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IP SLA Questions 2

July 11th, 2017 in ROUTE 300-101 Go to comments

Question 1

Explanation

User Datagram Protocol (UDP) Jitter for VoIP is the most common operation for networks that carry voice traffic, video, or UDP jitter-sensitive applications. Requires Cisco endpoints.

Note: The ICMP jitter operation is similar to the IP SLAs UDP jitter operation but does not require a Cisco endpoint (maybe only Cisco router has been designated to reply to Cisco IOS IP SLA test packets).

The config below shows an example of configuring UDP Jitter for VoIP:

Router(config)# ip sla 10
//Configures the operation as a jitter (codec) operation that will generate VoIP scores in addition to latency, jitter, and packet loss statistics. Notice that it requires an endpoint.
Router(config-ip-sla)# udp-jitter 209.165.200.225 16384 codec g711alaw advantage-factor 10
//The below configs are only optional
Router(config-ip-sla-jitter)# frequency 30
Router(config-ip-sla-jitter)# history hours-of-statistics-kept 4
Router(config-ip-sla-jitter)# owner admin
Router(config-ip-sla-jitter)# tag TelnetPollServer1
Router(config-ip-sla-jitter)# threshold 10000
Router(config-ip-sla-jitter)# timeout 10000
Router(config-ip-sla-jitter)# tos 160

Reference: http://www.cisco.com/en/US/technologies/tk648/tk362/tk920/technologies_qas0900aecd8017bd5a.html & http://www.cisco.com/c/en/us/td/docs/ios/ipsla/configuration/guide/15_s/sla_15_0s_book/sla_udp_jitter_voip.pdf

Question 2

Explanation

There is no problem with the Fa0/0 as the source interface as we want to check the ping from the LAN interface -> A is not correct.

Answer B is not correct as we must track the destination of the primary link, not backup link.

In this question, R1 pings R2 via its LAN Fa0/0 interface so maybe R1 (which is an ISP) will not know how to reply back as an ISP usually does not configure a route to a customer’s LAN -> C is correct.

There is no problem with the default route -> D is not correct.

For answer E, we need to understand about how timeout and threshold are defined:

Timeout (in milliseconds) sets the amount of time an IP SLAs operation waits for a response from its request packet. In other words, the timeout specifies how long the router should wait for a response to its ping before it is considered failed.Threshold (in milliseconds too) sets the upper threshold value for calculating network monitoring statistics created by an IP SLAs operation. Threshold is used to activate a response to IP SLA violation, e.g. send SNMP trap or start secondary SLA operation. In other words, the threshold value is only used to indicate over threshold events, which do not affect reachability but may be used to evaluate the proper settings for the timeout command.

For reachability tracking, if the return code is OK or OverThreshold, reachability is up; if not OK, reachability is down.

Therefore in this question, we are using “Reachability” tracking (via the command “track 10 ip sla 1 reachability”) so threshold value is not important and can be ignored -> Answer E is correct. In fact, answer E is not wrong but it is the best option left.

This tutorial can help you revise IP SLA tracking topic: http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/813-cisco-router-ipsla-basic.html and http://www.ciscozine.com/using-ip-sla-to-change-routing/

Note: Maybe some of us will wonder why there are these two commands:

R1(config)#ip route 0.0.0.0 0.0.0.0 172.20.20.2 track 10
R1(config)#no ip route 0.0.0.0 0.0.0.0 172.20.20.2

In fact the two commands:

ip route 0.0.0.0 0.0.0.0 172.20.20.2 track 10
ip route 0.0.0.0 0.0.0.0 172.20.20.2

are different. These two static routes can co-exist in the routing table. Therefore if the tracking goes down, the first command will be removed but the second one still exists and the backup path is not preferred. So we have to remove the second one.

Question 3

Explanation

A primary benefit of Cisco IOS IP SLAs is accuracy, embedded flexibility, and cost-saving, a key component of which is the Cisco IOS IP SLAs responder enabled on the target device. When the responder is enabled, it allows the target device to take two timestamps: when the packet arrives on the interface at interrupt level and again just as it leaves. This eliminates processing time. This timestamping is made with a granularity of sub-millisecond (ms). The responder timestamping is very important because all routers and switches in the industry will prioritize switching traffic destined for other locations over packets destined for its local IP address (this includes Cisco IOS IP SLAs and ping test packets). Therefore, at times of high network activity, ping tests can reveal an inaccurately large response time; conversely, timestamping on the responder allows a Cisco IOS IP SLAs test to accurately represent the response time due.

Reference: http://www.cisco.com/en/US/technologies/tk648/tk362/tk920/technologies_white_paper0900aecd8017f8c9_ps6602_Products_White_Paper.html

Note: The ICMP echo operation is used to cause ICMP echo requests to be sent to a destination to check connectivity

Question 4

Explanation

The “show ip sla statistics” command displays the current operational status and statistics of all IP SLAs operations or a specified operation so the answer “operation availability” is the best choice here.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/ipsla/command/reference/sla_book/sla_04.html

Question 5

Explanation

You can configure a tracked list of objects with a Boolean expression, a weight threshold, or a percentage threshold.

The example configures track list 1 to track by weight threshold.

Switch(config)# track 1 list threshold weight
Switch(config-track)# object 1 weight 15
Switch(config-track)# object 2 weight 20
Switch(config-track)# object 3 weight 30
Switch(config-track)# threshold weight up 30 down 10

If object 1, and object 2 are down, then track list 1 is up, because object 3 satisfies the up threshold value of up 30. But, if object 3 is down, both objects 1 and 2 must be up in order to satisfy the threshold weight.

This configuration can be useful if object 1 and object 2 represent two small bandwidth connections and object 3 represents one large bandwidth connection. The configured down 10 value means that once the tracked object is up, it will not go down until the threshold value is equal to or lower than 10, which in this example means that all connections are down.

The below example configures tracked list 2 with three objects and a specified percentages to measure the state of the list with an up threshold of 70 percent and a down threshold of 30 percent:

Switch(config)# track 2 list threshold percentage
Switch(config-track)# object 1
Switch(config-track)# object 2
Switch(config-track)# object 3
Switch(config-track)# threshold percentage up 51 down 10

This means as long as 51% or more of the objects are up, the list will be considered “up”. So in this case if two objects are up, track 2 is considered “up”.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/blades/3020/software/release/12-2_58_se/configuration/guide/3020_scg/swhsrp.pdf

Question 6

Question 7

Question 8

Question 9

Explanation

Maybe this question wants to ask “which location IP SLAs are usually used to monitor the traffic?” then the answer should be WAN edge as IP SLA is usually used to track a remote device or service (usually via ping).

Comments
  1. sallu
    August 8th, 2017

    please share me the questions for the same

  2. ali
    August 22nd, 2017

    @Anonymous which dump did you follow??

  3. Anonymous
    August 27th, 2017

    @Anonymous , are the dumpZ ( Digitaltut ) valid ?

  4. tukul
    September 23rd, 2017

    are the dump digitaltut valid? uptodate until now?

  5. cl
    September 29th, 2017

    For Q2 the answer E is not correct. The correct answer should is A,C. Normally when configuring source interface for a IP SLA we choose the directly connected interface (which ensures that it is always reachable). No ISP will have the LAN address of R1 in its routing table.

  6. mago
    October 27th, 2017

    why in q2 the threshold value is wrong?
    the formula is frequency>timeout>threshold, so the threshold 500 is right

  7. mago
    November 4th, 2017

    in Q2 the source interface is wrong, should be FastEthernet1/0

  8. Csaba
    November 8th, 2017

    Q2. The explanation says:

    “..we are using “Reachability” tracking (via the command “track 10 ip sla 1 reachability”) so threshold value is not important and can be ignored ..”

    If it can be ignored in this case, how could it be a reason for IP SLA tracking failure?

  9. 1WAY
    December 14th, 2017

    This explanation given in Q2 contradicts the answer to Q6 in the ‘IP SLA1’ section.

  10. 1WAY
    January 10th, 2018

    Ignore my previous comment, IP SLA1 Q6 refers return codes for state tracking where IP SLA2 Q2 refers to reachability tracking.

    Agree with others though that Q2 should be A,C.

  11. Anonymous
    March 13th, 2018

    Q2 C,E correct

    The threshold value must not exceed the value of the timeout parameter.

    This is the CISCO recommendation.

  12. unstoppable
    April 19th, 2018

    Anonymous,

    your explanation is good! thanks.

    (frequencyseconds ) > (timeoutmilliseconds ) > (thresholdmilliseconds)

  13. Marcus
    April 23rd, 2018

    I’m not sure about Q1. No such operation “udp-jitter for voip” itself, there is an udp-jitter which can be used for voip measurement. May be we have an incomplete question here.

  14. unstoppable
    April 28th, 2018

    sorry, the Q2, threshold value 500 is < than timeout 5000. please ignore my comment above.

  15. sieg
    May 7th, 2018

    Q2 i don’t get it, the threshold value is ok, is less than the timeout: (timeoutmilliseconds ) > (thresholdmilliseconds ) . Why E is correct?

  16. CCNP-wanna-be
    May 28th, 2018

    C) “A route back to the R1 LAN network is missing in R2” – This one is not a right answer, there is no need for a route to R1 LAN network if the source-interface will be fa1/0.

    So… if you select A (The source interface is configured incorrectly) as correct, you cannot select C.

  17. kingkong21312312
    May 30th, 2018

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  18. runner13
    August 4th, 2018

    Q2: D.The default route has “wrong: next hop IP address. the last command (ip route 0.0.0.0 0.0.0.0 172.30.30.2.5) is not on the network of secondary link 172.30.30.0/30. So this seems to me as candidate to be the an reason to have IP SLA track failure. I agree that C is also the one answer.

  19. runner13
    August 4th, 2018

    My bad on my previous answer. it is the admin distance where the 5 goes not to the ip address..sorry .

  20. yjuyii
    October 12th, 2018

    After the 28th change, the previous question bank is useless. It depends on the latest 29th, and now if you want to prepare for the exam, you must find the question bank after the 29th.
    W w w .

    cciedumps.xyz/ccie_rs.php?utm_source=bbs&utm_medium=bbs

  21. Dmitry
    October 12th, 2018

    Q2 right answers really are A and C.

    Q1 didn’t understand why right answer is A, why isn’t C? What do they mean about “Cisco endpoints” – IP-phones? Maybe servers Cisco (server is endpoint to)…

  22. Retaker
    October 15th, 2018

    Hi Concerns,
    I failed my CCNP route.
    I would like to know if I ever retake the exam, does it would have the same set of questions? Or it would have another sets of questions?
    Most of the questions are related to PPPoE and Frame Relay.

  23. MED
    November 1st, 2018

    Hi @ Digitaltut

    Question 2, in other words, asks for two different solutions to the problem of IPSLA.
    The first solution is to make a route on R2 (Here we assume that the local network of R1 is not reachable by R2 and so if we configure a static route from R2 to the LAN of R1, we can have a reachability of Fa0 / 0 from R1 to R2 and IPSLA is working normally.
    The second solution is to change the “source-interface” which allows IPSLA to work as the network between R1 and R2 are directly connected.
    I realized a LAB on GNS3 by simulating the network in question and in any case I had trouble to change the parameter “threshold”

  24. Sorlags
    November 11th, 2018

    Q2 : source interface on exibit is fa1/0 and on command line fa0/0. The source-interface is configured incorrectly.

    I think answer is A & C

    We have the same Exibit on IP SLA 1 and the interface is fa1/0

  25. RouteRider
    November 29th, 2018

    Q2
    The main rule for IP SLA icmp-echo: (frequency seconds ) > (timeout milliseconds ) > (threshold milliseconds )
    The commands which were used in the question:
    frequency in seconds –> 10 sec
    timeout in milliseconds –> 5000 msec
    threshold in milliseconds –> 500 msec
    The rule comes true…
    I think the source interface isn’t correct. Because fa1/0 is in front of 172.20.20.2, not Fa0/0.
    Am I right?

  26. Dany1
    December 7th, 2018

    Q2 raise a lot of debates about rule (frequency > timeout >thresold) and about answers, what are correct ones??? MED put the configuration in GNS3 (good idea) and observe some problems with threshold ( he don t specify what are problems?). But al this avalanche of comments coming from way of thinking. Even my self enter in that circle, until read MED comment. So, i put the configuration in GNS3 and is work PERFECT. That formula ( frequency > timeout > threshold) is for best practice in some cases (udp jitter. i don t rember).
    The only formula i saw on router is that:
    “R1(config-ip-sla-echo)#frequency 1
    %Error: frequency is less than timeout 5000 ms”
    and is normal because timeout is when the connection is dead and must be before another sending another SLA packet.
    So, everything is OK, what is the point of the question 2?
    Let s take one by one
    A. The source-interface is configured incorrectly
    If i configure incorrect source-interface (another IP CLASS, different from route static from R2, shut on interface, or no ip address), result is clear at show track command
    “19: %TRACKING-5-STATE: 10 ip sla 1 reachability Up->Down” – IP SLA tracking failure-
    B. change ip address destination and nothing is happening IF R3 has a static route to R1 LAN
    C. IF static route toward R1 LAN is missing, is obviously IP SLA tracking failure
    D. Is obviously false
    E. threshold value is wrong you can change a value of your desired, but IL SLA tracking is working even with threshod=timeout=500
    Correct Answers are A and C or at least in that way i thinking, a litte bit out of the box.

  27. Dany1
    December 7th, 2018

    Q1 answer is A. Good observation from Dmitry. Cisco EndPoint means VOIP application software or equipments. And the only way to measure performance is using UDP jitter for VoIP
    take into account the fact that both of them, UDP Jitter and UDP Jitter for VoIP use IP SLA Responder, difference being codec parameter used in second command.
    That is the reason for choosing A, it can use codec, like in example:
    udp-jitter 209.165.200.225 16384 codec g711alaw advantage-factor 10

  28. Dany1
    December 7th, 2018

    Digitaltut give us an example for threshold percentage:
    Switch(config)# track 2 list threshold percentage
    Switch(config-track)# object 1
    Switch(config-track)# object 2
    Switch(config-track)# object 3
    Switch(config-track)# threshold percentage up 51 down 10
    is OK, but cannot be two object with the same number (track 2 and object 2 inside track 2)
    Correct is track 4
    Error is “Router(config-track)#object 2
    % Track list cannot contain itself

  29. Meto
    December 16th, 2018

    Guys by process of elimination in question 2 , you are left with C and E .
    The source interface is not wrong , why is wrong can some one prove that is wrong using fa0/0.
    You are testing connectivity from your LAN to 172.20.20.2 . You can place also interface 1/0 as source it will still not be wrong . with source fa0/0 you are testing the full path . I have the exam on 24 December i will really like to have an explanation from digitaltut about answer E , if i dont get it i will hope that i will not get this qestion on the exam :(

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