From: Ramasubramanian Sethuraman (snrmanian@hotmail.com)
Date: Fri Feb 27 2004 - 12:35:10 GMT-3
a typo in my earlier mail,
>From: "Ramasubramanian Sethuraman" <snrmanian@hotmail.com>
>Reply-To: "Ramasubramanian Sethuraman" <snrmanian@hotmail.com>
>To: swm@emanon.com, ccielab@groupstudy.com
>Subject: RE: cat35550 qos
>Date: Fri, 27 Feb 2004 15:28:52 +0000
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>Scott,
>
>Thanks for the reply.
>
>I also read dscp-to-cos and i was understanding like this
>
>case a ) trust dscp (or) use dscp-dscp mutation at the i/p interface that
> results in foll flow for a packet inside 3550
>
> dscp --- dscp --- policed dscp --- cos --- o/p queue selected
>
>case b ) trust precedence (or) use ip-precedence-dscp map at the i/p
>interface
>
> prec --- dscp --- policed dscp --- cos --- o/p queue selected
>
>case c ) trust cos (or) use cos-dscp map at i/p interface
>
>cos --- dscp -- policed dscp -- cos --- o/p queue selected
>
>
>In all above cases, 64 possible dscp's at the end of policing (if its
>configured)
>will be mapped to one of 8 possible cos values. Even though multiple dscp's
>can be
>mapped to same COS, one dscp(for eg dscp 8) can be mapped to more than one
>COS.
pls read it as,
Even though multiple dscp's can be mapped to same COS, one dscp(for eg dscp
8)
will be mapped to only one COS.
thanks,
subbu
>In such a case, each dscp will be present in only queue.
>
>Pls clarify if my above understanding is right.
>
>So i was confused when i saw the statment
>
>>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.
>
>The above implies that packets with same DSCP can be spread across the 4
>queues
>and depending upon the threshold for each queue, these packets will be
>random dropped.
>For eg) packets with dscp 8 will be randomly dropped from queue 1 and 3
>if their queues are above 50 percent and similarly packets with dscp 8 wil
>be randomly
>dropped from queues 2 and 4 if the queue is above 70 percent.
>
>Pls clarify.
>
>
>thanks,
>Subbu
>
>
>
>
>
>>From: "Scott Morris" <swm@emanon.com>
>>To: "'Ramasubramanian Sethuraman'"
>><snrmanian@hotmail.com>,<ccielab@groupstudy.com>
>>Subject: RE: cat35550 qos
>>Date: Fri, 27 Feb 2004 09:32:11 -0500
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>>
>>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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