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<http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_25_see/configuration/guide/swqos.html#wp1316581> 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<http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_25_see/configuration/guide/swqos.html#wp1316581> 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.<http://www.windowslive.com/Desktop/PhotoGallery> _______________________________________________ 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<http://www.mail.com/>! ________________________________ Windows Live: Keep your friends up to date with what you do online. Find out more.<http://windowslive.com/Campaign/SocialNetworking?ocid=PID23285::T:WLMTAGL:ON:WL:en-US:SI_SB_online:082009>
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