For a catalyst switch to offer PoE to a device, what must occur?
C.
Which one of these commands can enable PoE to a switch interface?
A.
What does a Cisdo IP phone contain to allow it to pass both voice and data packets?
C.
3 links total - PC (data), Internal to phone (VOIP), and link to the switch.
How can voice traffic be kept separate from any other data traffic theough an IP Phone?
B.
What cmd configures an IP phone to use VLAN 9 for voice traffic?
A.
What is the default voice VLAN confition for a switch port?
D.
If the following interface config cmds have been used, what VLAN numbers will the voice and data be carried over respectfully?
int gi 1/0/1
switchport access vlan 10
switchport trunk native vlan 20
switchport voice vlan 50
switchport mode access
A.
What command can verify the voice VLAN used by a Cisco IP phone?
B.
When a PC is connected to the PC switch port on an IP phone, how is QoS trust handled?
A.
An IP phone should mark all incoming traffic from an attached PC to have CoS 1. Complete the following switch command to make that happen:
switchport priority extend ____
D.
What command can verify the PoE status of each switch port?
B.
Which DSCP codepoint name usually is used for time-critical packets containing voice data?
B.
What are the 5 power classes for IEEE 802.af standards?
class maxpwr @ 48DC
0 15.4 W
1 4.0 W
2 7.0 W
3 15.4 W
4 up to 50 W (802.3at)
What are the commands to configure PoE?
G int fa 0/1
I power inline auto (or)
I power inline auto max <milliwatts> (or)
I power inline static (or)
I power inline static max <milliwatts> (or)
I power inline never
verify with:
show power inline
show power inline fa 0/1
What are the 4 ways that voice traffic can be sent to the switch?
1. vlan-id, separate vlan (vlan-id), pc data is untagged (native vlan), Trunk 802.1Q -- CoS 802.1p
2. dot1p, voice vlan is vlan 0, pc data is untagged (native vlan), Trunk 802.1Q -- CoS 802.1p
3. untagged, voice and pc data both use native vlan (untagged), Trunk 802.1Q -- CoS 802.1p
4. none, voice and pc data both use native vlan (untagged), no CoS (default mode)
verify with:
show interface switchport
show interface fa 0/1 switchport
show spanning-tree int fa 0/1
What are the 3 basic degradations to voice traffic?
Delay - aka latency
Jitter - variations in the amount of delay
Loss - loss of packets in transit
what are the 3 basic types of QoS?
Best-effort delivery
Integrated services model (intserv)
Differentiated services model (diffserv)
describe best effort QoS.
no real QoS, just the routers and switches doing their job passing data. No head of the line.
Describe intserv QoS.
uses a pre-arranged path using RSVP (Resource Reservation Protocol).
note: does not scale well for large networks. Path reservations can quickly overwhelm available bandwidth.
Describe diffserve QoS.
Applies QoS to each packet on a per hop basis.
this is a distributed model where each switch and router handles packets according to their configuration.
describe layer 2 QoS.
Layer 2 is basically not QoS capable, but, trunking adds a vlan tag, which also has a Class Of Service (CoS) field.
When the trunked packet is unencapsulated, the CoS marking is lost.
describe the 2 trunking encapsulations and how they handle COS.
IEE 8025.1Q - User field contains 3 802.1p bits for CoS. 0-7 (0=low). Native vlans are not encaped so no COS available.
Inter-Switch Link (ISL) - 4 bit user filed. lower 3 bits are for CoS. Catalyst switches can put 802.1Q CoS values into ISL seamlessly.
Layer 3 QoS with DSCP. Difference between TOS and QOS.
ToS - type of service. 3 bits. aka IP Prec.
QoS - Quality of service. 6 bits. DSCP.
DSCP Differentiated Services Code Point
Describe DSCP to IP Prec class names.
class 0 default class, best effort.
classes 1-4 Assured Forwarding, Higher AF numbers = higher pri. eachclass is sub-divided into 1-low, 2-med and 3-high. (example AF21 = Assured Forwarding class 2, medium)
Class 5 - Express forwarding. For time critical data like VoIP.
Classes 6-7 - internetwork control and network control. Routing overhead, STP, etc.
Define a trust boundary.
a perimeter formed by switches that do not trust QoS. usually at the access-layer switches.
the trust boundary allows switches to blindly trust QoS markings if they are inside the boundary.
PCs are usually untrusted.
IP phones can be trusted, but not the PC attached to them.
By letting the IP phone inside the fence, the switch has less processing to do, it just passes on to the next switch the trusted (QoS marked) packet.
Describe cmds to enable QoS on the switch for IP phones.
G mls qos
G int fa 0/1
I mls qos trust {qos | ip-prec | dscp}
I mls qos trust device cisco-phone
I switchport pri extend {cos <value> | trust}
note: cos value - ip phone would overwrite cos number in packet from pc to 0. trust parameter would allow pc to mark cos packets and the IP phone would not change it.
What cmd would configure an uplink port to be trusted, as long as they are inside the QoS fence?
G int fa 0/1
I mls qos trust cos
Detail cmds that allow auto QoS.
G int fa 0/1
I auto qos voip {cisco-phone | cisco=softphone | trust}
note, this is a macro that runs many lines of cmds. use "debug auto qos" to watch
