DSCP has 63 values.so one to one mapping to COS is not possible. Some values
will be overlapped.
>From egress point of view, how the EF queue treats inside the layer 2 switch.
If you think on followings:
What type of marking you received from end host ? Whether the receiver is
switch or router ?
Do you trust DSCP ? In case of switch, do you like to change it to COS or
leave it to default ? On what priority que relies on ?
You have to think at both ends (ingress and egress port).
Remember also , there does not exist any loop or cycle between DSCP to cos and
cos to dscp or cos to cos or dscp to dscp.
I like router reads DSCP.
From: [email protected]
To: [email protected]; [email protected]; [email protected]
Date: Wed, 19 Aug 2009 14:00:49 -0500
Subject: RE: [OSL | CCIE_RS] QOS question
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.
With Windows Live, you can organize, edit, and share your photos. Click here.
_______________________________________________
For more information regarding industry leading CCIE Lab training,
please visit www.ipexpert.com
--
Be Yourself @ mail.com
Choose From 200+ Email Addresses
Get a Free Account at www.mail.com!
Windows Live: Keep your friends up to date with what you do online. Find out
more.
_________________________________________________________________
Windows Live: Keep your friends up to date with what you do online.
http://windowslive.com/Campaign/SocialNetworking?ocid=PID23285::T:WLMTAGL:ON:WL:en-US:SI_SB_online:082009
_______________________________________________
For more information regarding industry leading CCIE Lab training, please visit
www.ipexpert.com
