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You are in the CCIE R&S Lab Exam, and you read the following:
8.0 Quality of Service (QoS)
8.1 Configure SW1, and its port Fa0/12, so that it is optimized for VoIP traffic if that traffic is sent from a genuine Cisco IP Phone. Use the minimal number of commands in your configuration.
2 pts
Remember the song from the 1990’s by C+C and the Music Factory entitled “Things That Make You Go Hmmmmm”? You might be having one of those moments now. We need to optimize the switch and the port for this VoIP traffic, and we only get two measly points!?!?
Well, the answer is held in the last part of the task. “Use the minimal number of commands in your configuration.” This is why we only get two points. It turns out that we really do not have to do much thanks to the rather miraculous AutoQoS feature.
AutoQoS permits the automation of QoS settings for the interface in question and the switch itself. All of this can be accomplished with an absolute minimum of configuration required from the switch administrator. For the Cisco Catalyst switches, AutoQoS automates the classification and congestion management configurations required in VoIP environments.
AutoQoS is carried out on a Catalyst switch thanks to an interface level command. The command (on a 3560) is as follows:
auto qos voip [cisco-phone | cisco-softphone | trust]
Notice the optional keywords. These keywords permit you to specify what packets will be trusted as far as QoS markings are concerned. In our example here, we need to ensure we only trust markings coming from a genuine Cisco IP Phone, so we need the cisco-phone keyword. How does our switch know the packets are coming from a genuine Cisco VoIP end user device? Well, Cisco Discovery Protocol (CDP) is relied upon for this determination.
Note that the cisco-softphone keyword enacts trust for voice packets sent from a Cisco phone running in software on a PC. Finally, the trust keyword trusts markings for VoIP packets coming from another switch or router.
Should you want to see what this feature did to your device and your port (and I would think that you want to), you can issue the show auto qos command.
And, oh yes, for those of you looking for nostalgia, here is a link to Things That Make You Go Hmmmmm.
Anthony Sequeira CCIE, CCSI
Twitter: @compsolv
Facebook: http://www.facebook.com/compsolv
Tags: CCIE R&S, CCIE R&S 4.0, CCIE Routing & Switching, Cisco
