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HSRP Questions 4

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

Question 1

Question 2

Explanation

This HSRP MAC address is a virtual MAC address, 0000.0C07.ACxy, where xy is the HSRP group number in hexadecimal based on the respective interface. 25 in hexadecimal is 37 in decimal.

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Comments
  1. trueteller
    December 28th, 2018

    Q7
    I have checked this in GNS3.
    A is correct. However I can’t agree with E.
    There is a mistake in configuration of IP address. When VIP is not in the same subnet as interface address the state of HSRP is INIT on SW2.

    SW2#show standby
    Vlan1 – Group 20
    State is Init (virtual IP has invalid subnet)
    Virtual IP address is 192.168.250.1 (wrong subnet for this interface)
    Active virtual MAC address is 0000.0c07.ac14 (MAC Not In Use)
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Preemption disabled
    Active router is 192.168.250.2, priority 120 (expires in 10.656 sec)
    Standby router is unknown
    Priority 110 (configured 110)
    Group name is “hsrp-Vl1-20” (default)

    It acknowledges SW1 as an active because it receives the traffic destined for multicast group 224.0.0.2. However SW1 doesn’t recognize it standby state at SW2 doesn’t proceed with it beyond INIT state. I have checked version 2 of HSRP. Still the same result.
    I guess there is a misconfiguration of SW2 interface address. No other answer is valid with current config. If the configuration of SW2 interface was correct (192.168.250.3), the answer E would be correct.

  2. faze
    March 15th, 2019

    Hi, can someone please explain Q4? wouldn’t the answer be a misconfig?

  3. Network_Monkey
    March 19th, 2019

    Hi @faze,

    Yes you are right.
    In other certprepare Qs, it is misconfig.
    I think it needs to be double checked.

    Thanks

  4. Q4
    March 24th, 2019

    @faze
    read somewhere that you need to look at the actual error log
    if same virtual mac = l2 loop
    if diff virtual mac = hsrp misconfig

  5. UncleJ
    April 19th, 2019

    What about Q1?
    All groups? All HSRP groups in the router? Each HSRP group has their own same VIP and virtual MAC, isn’t it?

    Can anyone clear up this question?

  6. Abdullah
    September 10th, 2019

    Q9
    In HSRP and VRRP, only the primary router is used to forward traffic, others routers must wait for the primary one down before they are used. Also, the bandwidth of the standby (and other) routers are not used and wasted. With GLBP, up to four gateways can be used simultaneously. There is still one virtual IP address in a group, but GLBP can automatically select which router in the group to forward traffic by sending the virtual MAC address of a selected router to that host.

    Question 2

    Which two statements are true about HSRP, VRRP, and GLBP? (Choose two)

    A. GLBP and VRRP allow for MD5 authentication, whereas HSRP does not.
    B. HSRP allows for multiple upstream active links being simultaneously used, whereas GLBP does not.
    C. GLBP allows for router load balancing of traffic from a network segment without the different host IP configurations required to achieve the same results with HSRP.
    D. Unlike HSRP and VRRP, GLBP allows automatic selection and simultaneous use of multiple available gateways.
    E. GLBP allows for router load balancing of traffic from a network segment by utilizing the creation of multiple standby groups.

  7. Abdullah
    September 10th, 2019

    Answer: C D

  8. Dmytro
    September 15th, 2019

    About Q4, a very similar question was in section “HSRP Questions” (without number) Q7, and answer was misconfigure.

  9. Rothgar
    September 26th, 2019

    Don’t Q8 and Q9 conflict? Does Q8 mean to say “GLBP can share multiple MAC for gateway load balancing?”

  10. Dmytro
    October 17th, 2019

    I think that Q8 and Q9 are the same, so Q9 right answer might be the variant:
    C. Only HSRP can use multiple MAC address to provide gateway load balancing over multiple routers

  11. Burìk
    November 1st, 2019

    Q7

    Well, I just gave it a try with real hardware *and* the correct IP address on R1, assuming there is a typo in the exhibit.

    R1#show running-config interface fastEthernet 0
    Building configuration…

    Current configuration : 149 bytes
    !
    interface FastEthernet0
    ip address 192.168.250.2 255.255.255.0
    speed 100
    full-duplex
    standby 20 ip 192.168.250.1
    standby 20 priority 120
    end

    R2#show running-config interface fastEthernet 0
    Building configuration…

    Current configuration : 149 bytes
    !
    interface FastEthernet0
    ip address 192.168.250.3 255.255.255.0
    speed 100
    full-duplex
    standby 20 ip 192.168.250.1
    standby 20 priority 110
    end

    R1#show standby
    FastEthernet0 – Group 20
    State is Active
    2 state changes, last state change 00:10:30
    Virtual IP address is 192.168.250.1
    Active virtual MAC address is 0000.0c07.ac14
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Next hello sent in 2.584 secs
    Preemption disabled
    Active router is local
    Standby router is 192.168.250.3, priority 110 (expires in 9.852 sec)
    Priority 120 (configured 120)
    IP redundancy name is “hsrp-Fa0-20” (default)

    R2#show standby
    FastEthernet0 – Group 20
    State is Standby
    9 state changes, last state change 00:04:44
    Virtual IP address is 192.168.250.1
    Active virtual MAC address is 0000.0c07.ac14
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.080 secs
    Preemption disabled
    Active router is 192.168.250.2, priority 120 (expires in 9.804 sec)
    Standby router is local
    Priority 110 (configured 110)
    IP redundancy name is “hsrp-Fa0-20” (default)

    R2#debug standby events
    HSRP Events debugging is on

    *** R1 GOES DOWN *** [power off]

    R2#
    *Jan 1 00:43:13.139: HSRP: Fa0 Grp 20 Standby: c/Active timer expired (192.168.250.2)
    *Jan 1 00:43:13.139: HSRP: Fa0 Grp 20 Active router is local, was 192.168.250.2
    *Jan 1 00:43:13.139: HSRP: Fa0 Grp 20 Standby router is unknown, was local
    *Jan 1 00:43:13.139: HSRP: Fa0 Grp 20 Standby -> Active
    *Jan 1 00:43:13.139: %HSRP-6-STATECHANGE: FastEthernet0 Grp 20 state Standby -> Active
    *Jan 1 00:43:13.139: HSRP: Fa0 Grp 20 Redundancy “hsrp-Fa0-20” state Standby -> Active
    *Jan 1 00:43:13.139: HSRP: Fa0 Redundancy server “hsrp-Fa0-20” update, Standby -> Active
    *Jan 1 00:43:16.139: HSRP: Fa0 Grp 20 Redundancy group hsrp-Fa0-20 state Active -> Active
    *Jan 1 00:43:19.139: HSRP: Fa0 Grp 20 Redundancy group hsrp-Fa0-20 state Active -> Active
    R2#show standby
    FastEthernet0 – Group 20
    State is Active
    10 state changes, last state change 00:00:26
    Virtual IP address is 192.168.250.1
    Active virtual MAC address is 0000.0c07.ac14
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Next hello sent in 0.648 secs
    Preemption disabled
    Active router is local
    Standby router is unknown
    Priority 110 (configured 110)
    IP redundancy name is “hsrp-Fa0-20” (default)

    *** R1 COMES BACK UP *** [power on]

    *Jan 1 00:46:43.007: HSRP: Fa0 Grp 20 Hello in 192.168.250.2 Active pri 120 vIP 192.168.250.1
    *Jan 1 00:46:43.007: HSRP: Fa0 Grp 20 Active router is 192.168.250.2, was local
    *Jan 1 00:46:43.007: HSRP: Fa0 Grp 20 Active: g/Hello rcvd from higher pri Active router (120/192.168.250.2)
    *Jan 1 00:46:43.007: HSRP: Fa0 Grp 20 Active -> Speak
    *Jan 1 00:46:43.007: %HSRP-6-STATECHANGE: FastEthernet0 Grp 20 state Active -> Speak
    *Jan 1 00:46:43.007: HSRP: Fa0 Grp 20 Redundancy “hsrp-Fa0-20” state Active -> Speak
    *Jan 1 00:46:43.007: HSRP: Fa0 Redundancy server “hsrp-Fa0-20” update, Active -> Speak
    *Jan 1 00:46:53.007: HSRP: Fa0 Grp 20 Speak: d/Standby timer expired (unknown)
    *Jan 1 00:46:53.007: HSRP: Fa0 Grp 20 Standby router is local
    *Jan 1 00:46:53.007: HSRP: Fa0 Grp 20 Speak -> Standby
    *Jan 1 00:46:53.007: %HSRP-6-STATECHANGE: FastEthernet0 Grp 20 state Speak -> Standby
    *Jan 1 00:46:53.007: HSRP: Fa0 Grp 20 Redundancy “hsrp-Fa0-20” state Speak -> Standby
    *Jan 1 00:46:53.007: HSRP: Fa0 Redundancy server “hsrp-Fa0-20” update, Speak -> Standby

    R2#show standby
    FastEthernet0 – Group 20
    State is Standby
    12 state changes, last state change 00:00:55
    Virtual IP address is 192.168.250.1
    Active virtual MAC address is 0000.0c07.ac14
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Next hello sent in 1.172 secs
    Preemption disabled
    Active router is 192.168.250.2, priority 120 (expires in 7.640 sec)
    Standby router is local
    Priority 110 (configured 110)
    IP redundancy name is “hsrp-Fa0-20” (default)

    R1#show standby
    FastEthernet0 – Group 20
    State is Active
    2 state changes, last state change 00:01:45
    Virtual IP address is 192.168.250.1
    Active virtual MAC address is 0000.0c07.ac14
    Local virtual MAC address is 0000.0c07.ac14 (v1 default)
    Hello time 3 sec, hold time 10 sec
    Next hello sent in 2.888 secs
    Preemption disabled
    Active router is local
    Standby router is 192.168.250.3, priority 110 (expires in 7.420 sec)
    Priority 120 (configured 120)
    IP redundancy name is “hsrp-Fa0-20” (default)

    So even though Preemption is disabled, R1 goes back to Active state when it comes back online and R2 goes back to Standby.

    Why so? Theory says that without Preemption, roles should stay the same, right? NO.
    Preemption is used only in conjunction with interface tracking, you do NOT need preemption if you just want the Standby router to become Active when the current Active goes *physically down* [i.e. the current Standby router loses contact with the current Active]
    Note the “If R1 goes DOWN” in the question.

    So, assuming there’s a typo in the question regarding the IP address, correct answers are A and D.

    https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/13780-6.html

  12. Burìk
    November 17th, 2019

    Q7 – again

    After digging through more questions related to preemption I noticed that the Correct Cisco Answer™ here is indeed E. Cisco theory does not take into account real-world scenarios where routers that fail to communicate with each other will both keep their Active roles until a communication is re-established, at that point R2 will renounce its Active state and revert back to Standby. But to properly answer this question the Cisco way we have to pick A and E, because if Hello packets are exchanged *before* R1 is finished booting and therefore it doesn’t have enough time to elect itself as Active, it will indeed need to preempt R2 to take back its Active role.

  13. Q7
    November 18th, 2019

    Q7 – it must be related to IOS version. I’ve checked this and router with higher priority stayed Standby after reloading. In my case it was 12.4(17a) IOS version.

  14. Burìk
    December 1st, 2019

    Actually it depends on what goes up first, either the HSRP system or the links between the two routers. Even without Preemption, if R1 elects itself as Active because it can’t talk to R2 yet, once the links between the two routers go up and Hello packets are exchanged, R2 will resign its Active role. However, if Hello packets are exchanged before R1 elects itself as Active, R2 won’t resign its Active role. In my home lab I have a bunch of routers ranging from IOS 12 to 15 and they all act the same.

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