From: Nigel.Johnson@barclayscapital.com
Date: Wed Jan 21 2004 - 11:02:35 GMT-3
As I understand it, the 'switch priority' you mention is referring to the
internal priority the switch gives to a certain packet as it is processed
internally. i.e. How important is the packet as it 'travels through the
switch'.
This document is quite detailed and I'm still working through it myself.
http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration
_guide_chapter09186a008014f36e.html
-----Original Message-----
From: SANCHEZ-MONGE,ANTONIO (HP-France,ex2)
[mailto:antonio.sanchez-monge@hp.com]
Sent: 21 January 2004 08:31
To: 'ccie2be'
Cc: ccielab@groupstudy.com
Subject: RE: 3550 QoS
Morning guys,
IMHO this map corresponds to Weighted Round Robin (WRR) which assigns
packets to 4 egress queues depending on IP precedence. In fact
"DSCP-to-switch priority" name is confusing, since the 3 last bits of DSCP
are ignored, only IP precedence is taken into account. Basically,
precedences are distributed in groups of 2 (0-1, 2-3, 4-5, 6-7), and the
corresponding packets are assigned to weighted queues (round-robin algorithm
giving preference to highest precedence queues). More details in:
http://www.cisco.com/en/US/tech/tk389/tk813/technologies_tech_note09186a0080
1558cb.shtml#topic4
I hope this helps,
Ato.
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: miircoles, 21 de enero de 2004 5:48
To: Snow, Tim
Cc: ccielab@groupstudy.com
Subject: Re: 3550 QoS
No problem. Maybe there's someone on Group Study who understands this
better and is willing to jump in. I posted that question because I read the
same thing in the command reference but didn't know what to make of it. I
recall something that sounded similar when I was learning about the Cat 5k
series but I don't even recall ever seeing anything that says whether or
not the 3550 is a priority aware switch or has a switch fabric.
dt
----- Original Message -----
From: "Snow, Tim" <timothy.snow@eds.com>
To: "'ccie2be'" <ccie2be@nyc.rr.com>
Cc: <ccielab@groupstudy.com>
Sent: Tuesday, January 20, 2004 11:35 PM
Subject: RE: 3550 QoS
> Dscp to switch priority map. It is used to signal a priority aware
> switch fabric.
>
> The default DSCP-to-switch-priority map maps DSCPs 0 to 15 to priority
> 0, DSCPs 16 to 31 to priority 1, DSCPs 32 to 47 to priority 2, and
> DSCPs 48 to 63 to priority
3.
>
> Dscp-switch priority map:
> d1 : d2 0 1 2 3 4 5 6 7 8 9
> ---------------------------------------
> 0 : 00 00 00 00 00 00 00 00 00 00
> 1 : 00 00 00 00 00 00 01 01 01 01
> 2 : 01 01 01 01 01 01 01 01 01 01
> 3 : 01 01 02 02 02 02 02 02 02 02
> 4 : 02 02 02 02 02 02 02 02 03 03
> 5 : 03 03 03 03 03 03 03 03 03 03
> 6 : 03 03 03 03
>
>
> I wish I had a better explanation for you, but I don't.
>
> T
> #12042
>
> -----Original Message-----
> From: ccie2be [mailto:ccie2be@nyc.rr.com]
> Sent: Tuesday, January 20, 2004 10:59 PM
> To: Snow, Tim
> Cc: ccielab@groupstudy.com
> Subject: Re: 3550 QoS
>
>
> Thanks Tim for getting back to me.
>
> I have to admit though, I don't understand your answer. What does cos
have
> to do with "switch priority" and what does "switch priority" have to
> do
with
> the cos to dscp map? I'm sorry if I'm a bit thick skulled but I'm
> still hoping you can explain this to me in a way I can understand.
>
> If you see from the map table below, "switch priority" has 4 possible
> values: 0, 1, 2, and 3. What do these values mean? And, under what
> circumstances should I want or need to change them? And, if I'm going
> to change them, what should I change them to?
>
> Thanks in advance
>
> ----- Original Message -----
> From: "Snow, Tim" <timothy.snow@eds.com>
> To: "'ccie2be'" <ccie2be@nyc.rr.com>
> Cc: <ccielab@groupstudy.com>
> Sent: Tuesday, January 20, 2004 10:38 PM
> Subject: RE: 3550 QoS
>
>
> > The values are used internally when the switch maps cos to dscp for
> queueing
> > purposes.
> >
> > T
> > #12042
> >
> > -----Original Message-----
> > From: ccie2be [mailto:ccie2be@nyc.rr.com]
> > Sent: Tuesday, January 20, 2004 7:13 PM
> > To: Group Study
> > Subject: 3550 QoS
> >
> >
> > Hi,
> >
> > If you do a "show mls qos map", one of the tables you'll find
> > according
> to
> > the 3550 command reference is the DSCP-to-Switch Priority and it
> > looks
> like
> > this:
> >
> > Dscp-switch priority map:
> > d1 : d2 0 1 2 3 4 5 6 7 8 9
> > ---------------------------------------
> > 0 : 00 00 00 00 00 00 00 00 00 00
> > 1 : 00 00 00 00 00 00 01 01 01 01
> > 2 : 01 01 01 01 01 01 01 01 01 01
> > 3 : 01 01 02 02 02 02 02 02 02 02
> > 4 : 02 02 02 02 02 02 02 02 03 03
> > 5 : 03 03 03 03 03 03 03 03 03 03
> > 6 : 03 03 03 03
> >
> > See the following link:
> >
> >
>
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12119ea1/3550cr/cl
> > i
> > 2.htm#2418454
> >
> > It seems to me that this Switch Priority has nothing to do with
> > Spanning Tree (true?). I tried finding out what they mean by
> > "Switch Priority",
> but
> > didn't come up with anything. Can anybody tell me what "Switch
> > Priority"
> is
> > and where I can find additional info on it?
> >
> > Thanks in advance, dt
> >
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