Chapter 18 - HSRP

Question 1

How do you enable HSRP on a router?

Answer 1

Enter interface config mode:
(config-if)# standby 1 192.168.1.1
The “1” is the HSRP group that this interface belongs to and the 192.168.1.1 is the virtual IP that will be shared.

Question 2

How would you find the MAC address of a HSRP virtual IP?

Answer 2

show ip arp

Question 3

What are the first 10 characters of a HSRP version 1 virtual MAC address?

Answer 3

0000.0c07.ac
NOTE: the full MAC is 0000.0c07.ac01
The “01” at the end is the HSRP group number configured on the router’s interface standby command.

Question 4

What is the default HSRP priority value?

Answer 4

100

It can be any value between 0 and 255

Question 5

How do you manually assign a HSRP value to force election of an active router in a HSRP pair?

Answer 5

One way is to assign a higher priority than 100 on the router we want to be the active member of the pair.

(config-if)# standby 1 priority 110

Question 6

What does the “preempt” command do on an interface configured for HSRP?

Answer 6

Preempt allows a router that comes online with a higher HSRP priority to overthrow the current active router and become the new active router. The old one would go into a standby state.

Question 7

What happens if two routers come online at the exact same time with the same HSRP priority?

Answer 7

The router with the higher physical IP on the subnet wins.

Question 8

What are the differences of HSRPv1 and HSRPv2

Answer 8

• HSRP 2 supports IPv6
• Group numbers from 0-4095 (not just 0 - 255)
• Virtual MAC changes from 0000.0C07.ACXX to 0000.0C9FXXX
• Multicast changes from 224.0.0.2 to 224.0.0.102
• Different packet formats (HELLO messages, etc)

Question 9

How do you turn on HSRP version 2?

Answer 9

(config-if)# standby 1 version 2

Question 10

What is the minimum IOS code that will support HSRPv2?

Answer 10

12.2(46)SE and later

Question 11

What was the rationale of providing group numbers ranging from 0-4095 in HSRPv2?

Answer 11

More digits allows the HSRP group number / instance to match VLAN IDs.

Question 12

What are the 5 transition states of HSRP?

Answer 12

• Initial: The state at the start. Also, it is the state after a configuration change or when an interface first comes up.
• Listen: The router knows the virtual IP address. It listens for hello messages from other routers.
• Speak: The router sends periodic hello messages and actively participates in the election of the active or standby router.
• Standby: The router is a candidate to become the next active router and sends periodic hello messages.
• Active: The router currently forwards packets that are sent to the group virtual MAC address. The router sends periodic hello messages.