From: Scott Morris (swm@emanon.com)
Date: Fri Feb 27 2004 - 11:32:11 GMT-3
There are also dscp-cos maps that you can change along the way. Mutation
maps are interesting creatures to play with.
Default operation is to map IP Prec directly to COS (each have 8 possible
values). DSCP has 64 possible values, so there's a little overlap there.
64 --> 8 --> 4 queues There has to be SOME mapping going on!
Any of these commands allow you to start tweaking the default maps as well
as being able to implement a policy regarding their setup and handling.
The wrr-queue dscp-map option allows you to map particular DSCP values to
one of two discard thresholds. So it's not so much that a DSCP value can
exist in more than one place, but that you have less WRED maps than you do
queues. Think of it like applying one policy to multiple interfaces.
You're setting some values that won't exist in certain places, but it makes
the overall configuration smaller and more compact.
Check out
http://www.cisco.com/en/US/tech/tk389/tk813/technologies_tech_note09186a0080
1558cb.shtml#topic4 it has some decent discussions about the mapping.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
JNCIS, et al.
IPExpert CCIE Program Manager
IPExpert Sr. Technical Instructor
swm@emanon.com/smorris@ipexpert.net
http://www.ipexpert.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Ramasubramanian Sethuraman
Sent: Thursday, February 26, 2004 11:53 PM
To: ccielab@groupstudy.com
Cc: snrmanian@hotmail.com
Subject: cat35550 qos
I have a question regarding 3550 Qos. I read that based on the internal COS
value of the packet, one of the 4 o/p queues is selected. But the COS value
itself is based on the DSCP value of the packet after policiing, which
implies there is a one-to-one correspondence between DSCP and the selected
queue (each queue has unique set of DSCP's)
The point i don't understand is there is also a option(ingress interface) to
map dscp to either of the 2 thresholds for each o/p queue using the command
"wrr-queue dscp-map 1|2 <dscp set>". This tells that same DSCP can exist on
multiple queues which contradicts my earlier understanding that each queue
has a unique set of DSCP's.
Pls clarify if i'm missing something.
This is the sample config from CCO
Switch(config)# interface gigabitethernet0/1 <-- egress
Switch(config-if)# wrr-queue random-detect max-threshold 1 50 100
Switch(config-if)# wrr-queue random-detect max-threshold 2 70 100
Switch(config-if)# wrr-queue random-detect max-threshold 3 50 100
Switch(config-if)# wrr-queue random-detect max-threshold 4 70 100
Switch(config-if)# exit Switch(config)# interface gigabitethernet0/2 <--
ingress Switch(config-if)# mls qos trust dscp Switch(config-if)# wrr-queue
dscp-map 1 0 8 16 24 32 40 48 56 Switch(config-if)# wrr-queue dscp-map 2 10
20 30 40 50 60
explanation
---------------
As a result of this configuration, when the queues 1 and 3 are filled above
50 percent, packets with DSCPs 0, 8, 16, 24, 32, 40, 48, and 56 are randomly
dropped. The same packets are randomly dropped when queues 2 and 4 are
filled above 70 percent. When the second threshold (100 percent) is
exceeded, all queues randomly drop packets with DSCPs 10, 20, 30, 40, 50,
and 60.
thanks,
subbu
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