yu

QoS Questions


Here you will find answers to QoS Questions
Question 1
Which of these is a valid differentiated services PHB?
A. Guaranteed PHB
B. Class-Selector PHB
C. Reserved Forwarding PHB
D. Discard Eligible PHB
E. Priority PHB

Answer: B
Question 2
Refer to the exhibit. When applying this hierarchical policy map on the on the tunned interface, you measure high jitter for traffic going through class 1234. What is the most likely cause of this jitter?
class-map match-all 1234
  match ip precedence 5
class-map match-all 5555
  match access-group 105
class-map match-all 5554
  match access-group 104

policy-map tun-shap
 class class-default
   shape average 150000 300000
   service-policy mark

policy-map mark
 class 1234
  priority 64
 class 5555
  set dscp af31
  bandwidth remaining percent 50
  random-detect  dscp-based
 class 5554
  set dscp af32
  bandwidth remaining percent 25
  random-detect dscp-based
interface Tunnel 1
 ip address 20.2.2.1  255.255.255.252
 ip load-sharing per-packet
 load-interval 30
 qos pre-classify
 tunnel source 4.4.4.1
 tunnel destination 4.4.4.2
 service-policy output tun-shap

access-list 104 permit ip any host  5.5.5.4
access-list 105 permit ip any host 5.5.5.5
A. The configuration of a hierarchical policy map on a tunnel interface is not supported.
B. Class 5555 and class 5554 are both taking up 100% of the bandwidth, leaving nothing for class 1234.
C. The burst size for the traffic shaping is wrongly configured to 15000; this would require an interface capable of sending at 150Mb/s.
D. The burst size for the traffic shaping has been wrongly configured; it should be set as low as possible.
E. The burst size for the traffic shaping has been wrongly configured; it should be set as high as possible.

Answer: D
Question 3
Refer to the exhibit. When applying this policy map on the tunnel1 interface, you see packet loss for the TCP class starting at around 100000 b/s, instead of the configured 150000 b/s. What is the most likely cause of the discrepancy?
class-map match-any tcp
 match protocol http
 match protocol ftp
class-map match-all acl180
 match access-group 180

policy-map police
 class tcp
    police 150000 1000 conform-action transmit exceed-action drop
 class acl180
    police 150000 conform-action set-prec-transmit 2 exceed-action set-prec-transmit 1 violate-action set-prec-transmit 0

interface Tunnel1
 ip address 20.1.1.2 255.255.255.252
 service-policy input police
 load-interval 30
 tunnel-source 4.4.4.2
 tunnel destination 4.4.4.1
A. The violate-action command should not be configured.
B. The current configuration of the load-interval command on the tunnel interface is preventing proper policing calculations.
C. The burst size is too low.
D. Policing on tunnel interfaces is not supported.
E. The CIR keyword is missing in the policer.

Answer: C
Question 4
Refer to the exhibit. As a network administrator, you have configured a dual-rate, dual- bucket policer in accordance with RFC 2698 on the serial interface of you router, connecting to your provider. The SLA with your provider states that you should only send AF31 (limited to 150 kb/s), AF32 (limited to 50 kb/s)and AF33 (best effort). Your service provider claims you are not conforming to the SLA Which two things are wrong with this configuration? (Choose two.)
class-map match-all af31
 match dscp af31
class-map match-all af32
 match dscp af32
class-map match-all af33
 match dscp af33

policy-map marking
 class af31
  set dscp af31
 class af32
  set dscp af32
 class af33
  set dscp af33

policy-map limit
 class af33
  police cir 150000 bc 50000 pir 200000 be 50000
   conform-action set-dscp-transmit af31
   exceed-action set-dscp-transmit af32
   violate-action set-dscp-transmit default
 class class-default
 bandwidth 300

interface Ethernet0/1
 ip address 3.3.3.1 255.255.255.0
 no ip proxy-arp
 load-interval 30
 half-duplex
 no keepalive
 no cdp enable
 service-policy input marking

interface serial0/0
 ip address 4.4.4.1 255.255.255.252
 ip load-sharing per-packet
 encapsulation ppp
 load-interval 30
 no dce-terminal-timing-enable
 service-policy output limit
A. The configuration of a service policy on half-duplex Ethernet interfaces is not supported.
B. The class class-default sub-command of the policy-map limit command should be set to the DSCP default.
C. The violate action is wrong.
D. This policer configuration is not implementing RFC 2698 dual-bucket, dual-rate.
E. The policer is configured in the wrong class

Answer: C E
Question 5
Refer to the exhibit. You have noticed that several users in the network are consuming a great deal of bandwidth for the peer-to-peer application Kazaa2. You would like to limit this traffic, and at the same time provide a guaranteed 100 kb/s bandwidth for one of your servers. After applying the configuration in the exhibit, you notice no change in the bandwidth utilization on the serial link; it is still heavily oversubscribing the interface.
What is the cause of this problem?
no ip cef
class-map match-all kazza2
 match protocol kazza2
 class-map match-all server
 match access-group 105

policy-map p2p
 class kazaa2
 drop
 class server
 bandwidth 100
 class class-default

fair-queue

interface Serial0/0
 bandwidth 1234
 ip address 20.1.34.1 255.255.255.252
 ip load-sharing per-packet
 encapsulation ppp
 load-interval 30
 no dce-terminal-timing-enable
 service-policy output p2p 
A. CEF needs to be enabled for NBAR.
B. In class Kazaa2, you should configure a policer instead of a drop command.
C. The server class should have a priority of 100. 
D. The bandwidth parameter on serial 0/0 is wrong.
E. Kazaa2 is not a valid protocol.

Answer: A
Question 6
All of these are fundamental building blocks of a differentiated senvices Traffic Conditioner Block except which one?
A. dropper
B. classifier
C. marker
D. querier
E. meter
F. shaper

Answer: D
Question 7
Refer to the exhibit. You would like to guarantee 7 Mb/s for FTP traffic in your LAN, as it seems that peer-to-peer traffic is taking up a large amount of bandwidth. When testing the configuration, you notice that FTP traffic doesn’t reach 7 Mb/s. What is the problem?
ip cef  

class-map match-all ftp
 match protocol ftp
class-map match-all voice
 match precedence 5  

policy-map mark
 class voice
 priority 200
class ftp
 set dscp af32
 bandwidth 7000
 random-detect
 dscp-based
class class-default  

interface Tunnel1
 ip address 20.1.1.1 255.255.255.252
 load-interval 30
 qos pre-classify
 tunnel source 4.4.4.1
 tunnel destination 4.4.4.2
!
interface Tunnel2
 ip address 20.2.2.1 255.255.255.252
 load-interval 30
 qos pre-classify
 tunnel source 4.4.4.1
 tunnel destination 4.4.4.2  

interface Ethernet0/1
 ip address 4.4.4.1 255.255.255.0
 no ip proxy-arp
 load-interval 30
 half-duplex
 no keepalive
 no cdp enable
 service-policy output mark 
A. The Ethernet interface should have keepalives enabled.
B. The duplex settings are wrong on the Ethernet interface.
C. The qos pre-classify command should be removed from the tunnel interfaces.
D. the priority queue for the voice class is probably taking all the bandwidth
E. there are probably not enough interface buffers; they should be tuned.

Answer: B
Question 8
NBAR supports all of these with the exception of which one?
A. HTTP
B. IP multicast
C. TCP flows with dynamically assigned port numbers
D. non-UDP protocols

Answer: B
Explanation
NBAR classifies packets that are normally difficult to classify. For instance, some applications use dynamic port numbers. NBAR can look past the UDP and TCP header, and refer to the host name, URL, or MIME type in HTTP requests.
Question 9
Modified deficit round robin supports which of these functionalities?
A. priority queue
B. weighted fair queues
C. round-robin service of output queues
D. LLQ

Answer: A C
Question 10
A router is connected to an HDLC circuit via a T1 physical interface. The SLA for this link only allows for a sustained rate of 768 kb/s. Bursts are allowed for up to 30 seconds at up to line rate, with a window Tc of 125 ms.
What should the Be and Be setting be when using generic traffic shaping?
A. Be = 46320000 , Bc = 96000
B. Be = 768000 Bc = 32000
C. Be = 128000 Bc = 7680
D. Be = 0 Bc = 96000

Answer: A
Explanation
(Notice that the sustained rate is the CIR = 768kb/s)
From the formula Tc=Bc/CIR => Bc = Tc * CIR = 125ms * 768kb/s = 96000 bits
(In fact you should calculate with the default units, that is 0.125s * 768000b/s)
The T1 speed is 1.544 Mbps = 1544000bps. “Bursts are allowed for up to 30 seconds at up to line rate” ->Be = 1544000bps * 30 = 46320000 bits.
Terminologies: The term CIR refers to the traffic rate for a VC based on a business contract.
Tc
 is a static time interval, set by the shaper. 
Committed burst
 (Bc) is the number of bits that can be sent in each Tc. 
Be
 is the excess burst size, in bits. This is the number of bits beyond Bc that can be sent after a period of inactivity.
Question 11
Which two of these parameters are used to determine a forwarding equivalence class? (Choose two)
A. IP prefix
B. Layer 2 circuit
C. RSVP request from CE for bandwidth reservation
D. BGP MED value

Answer: A B
Previous
Next Post »