ICND2 – HSRP Questions

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Question 1

[am4show have=’p2;’]Which three statements about HSRP operation are true? (Choose three)

A. The virtual IP address and virtual MAC address are active on the HSRP Master router.
B. The HSRP default timers are a 3 second hello interval and a 10 second dead interval.
C. HSRP supports only clear-text authentication.
D. The HSRP virtual IP address must be on a different subnet than the routers’ interfaces on the same LAN.
E. The HSRP virtual IP address must be the same as one of the router’s interface addresses on the LAN.
F. HSRP supports up to 255 groups per interface, enabling an administrative form of load balancing.

 

Answer: A B F[/am4show]

Explanation

The virtual MAC address of HSRP version 1 is 0000.0C07.ACxx, where xx is the HSRP group number in hexadecimal based on the respective interface. For example, HSRP group 10 uses the HSRP virtual MAC address of 0000.0C07.AC0A. HSRP version 2 uses a virtual MAC address of 0000.0C9F.FXXX (XXX: HSRP group in hexadecimal)

For more information about HSRP operation, please read our HSRP tutorial.

Question 2

[am4show have=’p2;’]What is a valid HSRP virtual MAC address?

A. 0000.5E00.01A3
B. 0007.B400.AE01
C. 0000.0C07.AC15
D. 0007.5E00.B301

 

Answer: C[/am4show]

Explanation

With HSRP, two or more devices support a virtual router with a fictitious MAC address and unique IP address. There are two version of HSRP.

+ With HSRP version 1, the virtual router’s MAC address is 0000.0c07.ACxx , in which xx is the HSRP group.
+ With HSRP version 2, the virtual MAC address if 0000.0C9F.Fxxx, in which xxx is the HSRP group.

Note: Another case is HSRP for IPv6, in which the MAC address range from 0005.73A0.0000 through 0005.73A0.0FFF.

-> C is correct.

(Good resource for HSRP: http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_hsrp.html)

Question 3

[am4show have=’p2;’]Which three options are the HSRP states for a router? (Choose three)

A. initialize
B. learn
C. secondary
D. listen
E. speak
F. primary

 

Answer: B D E[/am4show]

Explanation

HSRP consists of 6 states:

State	Description
Initial	This is the beginning state. It indicates HSRP is not running. It happens when the configuration changes or the interface is first turned on
Learn	The router has not determined the virtual IP address and has not yet seen an authenticated hello message from the active router. In this state, the router still waits to hear from the active router.
Listen	The router knows both IP and MAC address of the virtual router but it is not the active or standby router. For example, if there are 3 routers in HSRP group, the router which is not in active or standby state will remain in listen state.
Speak	The router sends periodic HSRP hellos and participates in the election of the active or standby router.
Standby	In this state, the router monitors hellos from the active router and it will take the active state when the current active router fails (no packets heard from active router)
Active	The router forwards packets that are sent to the HSRP group. The router also sends periodic hello messages

Please notice that not all routers in a HSRP group go through all states above. In a HSRP group, only one router reaches active state and one router reaches standby state. Other routers will stop at listen state.

Question 4

[am4show have=’p2;’]What about HSRP IP Address is true?

A. If its part of the LAN
B. Part of all other networks
C. Local to the interface
D. Appears in the routing table
E. Acts as default route for that interface

 

Answer: E[/am4show]

Question 5

[am4show have=’p2;’]Which of the following HSRP router states does an active router enter when it is preempted by a higher priority router?

A. active
B. speak
C. learn
D. listen
E. init
F. standby

 

Answer: B[/am4show]

Explanation

First we should review all the HSRP States:

State	Description
Initial	This is the beginning state. It indicates HSRP is not running. It happens when the configuration changes or the interface is first turned on
Listen	The router knows both IP and MAC address of the virtual router but it is not the active or standby router. For example, if there are 3 routers in HSRP group, the router which is not in active or standby state will remain in listen state.
Speak	The router sends periodic HSRP hellos and participates in the election of the active or standby router.
Standby	In this state, the router monitors hellos from the active router and it will take the active state when the current active router fails (no packets heard from active router)
Active	The router forwards packets that are sent to the HSRP group. The router also sends periodic hello messages

Now let’s take an example of a router passing through these states. Suppose there are 2 routers A and B in the network; router A is turned on first. It enters the initial state. Then it moves to listen state in which it tries to hear if there are already active or standby routers for this group. After learning no one take the active or standby state, it determines to take part in the election by moving to speak state. Now it starts sending hello messages containing its priority. These messages are sent to the multicast address 224.0.0.2 (which can be heard by all members in that group). When it does not hear a hello message with a higher priority it assumes the role of active router and moves to active state. In this state, it continues sending out periodic hello messages.

Now router B is turned on. It also goes through initial and listen state. In listen state, it learns that router A has been already the active router and no other router is taking standby role so it enters speak state to compete for the standby router -> it promotes itself as standby router.

Now to our main question! We want router B to become active router so we set a higher priority number than the priority of A and ask router B to take over the role of active router (with the preempt command). Now router A will fall back to the speak state to compete for active or standby state -> it becomes standby router because its priority is now lower than that of router A. (Therefore answer B is correct).

Note: Suppose router A is in active state while router B is in standby state. If router B does not hear hello messages from router A within the holdtime, router B goes into speak state to announce its priority to all HSRP members and compete for the active state. But if at some time it receives a message from the active router that has a lower priority than its priority (because the administrator change the priority in either router), it can take over the active role by sending out a hello packet with parameters indicating it wants to take over the active router. This is called a coup hello message.

(Reference and good resource: http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtml)

Question 6

[am4show have=’p2;’]Which protocol specified by RFC 2281 provides network redundancy for IP networks, ensuring that user traffic immediately and transparently recovers from first-hop failures in network edge devices or access circuits?

A. ICMP
B. IRDP
C. HSRP
D. STP

 

Answer: C[/am4show]

Explanation

HSRP is a Cisco-proprietary protocol developed to allow several routers or multilayer switches to appear as a single gateway IP address. This protocol is described in RFC 2281.