From: Scott Morris (swm@emanon.com)
Date: Tue Dec 21 2004 - 01:21:42 GMT-3
Hehehehe... You are assuming that there is some easily derived logic to
this structure!!! :)
Bad, bad idea.
Anyway, what I think you'll find as you watch the history of the commands
and when each was introduced is that you'll see a progression of becoming
less sane and more anal-retentive in the meanings. Cos-to-queue makes
sense. IP-prec and DSCP to CoS makes sense. But what if you want that
"one-off" kinda thing?
Someone, somewhere, and likely with a lot of clout (translation = lots of
equipment) wanted to do something out of the ordinary.
All in all, I wouldn't stress out too much about it. Know what it is, file
it in the back of your head as semi-useful information and move on to other
important things like how the hell can they mess up my OSPF network!?!?!
HTH,
Scott
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Monday, December 20, 2004 4:31 PM
To: swm@emanon.com; 'Group Study'
Subject: Re: 3550 QoS and Switch Priority
Thanks Scott,
Those documentation writers at Cisco could learn alot from you about how to
write clearly.
Now, that it's clear what this command does, any chance you could explain
why this command is needed
given that there's another command, wrr-queue cos-map <queue #> cos# cos#
cos#, that maps cos to queues
and there's still another map that maps dscp's to cos.
Assuming a fastethernet interface, how does the 3550 determine which queue a
frame goes into?
Does it look at the internal dscp value and use the dscp to switch priority
map to directly select the queue?
Or, does it look at the cos value and decide by using the cos to queue map?
What happens when a frame has both a cos and dscp value and the two values
don't map to the same queue?
Thanks Scott. You're the best.
Tim
----- Original Message -----
From: "Scott Morris" <swm@emanon.com>
To: "'ccie2be'" <ccie2be@nyc.rr.com>; "'Group Study'"
<ccielab@groupstudy.com>
Sent: Monday, December 20, 2004 3:25 PM
Subject: RE: 3550 QoS and Switch Priority
> The switch-priority is in reference to the four hardware queues that are
> associated with each ethernet port.
>
> Look at the defaults:
>
> Table 2-9 Default DSCP-to-Switch Priority
> DSCP Value/Switch Priority
> 0-15/0
> 16-31/1
> 32-47/2
> 48-63/3
>
> DSCP values 0-15 covers IP precedence values 0 and 1, which is COS 0 and 1
> by default.
> DSCP values 16-31 covers IP precedence values 2 and 3, which is COS 2 and
3
> by default.
>
> So on and so forth.
>
> 'show mls qos interface queueing' will show the defaults.
>
> HTH,
>
>
> Scott Morris, MCSE, CCDP, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
> #4713, JNCIP, CCNA-WAN Switching, CCSP, Cable Communications Specialist,
IP
> Telephony Support Specialist, IP Telephony Design Specialist, CISSP
> CCSI #21903
> swm@emanon.com
>
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> ccie2be
> Sent: Monday, December 20, 2004 10:37 AM
> To: Group Study
> Subject: 3550 QoS and Switch Priority
>
> Hi guys,
>
> I came across an option for the above command that I can't figure out.
>
> See this link:
>
>
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12225se/3550cr/cli
> 1
> .htm#wp1862902
>
>
> This option allows you to map dscp values to switch priority.
>
> mls qos map dscp-switch-priority <dscp-list> to <switch-priority>
>
> The CR says for this option the following:
> Define the DSCP-to-switch-priority map. This map generates the priority of
a
> request to the switch fabric when using a priority-aware switch fabric.
> For dscp-list, enter up to eight DSCP values, with each value separated by
a
> space. The range is 0 to 63. Then enter the to keyword.
> For switch-priority, the range is 0 to 3.
>
> I've got some questions about this.
>
> 1) Is this actually something that can be done on 3550?
>
> 2) What does "switch-priority" mean in this context? (Notice that the
range
> of values for switch priority is only 0 to 3 which doesn't sound like this
> switch priority has anything to do with the Spanning Tree Protocol.)
>
> 3) What do they mean by "priority-aware switch fabric" and does the 3550
> have this?
>
> 4) If the 3550 has this what's the default dscp to switch-priority
mapping?
>
> I spent a couple hours already trying to find out the answers to these
> questions but the only references I've found were related to the 6500
switch
> fabric.
>
> Any help would be appreciated.
>
> TIA, Tim
>
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