CCNP switch slides 17 Flashcards
source
http://www.coursehero.com/flashcards/430780/CCNP-SWITCH-642-813-Voice-and-Video/
What command will automatically trust QoS information received on a trunk?
mls qos trust cos.
How many ports on a Cisco IP phone’s internal switch?
3! Upload, PC, and phone!
Layer 2 devices can only utilize what one of the three basic QoS methods?
Best Effort Delivery.
When using the command “show inline power” a class of ‘n/a’ means what?
That the switch is providing power with ILP, and NOT 802.3af.
What is Differentiated Services Delivery?
Applying QoS on a per-flow and per-hop basis for all packets.
How does Cisco ILP detect if a device needs power?
The switch sends a tone along the line, and since Cisco IP Phones auto-loopback their interfaces when powered off, the switch will ‘hear’ the tone when it is sent back.
How much DC power is applied when using PoE?
48V DC
What is Integrated Services Delivery?
Establishing a dedicated path through the network before any data is sent. Think of this as circuit switching over a packet switched network.
How many classes of power are there in 802.3af? What is the default?
5 classes (0-4), default is 0 (15.4W)
When using dot1p to trunk a Cisco IP Phone, what VLAN is voice data sent on?
VLAN 0
What are the tree types of Auto-QoS options for voice?
Cisco-phone, Cisco-softphone, and trust (used for trunks/uplinks!)
Using the ‘mls qos trust’ command what are the tree things that can be trusted? what is generally used on IP phones?
cos, ip-precedence, or DSCP. cos is used for IP Phones.
If a port is not trusted in QoS, what happens to the voice packet QoS when they hit the switch?
They are overwritten by the switch! (bad!)
How does the command ‘mls qos’ affect the way a switch trusts QoS markers?
Without it, the switch trusts everything. With it, the switch trusts NOTHING!
Typically, when should an organization trust QoS parameters, and when should it NOT?
Trust when it is generated within your own network, and do NOT trust at the boundary with any external organization.
What is the best way that a switch can detect power requirements to a phone when running ILP?
By exchanging CDP information.
At what layer should Auto-QoS be used?
the access layer, or wherever you have more QoS leveraging services (like IP phones!)
What is a QoS trust boundary?
The perimeter formed by switches that do NOT trust incoming QoS.
What does ‘power inline never’ do?
Disables PoE on that port.
How many bits are used to classify layer 3 traffic when using ToS, and how many when using DSCP?
-ToS=3bits-DSCP=6bits
What pins get the power in PoE?
Both methods send power over pairs 2 and 3 (pins 1,2 and 3,6) but 802.3af can also send on the other pairs (pins 4,5 and 7,8)
What are the four trunking methods with a Cisco IP Phone?
VLAN-configured, dot1p, untagged, none.
What are the three levels of Drop Precedence in DSCP? Which one gives better service?
Low, Medium, High. Lower is better.
