Volume 2 - Chapter 16: First Hop Redundancy Protocols

Question 1

What are the 3 main FHRPs?

Answer 1

Hot Standby Router Protocol (HSRP)
Virtual Router Redudancy Protocol (VRRP)
Gateway Load Balancing Protocol (GLBP)

Question 2

What type of FHRP is HSRP?

Answer 2

Active/Standy

Also know as Active/Passive

Question 3

Describe the procedure for electing the active router in a HSRP configuration.

Answer 3

1. The router with the highest configured pritority wins
2. If priorities tie, the router with the highest IP address wins
   3.

Question 4

True or False:

HSRP uses both a virtual IP and virtual MAC for the active default gateway IP.

Answer 4

True, the virtual router IP and MAC will be chosen by the network engineer

Question 5

Host A is connected to a subnet that has 3 routers configured with HSRP. Currently Router 1 is the active router.

What will Host A have in its ARP table for its default gateway?

Answer 5

The virtual IP and vMAC of the HSRP group, not Router 1’s interface.

Question 6

True or False:

In an HSRP configuration, when the current active router dies and the standby takes over, hosts will have to manually change their default gateway settings to the new active router.

Answer 6

False, all hosts in the subnet will point to the virtual IP as their default gateway which is configured across all routers in the HSRP group.

Question 7

Describe how HSRP can be configured for load balancing.

Answer 7

By default, only one router in the HSRP configuration is active. However, individual HSRP groups can be configured for each individual host subnet. For example:

• R1 is active for subnet 10.10.100.0 /24, while R2 is in standby
• R2 is active for subnet 10.20.100.0 /24, while R1 is in standby

Question 8

2 routers each with their own WAN connection are in a HSRP configuration. R1 is the current active router in the HSRP group.

R1 is online, but its connection to the WAN drops. How can a network engineer get traffic passing to R2 even though R1 is online and sending/receiving hellos.

Answer 8

HSRP will be configured on R1 to have a higher priority that R2 in normal circumstances. HSRP will also be configured so that if R1’s WAN interface goes down, R1’s priority drops and R2 takes over as the active router using preemption.

Question 9

Describe the function of preemption in regards to HSRP.

Answer 9

To have a router automatically become the active router if it has a higher priority than the current

Question 10

2 routers each with their own WAN connection are in a HSRP configuration. R1 is the current active router with a higher priority in the HSRP group. Preemption is not enabled.

R1 is online, but fails due to hardware issue and R2 becomes active. The network engineer repairs R1 and brings it online. What router will be the active router?

Answer 10

R2 will continue to be the active router even though R1 is online and has a higher priority.

Question 11

2 routers each with their own WAN connection are in a HSRP configuration. R1 is the current active router with a higher priority in the HSRP group. Preemption is enabled.

R1 is online, but fails due to hardware issue and R2 becomes active. The network engineer repairs R1 and brings it online. What router will be the active router?

Answer 11

R1 will take over as the active router because it has a higher priority and preemption is enabled.

Question 12

What does HSRP use to detect if the active router has failed?

Answer 12

Hello and send timers (similar to OSPF)

Question 13

True or False:

2 routers in an HSRP configuration can use different versions of HSRP.

Answer 13

False, in order for routers to successfully join an HSRP group, they must use the same version (version 1 or version 2)

Question 14

What version(s) of HSRP support IPv6?

Answer 14

Only HSRP version 2 supports IPv6, version 1 only supports IPv4

Question 15

Describe the differences between versions 1 & 2 of HSRP for hello timers.

Answer 15

Version 1 supports a timer in seconds whereas version 2 supports a timer in milliseconds

Question 16

What are the range of values for a version 1 HSRP group?

Answer 16

0 to 255

Question 17

What are the range of values for a version 2 HSRP group?

Answer 17

0 to 4095

Question 18

A network engineer configures a HSRP version 1 group with a group number of 8.

What will be the virtual MAC used by the virtual HSRP interface?

Answer 18

0000.0C07.ACxx, where xx is the group number in hex

0000.0C07.AC08

Question 19

A network engineer configures a HSRP version 1 group with a group number of 16.

What will be the virtual MAC used by the virtual HSRP interface?

Answer 19

0000.0C07.ACxx, where xx is the group number in hex

0000.0C07.AC10

Question 20

A network engineer configures a HSRP version 2 group with a group number of 20.

What will be the virtual MAC used by the virtual HSRP interface?

Answer 20

0000.0C9F.Fxxx, where xxx is the group number in hex

0000.0C9F.F014

Question 21

What is the multicast address used for HSRP version 1?

Answer 21

224.0.0.2

Question 22

What is the multicast address used for HSRP version 2?

Answer 22

224.0.0.102

Question 23

Describe how HSRP, VRRP, and GLBP differ in regards to preemption.

Answer 23

HSRP and GLBP have preemption disabled by default, whereas VRRP has it enabled by default.

Question 24

Describe how HSRP, VRRP, and GLBP differ in regards to the virtual IP for the group.

Answer 24

With VRRP, the virtual IP can be the same as one of the router’s physical interfaces.

With HSRP and GLBP, the virtual IP must be a unique IP address on the router.

Question 25

Describe how HSRP, VRRP, and GLBP differ in regards to load balancing.

Answer 25

All 3 protocols support load balancing.

However, only GLBP supports active/active load balancing in a single group. HSRP and VRRP only support load balancing by having different active routers for different groups

Question 26

What multicast address is used by VRRP?

Answer 26

224.0.0.18

Question 27

What is the valid range of values for a group number in VRRP?

Answer 27

1 to 255

Question 28

What is the valid range of values for a group number in GLBP?

Answer 28

0 to 1023

Question 29

What is the virtual MAC addres pattern used by VRRP?

Answer 29

0000.5e00.01xx

Question 30

What is the virtual MAC addres pattern used by GLBP?

Answer 30

0007.b40x.xxrr

Question 31

Describe how the MAC address of the virtual interface with GLBP differs from VRRP or HSRP.

Answer 31

With GLBP, each router in the group has a unique virtual MAC

With VRRP and HSRP, each route in the group share the same virtual MAC

Question 32

What would be the virtual MAC of a GLBP router that is designated as router 3 with a priority of 21?

Answer 32

0007.b400:1E02

01E represents the priority

02 represents the router number

Question 33

Describe how GLBP provides active load balancing within the single subnet.

Answer 33

The ARP table for each host is manipulated by the GLBP routers. Some hosts in the subnet will receive R1’s vMAC as the gateway, while others will recieve R2’s vMAC

Question 34

Describe the purpose of a GLBP active virtual gateway (AVG).

Answer 34

The router designated as the AVG handles the ARP requests from hosts on the subnet. For example;
* AVG tells PC1 that the gateway is R1’s vMAC
* AVG tells PC2 that the gateway is R2’s vMAC
* AVG tells PC3 that the gateway is R3’s vMAC

Question 35

Describe the purpose of a GLBP active virtual forwarder (AVF).

Answer 35

All routers in the GLBP topology serve as AVFs. Each AVF is ready to receive frames addressed to their unique vMAC.

Question 36

Describe what happens when the current AVG fails.

Answer 36

A new AVG is elected from the existing pool of AVFs.