the switch with this command modifies
(reallocates) the sizes of the queues. During the queue size modification,
the switch is in a *halt* mode and drops packets for a short period.
Examples

This example shows how to disable flow control on all interfaces and then
enable QoS on the switch:

Switch(config)# *interface range gigabitethernet0/1 -12*

Switch(config-if)# *flowcontrol receive off*

Switch(config-if-range)# *flowcontrol send off*

Switch(config-if-range)# *exit*

Switch(config)# mls qos

This example shows how to disable all QoS processing on the switch:

Switch(config)# no mls qos

On Mon, Jul 27, 2009 at 9:23 AM, Anantha Subramanian Natarajan <
anantha.natarajan_at_gravitant.com> wrote:

> Hi Kaniyath,
>
> One thing which I understood is,I may be wrong ........When a switch wants
> to respond to flow control bits received from a router (directly connected
> to the switch port),then "mls qos" required to be disabled on a switch.
>
> Thanks
>
> Regards
> Anantha Subramanian Natarajan
>
> On Sun, Jul 26, 2009 at 12:07 AM, kaniyath minha
> <minha.kaniyath_at_gmail.com>wrote:
>
> > Dear
> >
> > where mls qos should enable and where it is not required..its confusing
> me.
> >
> > Is Police require it or not?
> >
> > please give in detail.
> >
> > thanks and regards
> >
> >
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> >
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Received on Mon Jul 27 2009 - 09:54:31 ART