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VRRP Questions

November 15th, 2019 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)
+ Default priority is 100

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
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  1. 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

  2. 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

  3. 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?

  4. cybernet
    October 23rd, 2018

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

  5. 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.

  6. Silas
    January 23rd, 2019

    question involving VRRP using protocol number 112 / RFC 5798 (a drag and drop)

  7. Daniel
    March 7th, 2019

    Thanks god just pass SW 300-115.
    TestKing dump is valid, labs are the same as cerprepare: LACP and HSRP. Not many new questions which similar to the dumps.
    Email me for dumps: ballking242 @ gmail dot com

  8. antran
    March 7th, 2019

    @NotMyRealName Thank you for the exhibit of Q11!

  9. Kasperl
    March 12th, 2019

    Q11
    10.10.1.1/32 must be in routing table because R1 is the VRRP Master

  10. Muhamad
    March 15th, 2019

    Pass on 13th march. My lab is HRSP and AAA dot1q. you should study them well.
    Few new questions, dump valid. Thanks Daniel for help!

    ====
    My email: muhamadawan1988(at)gmail(dot)com

  11. Anonymous
    April 13th, 2019

    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.

    Can anyone explaint to me please why is added and not subtracted if is a decrease?

  12. soho
    May 14th, 2019

    @Anonymous

    Note the line:
    Track object 1 state Down decrement 15

    The keyword DOWN means that the interface being tracked is DOWN currently.
    Remember this is a show output and the date provided is live data not running-config.
    Because the object is CURRENTLY “DOWN” the the decrement of 15 is now in place.
    So currently the decrement of 15 has been applied.
    This is why the output shows “Priority 105” because it is currently decremented by 15.

    If the line was:
    Track object 1 state Up decrement 15

    The interface is CURRENTLY showing as up.
    In turn the Priority line would say Priority 120.

  13. Q13
    May 29th, 2019

    I know it is nit-picky, but isn’t preemption enabled by default on vrrp?

    Also, any post that starts with “Thanks God” (They’re all over this website), don’t waste your time.

  14. Q7 answers are OK
    July 20th, 2019

    Q7 correct answers are OK. ACE.

    The same example on cisco site.
    https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/xe-3s/fhp-xe-3s-book/fhp-vrrp.html

    P.S. The funny thing is that virtual MAC address in Q7 has HSRP format not VRRP but it is just cosmetic issue in case of this question :)

  15. Dmytro
    October 10th, 2019

    About Q9, I think that variants D and E are really correct.
    Variant A is not so correct because they might be mean that you can use in VRRP authentication key chain, in that case you will config not all commands in interface configuration mode. Maybe that is why variant A is not completely right… but it is only my opinion.

  16. Habib Ullah
    December 3rd, 2019

    PC1 and PC3 using 10.1.0.1 and PC2 and PC4 using gateway 10.1.0.10

  17. Habib Ullah
    December 3rd, 2019

    Q5
    PC1 and PC3 using 10.1.0.1 and PC2 and PC4 using gateway 10.1.0.10

  18. Anon Passed
    January 3rd, 2020

    Just passed the exam! Used Zakaria’s material he posted few days ago as well as content from certprepare.
    Labs – HSRP, VTP and LACP with STP, all still valid.
    About 5-7 new questions but all very logical. The new questions are pretty much rephrased from the certprepare questions so as long you understand the concept, you will be fine :)
    Strangely only got 1 DND on TACACS and RADIUS

    The only question I remember from the exam that I didn’t see from certprepare is
    Which two accounting types does AAA support ?(choose two)
    Answer – System, Connection

    All the best guys! Just go through the material and you will pass.

  19. Anonymous
    January 16th, 2020

    where is ‘Zakaria’s material’ please.

  20. Kelvincenka
    January 19th, 2020

    @Anon could you please send the material here ? kelvincenka at gmail dot com

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