From: amilabs (amilabs@optonline.net)
Date: Wed Jan 21 2004 - 15:29:44 GMT-3
There is a priority-queue out interface command and that is used for
packets marked with the internal dscp to be priority queued into the
fourth output queue on each interface. It kind of turns the four output
queues into the traditional router ios priority queueing. Meaning that
traffic with an internally marked or trusted dscp equaling cos/ipprec 6
or 7 to just use the priority queue over the others. The 3550 has a port
type for output queuing of 1p3q1t. Packets classified for the higher
dscp can be sent to the strict priority queue for output processing. Of
course this could lead to queue starvation and that is why there are
options to change the queue sizes and wrr. Take this into consideration
with using policers to restrict the flow and perform tail dropping etc.
A great book for Qos for all the Catalyst platforms and the 3550
especially is called:
Cisco Catalyst QoS:
Quality of Service in Campus Networks.
Cisco Press
ISBN:1-58705-120-6
It is a very good book and explains everything about dscp, mappings,
trusting, classifying, marketing, policing, congestion management and
avoidance etc much better than the docs...
Definitely worth having in your study library.
Regards..
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
D T
Sent: Wednesday, January 21, 2004 1:00 PM
To: antonio.sanchez-monge@hp.com; ccie2be@nyc.rr.com
Cc: ccielab@groupstudy.com
Subject: RE: 3550 QoS
Hi Antonio,
Actually, according to the 3550 config guide, the transmit queue used by
a
pkt depends solely on the pkt's cos - the config guide says that a few
times. However, the cos value can be determined from the ip prec
(indirectly by referring to an ip prec to dscp mapping table) or the
dscp
value directly (by referring to a dscp to cos mapping table). In either
case, no mention is made to switch priority which is what my original
question was about.
Thanks, just the same.
>From: "SANCHEZ-MONGE,ANTONIO (HP-France,ex2)"
><antonio.sanchez-monge@hp.com>
>Reply-To: "SANCHEZ-MONGE,ANTONIO (HP-France,ex2)"
><antonio.sanchez-monge@hp.com>
>To: "'ccie2be'" <ccie2be@nyc.rr.com>
>CC: ccielab@groupstudy.com
>Subject: RE: 3550 QoS
>Date: Wed, 21 Jan 2004 18:23:56 +0100
>
>Hi,
>
>I talked about IP precedence, not about CoS ;)
>
>Cheers,
>Ato.
>
>
>-----Original Message-----
>From: ccie2be [mailto:ccie2be@nyc.rr.com]
>Sent: miircoles, 21 de enero de 2004 15:24
>To: SANCHEZ-MONGE,ANTONIO (HP-France,ex2)
>Cc: ccielab@groupstudy.com
>Subject: Re: 3550 QoS
>
>
>Hey Antonio,
>
>Thanks for getting back to me.
>
>IMHO, I think you're mistaken on this one because there's a different
>command used for mapping cos to queue. That command is " wrr-queue
>cos-map <q#> <cos#, cos#...>
>
>I suppose it's possible for there to be 2 commands which do the same
>thing, but it doesn't sound right to me. Hopefully, somebody will
>clear this up.
>
>dt
>----- Original Message -----
>From: "SANCHEZ-MONGE,ANTONIO (HP-France,ex2)"
><antonio.sanchez-monge@hp.com>
>To: "'ccie2be'" <ccie2be@nyc.rr.com>
>Cc: <ccielab@groupstudy.com>
>Sent: Wednesday, January 21, 2004 3:30 AM
>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_note09186
>a0080
>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/c3550/12119ea1/3550
>cr/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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