A couple of things: 1) "auto qos voice trust" applies "mls qos trust cos" to any layer 2 interface. Therefore, it is not a good indication of what should be done in a given situation.
2) Switch to switch connections should trust DSCP based on the Enterprise QoS SRND. In particular, look at figure 2-2. This is because we should have already determined the DSCP values for flows from the end devices. If we now trust CoS, we could be changing the DSCP values that were already written in the first place. For example, if I have 2 flows, one with DSCP CS3 and one with AF31, the receiving device will see both of those values if I trust DSCP (and don't manipulate DSCP along the way.) However, if I trust CoS, both will be marked to CoS 3 outbound on the connection to the next switch. On the receiving switch, the CoS-DSCP map will determine the DSCP value, which will therefore be the same for both streams. That is not end-to-end QoS. Jason Boyers - CCIE #26024 (Wireless) Technical Instructor - IPexpert, Inc. Mailto: *[email protected] * On Thu, Jun 23, 2011 at 12:40 PM, Raul Manzano <[email protected]> wrote: > Hi Guys. > > I need your help. I'm working to build a table with the recommended > configurations for every type of interface. I know this status may change > due to lab requirements but having a "start line" can help us to speed up > the lab configuration or to recognize a lab requirement that can > change their configuration. > > As far I know, by default: > > + Layer 2: > - Access layer interface always trust DSCP. > - Trunk layer interface, hum, normaly you should trust COS but not always: > exceptions > * When on a link to a wired phone??? 7921G deployment guide told us to > trust DSCP (assuming SCCP and RTP traffic is setting correctly from the > Phone I think) , Others design guides for Cisco IP phones or, the use of > Auto QoS command, suggest the use of trust COS. > * When on a link to WLC (Trust COS by default if all vlans are tagged, if > not, do we trust DSCP??) > * When on Layer2 UPlink, always I though that we should trust COS but > yesterday I read in a lab that trust DSCP is a best practice recommendation. > I find nothing to indicate it. > * When on an Autonomous AP or H-REAP link: Coz, a sea of doubts, Autonomous > AP normaly trust COS, and we can do all the traffic to pass 802.1q tagged, > If we trust in cos markings we can trust cos on the interface because all > traffic can be tagged. If we need to use a native VLAN (traffic not tagged) > I assumed that with trust COS all the traffic not tagged is marked to COS 0 > and DSCP 0 and this is not desirable. In the same way we have the H-REAP AP, > with the difference of the native vlan that is mandatory, then we are forced > to use trust DSCP I think. > > +Layer 3: > - Layer 3 UPlink: Trust DSCP > > Careful with this, I have not taken into account the use, if the lab > requirement point to it, the use of vlan-based QoS or MQC, only to keep in > mind which are the "default" configurations for every interface if lab > requirement does not say otherwise. > > Thanks. > > Cheers!! > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > >
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
