From: ccie2be (ccie2be@nyc.rr.com)
Date: Mon Dec 20 2004 - 18:43:12 GMT-3
PS:
In the 3550 Config Guide, in the Qos chapter, I found this comment:
"Before the traffic reaches the scheduling stage, QoS uses the configurable
DSCP-to-CoS map to derive a CoS value from the internal DSCP value. Through
the CoS-to-egress-queue map, the CoS values select one of the four egress
queues for output processing."
If the above comment is true, when would the dscp to switch-priority (really
Queue #) ever come into play?
Thanks again, 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
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Mon Jan 03 2005 - 10:31:28 GMT-3