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642-813 Q&A – Implement High Availability (31-35)

Section 5 – Implement High Availability, given a network design and a set of requirements

Which describes the default load balancing scheme used by the Gateway Load Balancing Protocol (GLBP)?
A.per host basis using a round-robin scheme
B.per host basis using a strict priority scheme
C.per session using a round-robin scheme
D.per session using a strict priority scheme
E.per GLBP group using a round-robin scheme
F.per GLBP group using a strict priority scheme
Answer: A

To provide a virtual router, multiple switches (routers) are assigned to a common GLBP group.
Rather than having just one active router performing forwarding for the virtual router address, all routers in the group can participate and offer load balancing by forwarding a portion of the overall traffic. The advantage is that none of the clients have to be pointed toward a specific gateway address-they can all have the same default gateway set to the virtual router IP address. The load balancing is provided completely through the use of virtual router MAC addresses in ARP replies returned to the clients. As a client sends an ARP request looking for the virtual router address,
GLBP sends back an ARP reply with the virtual MAC address of a selected router in the group.
The result is that all clients use the same gateway address but have differing MAC addresses for it.

What three tasks must a network administrator perform to properly configure Hot Standby Routing Protocol (HSRP)? (Select three)
A. Define the encapsulation type.
B. Define the standby router.
C. Define the standby IP address.
D. Enable the standby priority.
Answer: BCD
Three of the required configuration commands needed for enabling HSRP is to define the standby routing process, define the HSRP IP address, and configure the HSRP priority.
Configuring HSRP:
* Configuring an interface to participate in an HSRP standby group
* Assigning HSRP standby priority
* Configuring HSRP standby pre-empt
* Configuring HSRP over trunk links
* Configuring hello message timers
* HSRP interface tracking
* Displaying the status of HSRP
Incorrect Answers:
A: There are no encapsulation options for enabling HSRP.

Which protocol enables a group of routers to form a single virtual router and use the real IP address of a router as the gateway address?
A.Proxy ARP
Answer: D
The correct answer is VRRP whereby either a virtual or physical address can be chosen as the gateway address. If the physcial address of R2 is the gateway address, then R2 will become the gateway. If R2 goes down, R3 (or R4 etc) will become the gateway and will assume the IP address which, to it, will be a virtual one as none of its interfaces are configured with that address.
In this scenario. R2, R3 and R4 form one virtual router whereby R1’s physical addres is used as the gateway address. HSRP does not use physical addresses for the gateway at all.
Incorrect answer:
IRDP is not correct as it does not form a single virtual router. With IRDP, two possible gateways advertise themselves to the downstream router as potential gateways, one will be configured with a higher preference (lower IRDP preference number) than the other and so its physical interface will be elected as the gateway address. If this router becomes unavailable, the other router’s physical address will become the gateway address. No virtual routers or addresses are created.
For example, suppose R1 was configured for IRDP discovery and was connected to a segment with routers R2 and R3. If R2 was configured with irdp preference 20 and R3 was configured as irdp preference 30, R1 would select R2 as its gateway. If R2 was unavailable, R3 would be selected. In this instance, R2 and R3 do not communicate with each other and do not form any kind of virtal router.

Which command will need to be added to External_A to ensure that it will take over if serial 0/0 on External_B fails?

A. standby 1 preempt
B. standby 1 track
C. standby 1 priority 130
D. standby 1 track fastethernet 0/0
Answer: A
You can configure a router to preempt or immediately take over the active role if its priority is the highest at any time. Use the following interface configuration command to allow preemption:
Switch( config-if)# standby group preempt [delay seconds]
By default, the router can preempt another immediately, without delay. You can use the delay keyword to force it to wait for seconds before becoming active. This is usually done if there are routing protocols that need time to converge.

Refer to the exhibit. Which two problems are the most likely cause of the exhibited output?
(Choose two.)
A.spanning tree issues
B.HSRP misconfiguration
C.VRRP misconfiguration
D.physical layer issues
E.transport layer issues
Answer: B D
Each router in an HSRP group has its own unique IP address assigned to an interface. This address is used for all routing protocol and management traffic initiated by or destined to the router. In addition, each router has a common gateway IP address, the virtual router address, that is kept alive by HSRP. This address is also referred to as the HSRP address or the standby address . Clients can point to that virtual router address as their default gateway, knowing that a router always keeps that address active. Keep in mind that the actual interface address and the virtual (standby) address must be configured to be in the same IP subnet. You can assign the HSRP address with the following interface command:
Switch( config-if)# standby group ip ip-address [secondary]
When HSRP is used on an interface that has secondary IP addresses, you can add the secondary keyword so that HSRP can provide a redundant secondary gateway address.

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