Cisco GSR 12000 routers, which are commonly used as core routers, do
not support DSCP. The QoS policies are created using CoS.
On Aug 19, 2009, at 12:00 PM, Bodnar, Edward wrote:
I don’t think I am asking my question properly.
If I were setting up a network using layer 2 and layer 3 devices.
When would I use CoS and when would I use DSCP. Some of the
scenarios I am finding use DSCP from end to end. But other times
they break it up and map from DSCP to CoS then back again. Not sure
why they would do that.
Ed,
From: prakash patel [mailto:[email protected]]
Sent: Wednesday, August 19, 2009 2:55 PM
To: Bodnar, Edward; [email protected]; [email protected]
Subject: RE: [OSL | CCIE_RS] QOS question
If device is giving you DSCP and you like to change it to COS from
egress point of view.
Configuring the DSCP-to-CoS Map
You use the DSCP-to-CoS map to generate a CoS value, which is used
to select one of the four egress queues.
Table 33-14 shows the default DSCP-to-CoS map.
Table 33-14 Default DSCP-to-CoS Map
DSCP Value
CoS Value
0-7
0
8-15
1
16-23
2
24-31
3
32-39
4
40-47
5
48-55
6
56-63
7
If these values are not appropriate for your network, you need to
modify them.
Configuring the DSCP-to-CoS Map
You use the DSCP-to-CoS map to generate a CoS value, which is used
to select one of the four egress queues.
Table 33-14 shows the default DSCP-to-CoS map.
Table 33-14 Default DSCP-to-CoS Map
DSCP Value
CoS Value
0-7
0
8-15
1
16-23
2
24-31
3
32-39
4
40-47
5
48-55
6
56-63
7
If these values are not appropriate for your network, you need to
modify them.
From: [email protected]
To: [email protected]; [email protected]; [email protected]
Date: Wed, 19 Aug 2009 13:48:54 -0500
Subject: RE: [OSL | CCIE_RS] QOS question
That would lead me to believe that I can do DSCP on a switch. If
that’s the case then when would I do DSCP vs CoS?
From: desmond Black [mailto:[email protected]]
Sent: Wednesday, August 19, 2009 2:45 PM
To: Bodnar, Edward; 'prakash patel'; [email protected]
Subject: Re: [OSL | CCIE_RS] QOS question
The DSCP to DSCP mapping you refering to is actually Mutation-Map
which is done on a Trusted QOS boundary but needs change.
Example would be 2 Companies merging networks. The other company's
network has already marked the type of traffic in their own way in
DSCP but then your company has a different Policy for that traffic.
So rather than again Classifying and then marking.............you
simply use a Mutation map and do 1-to-1 mapping.
Desmond Black,
In Pursuit of CCIE!!
India
----- Original Message -----
From: "Bodnar, Edward"
To: "'prakash patel'" , "[email protected]"
Subject: Re: [OSL | CCIE_RS] QOS question
Date: Wed, 19 Aug 2009 13:15:57 -0500
So any time I pass from a layer 2 device to a layer 3 device I need
to translate the CoS to DSCP. And any time I go from a layer 3
device to layer 2 device I need to translate DSCP to CoS? If this
is true then why do that have DSCP to DSCP translations in switches ?
From: prakash patel [mailto:[email protected]]
Sent: Wednesday, August 19, 2009 2:09 PM
To: Bodnar, Edward; [email protected]
Subject: RE: [OSL | CCIE_RS] QOS question
Layer 2 devices connection ...USE COS
LAYER 3 devices use DSCP.
From: [email protected]
To: [email protected]
Date: Wed, 19 Aug 2009 13:01:01 -0500
Subject: [OSL | CCIE_RS] QOS question
When would I use CoS over DSCP or DSCP over CoS.
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