Gateway Redundancy Questions
Here you will find answers to HSRP, VRRP and GLBP questions
Quick summary:
HSRP, VRRP, or GLBP is used to allow specific routers to appear as a single router to make the failover transparent to the end users.
Question 1:
You have just purchased a new Cisco 3550 switch running the enhanced IOS and need to configure it to be installed in a high availability network. Which three types of interfaces can be used to configure HSRP on a 3550 EMI switch? (Choose three)
A – BVI interface
B – routed port
C – SVI interface
D – Access port
E – EtherChannel port channel
F – Loopback Interface
Answer: B C E
Explanation:
To configure HSRP, a Layer 3 interface is needed. They can be:
- Routed port: a physical port configured as a Layer 3 port by entering the no switchport interface configuration command.
– SVI: a VLAN interface created by using the interface vlan vlan_id global configuration command and by default a Layer 3 interface.
– Etherchannel port channel in Layer 3 mode: a port-channel logical interface created by using the interface port-channel port-channel-number global configuration command and binding the Ethernet interface into the channel group.
Reference:
Question 2:
You work as a network technician , study the exhibit carefully. Which two statements are true about the output from the show standby vlan 50 command? (Choose two)
| Catalyst_A# show standby vlan 50 VLAN50 – Group 1 Local State is Active, priority 200 may preempt Hellotime 3 sec, holdtime 10 sec Next hello sent in 1.302 Virtual IP address is 192.168.1.1 configured Active router is local Standby router is 192.186.1.11 expires in 9.443 Virtual MAC address is 0000.0c07.ac01 Authentication text ”AuthenKey” 2 state changes, last state change 00:11:30 IP redundancy name is “hsrp-Vl150-1″ (default)
VLAN50 -Group 2 |
A. Catalyst_A is load sharing traffic in VLAN 50.
B. Hosts using the default gateway address of 192.168.1.2 will have their traffic sent to Catalyst_A.
C. The command standby 1 preempt was added to Catalyst_A.
D. Hosts using the default gateway address of 192.168.1.1 will have their traffic sent to 192.168.1.11 even after Catalyst _A becomes available again.
Answer: A C
Explanation:
The output shows that the Catalyst_A switch is the active router for HSRP group 1 and the standby router for HSRP group 2 on interface VLAN 50. This means that another switch is the active router for HSRP group 2 on interface VLAN 50 -> A is correct, Catalyst_A is load sharing traffic in VLAN 50.
B is not correct, only hosts using the default gateway address of 192.168.1.1 will have their traffic sent to Catalyst_A
From the output, we notice that there is a line showing that “Local State is Active, priority 200 may preempt”. This indicates the command “standby 1 preempt” was added to Catalyst_A. If the active router (this router) fails, another router takes over its active role. The original active router is not allowed to resume the active role when it is restored until the new active router fails. Pre-empting allows a higher-priority router to take over the active role immediately.
Question 3:
You are a network technician, study the exhibit carefully. Both routers are configured for the Gateway Load Balancing Protocol (GLBP). Which statement is true?
A. The default gateway address of each host should be set to the virtual IP address.
B. The default gateway addresses of both hosts should be set to the IP addresses of both routers.
C. The hosts will have different default gateway IP addresses and different MAC addresses for each.
D. The hosts will learn the proper default gateway IP address from Router RA.
Answer: A
Question 4:
You are a network technician, study the exhibit carefully. Assume that Host PC can ping the Corporate Headquarters and that HSRP is configured on DS1, which is then reloaded. Assume that DS2 is then configured and reloaded. On the basis of this information, what conclusion can be drawn?
| DS1# show running-config
interface Vlan10 |
DS2# show running-config
interface Vlan10 |
A. DS1 will be the active router because it booted first.
B. DS1 will be the standby router because it has the lower IP address.
C. DS1 will be the active router because it has the lower priority configured.
D. DS2 will be the active router because it booted last.
Answer: A
Explanation:
The configuration does not have the “standby 60 preempt”command so the first booted router will take the active role with any priority.
Question 5:
HSRP is a Cisco-proprietary protocol developed to allow several routers (or multilayer switches) to appear as a single gateway address. Which two statements are true about the Hot Standby Router Protocol (HSRP)? (Choose two)
A – Load sharing with HSRP is achieved by creating multiple subinterfaces on the HSRP routers.
B – Routers configured for HSRP can belong to multiple groups and multiple VLANs.
C – All routers configured for HSRP load balancing must be configured with the same priority.
D – Load sharing with HSRP is achieved by creating HSRP groups on the HSRP routers.
Answer: B D
Question 6:
If you are a network technician, study the exhibit carefully. Which Virtual Router Redundancy Protocol (VRRP) statement is true about the roles of the master virtual router and the backup virtual router?
| RA(config)# interface f0/0 RA(config-if)# ip address 10.0.0.1 255.255.255.0 RA(config-if)# vrrp 1 priority 110 RA(config-if)# vrrp 1 ip 10.0.0.10 |
| ——————————————————————— RB(config)# interface f0/0 RB(config-if)# ip address 10.0.0.2 255.255.255.0 RB(config-if)# vrrp 1 priority 100 RB(config-if)# vrrp 1 ip 10.0.0.10 |
A – Router RA is the master virtual router, and Router RB is the backup virtual router. When Router RA fails, Router RB will become the master virtual router. When Router RA recovers, Router RB will maintain the role of master virtual router.
B – Router RA is the master virtual router, and Router RB is the backup virtual router. When Router RA fails, Router RB will become the master virtual router. When Router RA recovers, it will regain the master virtual router role.
C – Router RB is the master virtual router, and Router RA is the backup virtual router. When Router RB fails, Router RA will become the master virtual router. When Router RB recovers, RouterRA will maintain the role of master.
D – Router RB is the master virtual router, and Router RA is the backup virtual router. When Router RB fails, Router
RA will become the master virtual router. When Router RB recovers, it will regain the master virtual router role.
Answer: B
Explanation:
Router RA is the master virtual router because of its higher priority (110). By default, the pre-empting function is enabled so Router RB will become the master virtual router when RA fails; and when RA recovers, it will take the master role again.
Question 7:
You are a network technician, do you know which three statements are correct about a default HSRP configuration? (Choose three)
A – The Standby track interface priority is 10.
B – The Standby priority is 100.
C – The Standby hold time is 10 seconds.
D – Two HSRP groups are configured.
Answer: A B C
Question 8:
You work as a network technician at Technical Corporation. Your boss is interested in GLBP. Study the network topology exhibit carefully. Which three statements accurately describe this GLBP topology? (Choose three)
A – If RA becomes unavailable, RB will forward packets sent to the virtual MAC address of RA.
B – RA is responsible for answering ARP requests sent to the virtual IP address.
C – If another router were added to this GLBP group, there would be two backup AVGs.
D – RA alternately responds to ARP requests with different virtual MAC addresses.
Answer: A B D
Explanation:
If RA fails, the GLBP protocol informs RB to replace the AVG that is down. The new AVG (in this case RB) will forward the packet sent to the 0008.b400.0101 virtual mac address, so the client sees no disruption of service nor does it need to resolve a new MAC address for the default gateway. -> A is correct.
RA, which is the AVG, replies to the ARP requests from clients with different virtual MAC addresses, thus achieving load balancing -> B is correct.
RA is elected as the AVG and RB is elected as the standby virtual gateway. If another router is added to this GLBP group, it will become a backup AVG -> there is only one backup AVG -> C is not correct.
“RA alternately responds to ARP requests with different virtual MAC addresses” this is the way GLBP provides load balancing over multiple routers (gateways) using a single virtual IP address and multiple virtual MAC addresses. Which MAC address it returns depends on which load-balancing algorithm it is configured to use -> D is correct.
Question 9
Which three protocols have been developed for IP routing redundancy to protect against first-hop router failure? (Choose three)
A. GLBP
B. ICMP
C. MSTP
D. HSRP
E. VRRP
F. NHRP
Answer: A D E
Explanation
All three protocols above are used for IP routing redundancy to protect against first-hop router failure. Some main differences of them are listed below:
HSRP: is a Cisco proprietary protocol.
VRRP: Open standard, created by IETF
GLBP: is a Cisco proprietary protocol. It is the only protocol (in three) supports load-balancing.
hi.thank you admin.that’s very good.
Top Banana – thanks very much for the explanations
J
Difficult topic.
thank you certprepare
sweet
In GLBP, When the failed AVG comes back up, does it take over the roll from the backup AVG again? as is done in the VRRP protocol where “pre-empting” function is enabled by default.
That’s a good question..
Unlike VRRP that has the preempt ability enabled, GLBP as in HSRP needs to be configured for a recovered unit to take over as the AVG.
Switch(config-if)#glbp 1 preempt
HI
As to Q6:
Imho the statement “By default, the pre-empting function is enabled” is wrong.
Afaik pre-emption has to be set manually!?
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Ah! Oh! This is VRRP!!!!
I just found in RFC 3768:
“Preempt_Mode Controls whether a higher priority Backup
router preempts a lower priority Master.
Values are True to allow preemption and False
to prohibit preemption. Default is True.”
So You’re Right! Sorry for confusing!
Hi, based on question 8, i have a doubt on option C. Official cisco documentation says (http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1049074)
“(…)Other group members provide backup for the AVG in the event that the AVG becomes unavailable(…)”. In brief i understood that a GLBP group is composed as following:
-one AVG
-othjer members are AVF and at the same time backup AVG
What do you think?
Ciao, Fabio.
@fabio
Based on your link, GLBP operates virtual gateway redundancy in the same way as HSRP. One gateway is elected as the AVG, another gateway is elected as the standby virtual gateway, and the remaining gateways are placed in a listen state.
If an AVG fails, the standby virtual gateway will assume responsibility for the virtual IP address. A new standby virtual gateway is then elected from the gateways in the listen state.
Virtual forwarder redundancy is similar to virtual gateway redundancy with an AVF. If the AVF fails, one of the secondary virtual forwarders in the listen state assumes responsibility for the virtual MAC address.
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By default, all VRRP routers are configured to preempt the current master router if their
priorities are greater.
Q.No2 You work as a network technician , study the exhibit carefully. Which two statements are true about the output from the show standby vlan 50 command? (Choose two)?
According to p4s A & B
But According to certprepare A & C
Which One is right ?
@qamar CertPrepare is right. It can’t be B because Catalyst_A is the standby switch for group 2, not the active. You can verify this with the line “Standby router is local” in the show command. Read the description for the rest.
Thus the correct answers are A & C.
dint know vrrp has the preempt feature enabled.. am so liking this site!!
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for question 3, i think the answer shud be D. (The hosts will learn the proper default gateway IP address from Router RA.). The protocol here is GLBP, and the advantage of running GLBP is it saves the labour of configuring gateway ip addressess on each of the client machine unlike HSRP, where manual configuration is required. As given on page 281 in switch book it says “The advantage is that none of the client has to be pointed towards specific gateway addresses…”.
I guess what the book was saying that in order to load balance, we don’t need to point towards different gateways. Without GLBP, you have to config some hosts to RA and some to hosts to RB.
The only method to learn a default gateway automatically is via DHCP only and since there is no DHCP server here, therefore D is not correct. Even then, you still need the DHCP server to provide the virtual IP to the hosts.
Hope this clarifies
Correct cisco. RA is not supplying IP information to the host. That is a DHCP function. Once the host has recieved its dhcp information from wherever the server is located, RA is simply supplying the MAC address for the gateway that was given to the host via the DHCP server.
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Question 6, it doesn’t show that it has been preemp in the command… Hence I beleive ans A shoule be correct.. Please correct me if I am wrong here…
Thanks…
@Yankee!
For VRRP,By default, the pre-empting function is enabled.
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Hello, I am confused about a thing:
-In the ciscopress book it says that VRRP has not interface tracking. I have worked with VRRP in Juniper and it has.
-In the ERRATA of the book, they fixed it and says that VRRP has interface tracking and add the configuration of interface tracking.
-In the P4s 478Q is a question that asks which protocol has not interface tracking, and the answer is VRRP!!
I am sure VRRP has tracking. Please someone!
@VRRP Tracking, in this link you can see that Interface Tracking is not a VRRP feature, however you can use the object track feature that extends the capabilities of VRRP and you can use for decrement group priority, so that is the reason why P4S says that VRRP has not interface tracking!..
http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtvrrptk.html
Q7 , a) –> “The Standby track interface priority is 10.” –> should be –> ” The Standby track interface DECREMENT is 10.”
still D can’t be right ;)
why b is correct ? (etherchannel)
AMIRA, I noticed that too. – It should be “decrement” instead of priority.
For question 7. I saw this question on a dump with the same graphic, what would be the correct answers for this? Choose 4
A. Router A is responsible for answering ARP requests sent to the virtual IP address.
B. If Router A becomes unavailable, Router B will forward packets sent to the virtual MAC address of Router A.
C. Router A alternately responds to ARP requests with different virtual MAC addresses.
D. Router B will transition from blocking state to forwarding state when it becomes the AVG.
E. If another router were added to this GLBP group, there would be two backup AVGs.
F. Router B is in GLBP listen state.
So I Know its ABE whats the 4th
Thanks
2Lobo, I don’t think its ABE, I think ABCF.
@Dmitry Thank You for the help, I looked it up and your answers are correct.
Q4 on this link http://www.certprepare.com/glbp-questions is similar to Q8 on this page. Why “If another router were added to this GLBP group, there would be two backup AVGs.” choice is correct on the link I provided, and it is wrong on this page? Correct me if I am missing anything. Thank you!
Hi Nani,
I think the answer on the other page “If another router were added to this GLBP group, there would be two backup AVGs.” is NOT correct.
In a GLBP group there can be only 1 AVG and 1 Standby Virtual Gateway and 4 AVF’s (which includes the AVG and the SVG) at the most. Any other gateways are placed in the GLBP listen state. There cannot be two backup AVG’s in a group.
This is from the Cisco website:
GLBP operates virtual gateway redundancy in the same way as HSRP. One gateway is elected as the AVG, another gateway is elected as the standby virtual gateway, and the remaining gateways are placed in a listen state. If an AVG fails, the standby virtual gateway will assume responsibility for the virtual IP address. A new standby virtual gateway is then elected from the gateways in the listen state.
Link: http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1039649
On second thoughts, I think the option…
“If another router were added to this GLBP group, there would be two backup AVGs.”
…might actually be correct.
The following is from the same Cisco link in my previous post for GLBP :
“Other group members provide backup for the AVG in the event that the AVG becomes unavailable.”
Its all about how the question is worded I guess! Maybe they mean it to be just like the port state versus role in STP.
The state of the new gateway is “listen” and the role is “backup”.
Question 8 in here and Question 4 in GLBP questions (link in the right) the answers seems to be contradictory for item “If another router were added to this GLBP group, there would be two backup AVGs.”
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Q8, all choices are correct.
For more information read CCNP Switch Foundation Learning Guide, page 217.
Q 8. There is only one backup AVG with the second highest priority or highest priority or highest IP Address among AVFs from which a backup AVG is chosen . All AVFs backup each other.
Q.8 So even if more of one router can act as AVG backup, only one will be choose, Am I right?
From Cisco Doc http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1039649
GLBP Gateway Priority
GLBP gateway priority determines the role that each GLBP gateway plays and what happens if the AVG fails.
Priority also determines if a GLBP router functions as a backup virtual gateway and the order of ascendancy to becoming an AVG if the current AVG fails. You can configure the priority of each backup virtual gateway with a value of 1 through 255 using the glbp priority command.
Q6 on test today
nothing from this section in test today.
Q8: there’s a similar question on http://www.certprepare.com/glbp-questions (Q4), and one of the valid answers was “If another router were added to this GLBP group, there would be two backup AVGs”, which is instead marked as incorrect on Q8 of this page. I guess this answer is also correct here on Q8, because we have to distinguish the two words: Standby and backup.
- Standby is the GLBP role/state itself and indeed at any time there cannot be more than one Standby per GLBP group;
- however, if there is a 3rd router in the group, we can consider it functioning as an additional backup to the AVG: in this sense we have to consider the word ‘backup’ as the effective function the third router does.
Regarding answer D (RA alternately responds to ARP requests with different virtual MAC addresses), we cannot tell for sure that the round-robin mechanism is in place, there could be weighting configured. I just tested it in GNS3, with 2 GLBP routers and 4 hosts attached:
RA with glbp 1 weighting 150
RB with glbp 1 weighting 100
- With this config the 4 hosts alternatively got RA’s and RB’s virtual MAC addresses, but this perfect alternation will eventually stop when other hosts do an ARP request for the default gateway. This is to say that if we see the 2 hosts in the question having 2 different virtual MAC address, it doesn’t necessarily mean that “RA alternately responds to ARP requests with different virtual MAC addresses” for ever.
Please correct me if I’m wrong on this.
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