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VRRP Questions

November 15th, 2018 in SWITCH 300-115 Go to comments

Quick VRRP overview:

+ is IETF RFC 3768 standard
+ supports maximum 255 groups
+ 1 active and some backups
+ Use multicast address 224.0.0.18
+ Tracking via objects
+ 1 sec hello timer, 3 sec hold time
+ Authentication: plaintext or MD5 authentication
+ Preemption is enabled by default
+ Virtual IP address can be the same as physical IP address (which is running VRRP)

Question 1

Explanation

Unlike HSRP or GLBP, VRPP is an open standard.

Question 2

Explanation

In VRRP, the active router is referred to as the master virtual router.

Question 3

Question 4

Question 5

Question 6

Question 7

Explanation

From the output we learn that the current priority of the local device is 105 (via the “Priority is 105” line). But we need to notice that the tracking state is “Down” and the decrement is 15 (via the next line “Track object 1 state Down decrement 15”) so 105 is the priority after being deducted. Therefore the configured VRRP priority should be 105 + 15 = 120.

At the last line we see “Master Down interval is 3.531 sec”. We know that there is a common rule in which the backup devices should wait for three missed polls/keepalives before declaring something “down”. It is also true for VRRP but in fact VRRP adds an additional delay called “Skew time”. Therefore the default master down time is 3 x advertisement interval time + skew time (Down time = 3 x advertisement time + skew time). The Down time is 3.531 sec while the Advertisement time is 1.000 sec as shown in the output. So we can deduce the Skew time should be 0.531 sec (3.531 sec Down time = 3 x 1.000 sec Advertisement time + 0.531 sec Skew time).

Cisco uses this formula to calculate the Skew time: Skew time = (256-priority)/256

So you may ask “Why do we need the Skew time?”

Well, as we know only the Master sends hellos so when the Master goes offline all other devices in the VRRP group assume the master role simultaneously which causes some instability in the meantime. Therefore each device should wait for an additional time based on its priority, and it is the main role of Skew time.

Question 8

Explanation

VRRP has three authentication schemes:
+ No authentication
+ Plain text authentication
+ MD5 authentication

Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/12-4/fhp-12-4-book/fhp-vrrp.html

Question 9

Explanation

A VRRP router can use the same IP address of the physical interface (which is running that instance of VRRP) as the virtual IP address for the group so D is correct.

VRRP supports plaintext and MD5 authentications -> C is not correct.

Answer A is correct too, an example of configuring authentication is shown below:

Router(config)# interface Ethernet0/1
Router(config-if)# vrrp 1 ip 10.21.0.10
Router(config-if)# vrrp 1 priority 110
Router(config-if)# vrrp 1 authentication md5 key-string myVRRPKey timeout 30

So this question is a bit unclear about the number of correct answers. But answer A is not a distinguised feature of VRRP so we don’t choose it here.

Question 10

Question 11

Question 12

Explanation

To minimize network traffic, only the Master for each virtual router sends periodic VRRP Advertisement messages. A Backup router will not attempt to preempt the Master unless it has higher priority. This eliminates service disruption unless a more preferred path becomes
available.

Reference: https://tools.ietf.org/html/rfc3768

Question 13

Comments
  1. CCNP life
    August 15th, 2017

    Can someone please explain Question 3 ?

  2. cl
    August 30th, 2017

    question 3 makes no sense. The answer seems odd also

  3. BoZZ
    August 30th, 2017

    Q3 – VRRP can have multiple groups per vlan (1-255). VLAN number and VRRP Group number DOES NOT need to match.

  4. ntwkninja
    August 31st, 2017

    @BoZZ Can you explain a little more? The correct answer is the selection where the VLAN number and VRRP group number match.

  5. Lucky
    September 3rd, 2017

    Q3 – VRRP default priority is 100. Hence, between answers A and B, A is correct because there is no need to manually configure priority to 100 as shown in answer B.

  6. Hank
    October 9th, 2017

    For Q5: where is the entire diagram for premium, members?
    The answer says PC 1 and 3…but I do not see whole diagram.

  7. Mark
    October 10th, 2017

    @Hank
    Diagram missing, just trust it :)

  8. Rizwan
    October 11th, 2017

    where is the diagram for Q7?

  9. xjuankx
    October 12th, 2017

    Premiuns no found diagram… =(

  10. xjuankx
    October 12th, 2017

    Q3 –> vrrp Priority default 100 ( Vlan is not a bug the vlan may be different )

  11. Al
    November 3rd, 2017

    Hi,

    Regarding Q 9. why D not A?

    Authentication commands must be entered under the interface. can you enter it somewhere else?

    Would inserting the same ip address on both interfaces involved in the vrrp election and Virtual ip interface work?!

    Thanks.

  12. mills
    November 7th, 2017

    Hello AI,

    With VRRP, the VIP and an interface on the L3 switch or router can share/have the same ip address. The authentication command is entered under the interface in VRRP, same for HSRP and GLBP.

    I feel D and E are both correct because they are features unique to VRRP.

  13. CCNP
    March 5th, 2018

    question 10 and 11 are missing in questions.

  14. pattap
    March 28th, 2018

    Q3 is so vague!!

    The below is from cisco website:

    Configuring VRRP Priority
    The valid priority range for a virtual router is from 1 to 254 (1 is the lowest priority and 254 is the highest).
    The default priority value for backups is 100. For devices whose interface IP address is the same as the primary virtual IP address (the master), the default value is 255.

    C. So according to the above,IP address of the int van 1 is the same as the primary virtual IP of vrrp group 1 making it the master of the party

    B. addresses are different making it backup, default is 100 – cisco doesn’t like us to repeat default config?

    A. again this is back up, default is 100 but we are trying to achieve some shenanigans here
    and decided to have it as 200

    I would probably go for A but each of the examples is valid, cisco really needs to stop this kind of questions, this is not even about knowing stuff but trying to figure what the hell they want

  15. pattap
    March 28th, 2018

    Q4

    A. VRRP uses multicast address 224.0.0.18
    C. VRRP uses protocol identifier 112

    no need to explain this one

  16. lalaversa
    May 6th, 2018

    Q3.
    People, like Lucky comment, priority 100 is default parameter and it will be not visible in configuration, then correct answer is A (the Q is “which statement is TRUE”)

  17. lalaversa
    May 6th, 2018

    Q5.
    It’s impossible answer correctly without a draw of PCs connections correlate to the exhibit. The only correct answer reading the question is surely “D”…. the other answer live in fantasy world…

  18. lalaversa
    May 6th, 2018

    Q7.
    Answer wrong !!! Correct are B D E.
    The configuration VRRP priority of the interface is 105, correct D (track eventually decrement 15, then it’s not to be 120 like on answer A… ask actually priority doesn’t that will be).
    In exibit track object1 is in state down then tracking is starting and decrement priority to 95 asap… also B is correct togheter answer E (if another router has priority default at least).
    Pitfall Q&A because B is correct only if E is correct.

  19. lalaversa
    May 6th, 2018

    Q9.
    D and E are correct answers but also A is not wrong.
    This Q&A will have two or three answers ? If it will be two, E is sure…. but for A or D the choise is very hard…
    Usually black hole to make the answer wrong.

  20. lalaversa
    May 6th, 2018

    Q10.
    too vague, let’s trust the answer….

  21. lalaversa
    May 6th, 2018

    Q11.
    like Q10, too vague, let’s trust the answer….

  22. Anonymous
    May 28th, 2018

    Today I passed my exam, I was asked the questions q3 q6 q12 q13

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    May 30th, 2018

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  24. terrance
    May 31st, 2018

    can someone explain Q5? I don’t understand it

  25. terrance
    May 31st, 2018

    Q7 also makes no sense?? how is the priority 120? it says 105, and if it is decremented by 15 it would be 90??

  26. Raito
    June 11th, 2018

    Q7:

    Priority is 95 AFTER it has been decremented by 15, because you can see that the interface which is tracked is already in state DOWN. So 95 + 15 = 120, which must have been manually configured.

    But I do not get why the master router cannot be preempted if some other router has a higher priority?

  27. nataliya
    June 22nd, 2018

    Q5
    impossible to answer wihtout PC’s configuration, but it is missing

  28. bloke
    June 24th, 2018

    Q7:
    A, C, E is also correct. Priority 105 is after decrement from 120 tested on real equipment

  29. Anonymous
    July 21st, 2018

    @Raito, 95 + 15 = 120? Oh dear…

  30. BoxingSurfer
    August 17th, 2018

    Q9:
    C, D, and E are all valid VRRP configurations
    But C is the ‘most’ correct.
    The reason is that ‘preempt’ is enabled by default on VRRP (its off by default in HSRP)
    So with answers D and E, the presence of this command makes them less correct than C

  31. Terranova
    September 17th, 2018

    Hi 9tut, regarding question 9 in the VRRP quizes it says the right answer is “the priority of the interface is 120” but in the output it says 105. Can you check on that and let me know please. Thank ou

  32. Dany1
    September 24th, 2018

    Regarding Q9 the 9tut answers are correct. The priority of interface is 120.
    For those who post other answers, please check on real switches or GNS3.
    When track is up (on GNS3) in “show vrrrp” output is priority 120 and when track is down, GNS3 show vrrp output is 105(cfgd 120). In question 9 that part (cfg 120) is missing to verify your knowledge

  33. Thirsty Fish
    September 27th, 2018

    Hey Dany1, thanks for replying, is that a default setting when it shows 105 on GNS3? and what do you mean cfg 120 is missing?

  34. cybernet
    October 23rd, 2018

    in Q7 why answer is A (A. The configured VRRP priority of the interface is 120)

  35. Sinan Al-Shoker
    November 18th, 2018

    Answer A is correct because skew time-> (256-configured priority)/256-configured.Answer C is correct because there was priority 105 in exhibit but there was also line: Track object 1 state “down” decrement 15 -> so the configured priority is 120.Answer E is NOT correct because even though the hello interval in the exhibit is 1s (hold interval is 3x hello + skew time (0.351)) but notice that there was hold down timer 3.351 instead of 3.531.

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