[c-nsp] ingress vs egress queues

[Aaron Riemer]

Thanks again Phil.

Cheers,

-Aaron

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Phil Mayers
Sent: Thursday, 3 March 2011 6:34 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] ingress vs egress queues

On 03/03/2011 03:30 AM, Aaron Riemer wrote:
> Hey guys,
>
>
>
> Can someone please explain to me the difference between ingress and egress
> queues on catalyst switches?

Ingress queues are more or less useless[1], since most Catalyst switches 
have non-blocking (or nearly so) fabric/interconnects.

Egress queues are useful, for all the "normal" reasons.

>
>
>
> I always thought Ingress was traffic coming 'in' to the switch port from a
> device and egress traffic coming out of the port but I don't think this is
> correct?

You were right. Ingress/Egress are from the perspective of the switch.

>
>
>
> Does a packet first go through the ingress queue and then to the egress
> queue before it is 'switched'.

Yes

>
>
>
> I have been trying to find some good documentation to aid my understanding
> in this area. If anyone could help me out with this it would be greatly
> appreciated.

The QoS SRND is useful for background info on Catalyst QoS. Other links 
have been posted to the list fairly recently - have a look at the archives.

Regards,
Phil

[1] If you believe the explanation in the QoS SRND, which I find 
reasonably convincing.
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