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GLBP Questions

November 15th, 2019 in SWITCH 300-115 Go to comments

Note: If you are not sure about GLBP, please read our GLBP tutorial.

Question 1

Explanation

The error message indicates a possible layer2 loop and STP configuration issues. Notice that the “duplicate address” here means the MAC address.

In order to resolve this issue, issue the show interface command to verify the MAC address of the interface. If the MAC address of the interface is the same as the one reported in the error message, then it indicates that this router is receiving its own hello packets sent. Verify the spanning-tree topology and check if there is any layer2 loop. If the interface MAC address is different from the one reported in the error message, then some other device with a MAC address reports this error message.

Reference: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/81565-glbp-cat65k.html#dr

Question 2

Explanation

The active virtual gateway (AVG) is responsible for answering the ARP Request for the virtual IP address. Load sharing is achieved by the AVG replying to the ARP requests with different virtual MAC addresses.

Question 3

Explanation

A GLBP group only has a maximum of four AVFs (means four virtual MAC addresses). If there are more than 4 gateways in a GLBP group then the rest will become Standby Virtual Forwarder (SVF) which will take the place of a AVF in case of failure.

Question 4

Question 5

Question 6

Explanation

GLBP members communicate between each other through hello messages sent every 3 seconds to the multicast address 224.0.0.102, User Datagram Protocol (UDP) port 3222 (source and destination).

Reference: http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html

Question 8

Question 9

Explanation

GLBP has three authentication schemes:

+ No authentication
+ Plain text authentication
+ MD5 authentication

Question 10

Question 11

Question 12

Question 13

Comments
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  1. Abdullah
    September 12th, 2019

    Q6
    Netbrain, totally agree. DE.

  2. Chaiwat Sarum
    September 25th, 2019

    Q13.
    Which two statements about GLBP is true? (Choose two)
    A. Can have 128 AVFs on an interface ==>Corect
    B. Maximum 4 AVFs allowed in a group ==>Correct
    C. Can work with dual active AVGs ==>not correct
    D. Can have 6 AVFs in a group ==>not correct
    E. GLBP supports up to 1024 virtual routers per group. ==>not correct

    I think answers : A,B Correct

    I read a book of David Hucaby page 380

    “Active Virtual Forwarder
    Each router participating in the GLBP group can become an AVF, if the AVG assigns it that role, along with a virtual MAC address. The virtual MAC addresses always have the form 0007.b4xx.xxyy. The 16-bit value denoted by xx.xx represents six 0 bits followed by a 10-bit GLBP group number. The 8-bit yy value is the virtual forwarder number”

  3. alba
    October 2nd, 2019

    Q6
    i think answer A is not correct.
    D & E is correct.

    https://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1039649

    A backup virtual gateway can become the AVG only if the current AVG fails, regardless of the priorities assigned to the virtual gateways. You can enable the GLBP preemptive scheme using the glbp preempt command. Preemption allows a backup virtual gateway to become the AVG, if the backup virtual gateway is assigned a higher priority than the current AVG.
    because A is not correct…

  4. BlueMoon
    October 9th, 2019
  5. Strummer
    October 24th, 2019

    It literally says in link you provided BlueMoon: “By default, the GLBP gateway preemptive scheme is disabled”

    ….

  6. suntzu
    February 19th, 2020

    I agree with @strummer,

    By default, the GLBP gateway preemptive scheme is disabled. A backup virtual gateway can become the AVG only if the current AVG fails, regardless of the priorities assigned to the virtual gateways. You can enable the GLBP preemptive scheme using the glbp preempt command. Preemption allows a backup virtual gateway to become the AVG, if the backup virtual gateway is assigned a higher priority than the current AVG

    @Alba
    You literally copy and paste the answer which shows A is one of the answers then say it is NOT an answer??????

    Which two statements about default FHRP behavior are true? (Choose two)

    A. A backup GLBP active virtual gateway can become active only if the current active virtual gateway fails
    B. Preemption is enabled by default
    C. Unless specifically configured, the priority of an HSRP router is 200
    D. A standby HSRP router becomes active if it has a higher priority than the priority of the current active router
    E. A VRRP backup virtual router becomes the master router if its priority is higher than the priority of the current master router

    A and E are the answers. I have NEVER seen a question on a test ask about “FHRP”. They always say the actual words like GLBP, HSRP or VRRP. This question is written wrong.

  7. suntzu
    February 19th, 2020

    @Chiawat

    GLBP supports up to 1024 virtual routers (GLBP groups) on each physical interface of a router, and up to 4 virtual forwarders per group.

    1024 virtual routers. What you posted has nothing to do with the number of virtual routers.

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