VOIP is being implemented in the Company network and you need to assess the need for
QoS. Which of the following network problems would indicate a need to implement QoS
features? (Select three)
A.
Mis-routed packets
Configure qos all command under Switch CompanyB fa0/1 interface.
B.
Excess jitter
Configure mls qos trust cos command under Switch CompanyB fa0/1 interface.
C.
Delay of critical traffic
Configure mls qos trust cos 5 command under Switch CompanyB fa0/1 interface.
D.
Packet loss due to congestion
Configure qos cos 5 command under Switch CompanyB fa0/1 interface.
E.
Data link layer broadcast storms
Configure mls qos trust cos command under Switch CompanyA fa0/1 interface.
F.
FTP connections unsuccessful
If only FTP sessions were having issues, then the FTP application or FTP server should
be corrected. Normally, FTP sessions are not delay sensitive due to the re-transmission
nature of TCP and do not require QoS.
QUESTION 193
The Company network is displayed in the following topology exhibit: 
Workstation 1 traffic is set for cos 5 and the switch CompanyA sends workstation 1 traffic to
the switch CompanyB. However, not all of the traffic from Switch CompanyA is from
workstation 1.
Switch CompanyA configurations Switch CompanyB Configuration:
mls qos mls qos
interface fa0/1 interface fa0/1
switchport mode trunk switchport trunk mode
switchport trunk encapsulation dot 1q switchport trunk encapsulation dot 1q
switchport trunk native vlan 1 switchport trunk native vlan 1
Frames from Workstation 1 are given the rightful priority through Switch CompanyA, but
Switch CompanyB doesn’t reciprocate, and treats Workstation 1 frames as if they have no
precedence. Which of the following actions will prioritize traffic from Workstation 1?
Configure qos cos 5 command under Switch CompanyA fa0/1 interface.
F.
FTP connections unsuccessful
If only FTP sessions were having issues, then the FTP application or FTP server should
be corrected. Normally, FTP sessions are not delay sensitive due to the re-transmission
nature of TCP and do not require QoS.
QUESTION 193
The Company network is displayed in the following topology exhibit:
Workstation 1 traffic is set for cos 5 and the switch CompanyA sends workstation 1 traffic to
the switch CompanyB. However, not all of the traffic from Switch CompanyA is from
workstation 1.
Switch CompanyA configurations Switch CompanyB Configuration:
mls qos mls qos
interface fa0/1 interface fa0/1
switchport mode trunk switchport trunk mode
switchport trunk encapsulation dot 1q switchport trunk encapsulation dot 1q
switchport trunk native vlan 1 switchport trunk native vlan 1
Frames from Workstation 1 are given the rightful priority through Switch CompanyA, but
Switch CompanyB doesn’t reciprocate, and treats Workstation 1 frames as if they have no
precedence. Which of the following actions will prioritize traffic from Workstation 1?
Configure qos cos 5 command under Switch CompanyA fa0/1 interface.
A.
Mis-routed packets
Configure qos all command under Switch CompanyB fa0/1 interface.
B.
Excess jitter
Configure mls qos trust cos command under Switch CompanyB fa0/1 interface.
C.
Delay of critical traffic
Configure mls qos trust cos 5 command under Switch CompanyB fa0/1 interface.
D.
Packet loss due to congestion
Configure qos cos 5 command under Switch CompanyB fa0/1 interface.
E.
Data link layer broadcast storms
Configure mls qos trust cos command under Switch CompanyA fa0/1 interface.
F.
FTP connections unsuccessful
If only FTP sessions were having issues, then the FTP application or FTP server should
be corrected. Normally, FTP sessions are not delay sensitive due to the re-transmission
nature of TCP and do not require QoS.
QUESTION 193
The Company network is displayed in the following topology exhibit:
Workstation 1 traffic is set for cos 5 and the switch CompanyA sends workstation 1 traffic to
the switch CompanyB. However, not all of the traffic from Switch CompanyA is from
workstation 1.
Switch CompanyA configurations Switch CompanyB Configuration:
mls qos mls qos
interface fa0/1 interface fa0/1
switchport mode trunk switchport trunk mode
switchport trunk encapsulation dot 1q switchport trunk encapsulation dot 1q
switchport trunk native vlan 1 switchport trunk native vlan 1
Frames from Workstation 1 are given the rightful priority through Switch CompanyA, but
Switch CompanyB doesn’t reciprocate, and treats Workstation 1 frames as if they have no
precedence. Which of the following actions will prioritize traffic from Workstation 1?
Configure qos cos 5 command under Switch CompanyA fa0/1 interface.
Explanation:
Loss, jitter, and delay are the three reasons for implementing QoS features on modern
networks. Loss is when a packet disappears on a network. Jitter is a timing mismatch
between two way traffic, and delay is when a packet takes too long to get somewhere.
Incorrect Answers:
A: This would indicate a routing problem, or packets being “black-holed.” QoS would not
help in this situation.
E: Broadcast storms indicate a problem on a LAN segment, such as a babbling host, too
many hosts, a segment that is too large, a bad application, etc. QoS would not help in this
situation.The default action is for a switch with QoS features activated not to trust edge devices and
any frames that enter the switch have their CoS re-written to the lowest priority of zero. If the
edge device can be trusted, this default behaviour must be overridden and the access switch
must be configured to switch the frame, leaving the CoS bits untouched.
The trust is configured on the switch port using the command:
switch(config-if)#mls qos trust cos