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642-813 Q&A – Implement High Availability (16-20)

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

QUESTION NO: 16
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.Load sharing with HSRP is achieved by creating HSRP groups on the HSRP routers.
C.Routers configured for HSRP must belong to only one group per HSRP interface.
D.Routers configured for HSRP can belong to multiple groups and multiple VLANs.
E.All routers configured for HSRP load balancing must be configured with the same priority.
Answer: B D

Explanation:
HSRP is a Cisco-proprietary protocol developed to allow several routers (or multilayer switches) to appear as a single gateway address. RFC 2281 describes this protocol in more detail. Basically, each of the routers that provides redundancy for a given gateway address is assigned to a common HSRP group. One router is elected as the primary, or active, HSRP router, another is elected as the standby HSRP router, and all the others remain in the listen HSRP state. The routers exchange HSRP hello messages at regular intervals, so they can remain aware of each other’s existence, as well as that of the active router.
An HSRP group can be assigned an arbitrary group number, from 0 to 255. If you configure HSRP groups on several VLAN interfaces, it can be handy to make the group number the same as the VLAN number. However, most Catalyst switches support only up to 16 unique HSRP group numbers. If you have more than 16 VLANs, you will quickly run out of group numbers. An alternative is to make the group number the same (that is, 1) for every VLAN interface. This is perfectly valid because the HSRP groups are only locally significant on an interface. HSRP Group 1 on interface VLAN 10 is unique from HSRP Group 1 on interface VLAN 11.

QUESTION NO: 17
With route processor redundancy (RPR+), the redundant supervisor engine is fully initialized and configured, which shortens the switchover time if the active supervisor engine fails. Which three statements are true about the RPR + operations when the redundant supervisor engine switched over the failed primary supervisor engine? (Choose three.)
A.The Forwarding Information Base (FIB) tables are maintained during the switchover. As a result, routed traffic continues without any interruption when the failover occurs.
B.The Forwarding Information Base (FIB) tables are cleared on a switchover. As a result, routed traffic is interrupted until route tables reconverge.
C.Static IP routes are maintained across a switchover because they are configured from entries in the configuration file.
D.Static IP routes are cleared across a switchover and recreated from entries in the configuration file on the redundant supervisor engine.
E.Information about dynamic routing states, maintained on the active supervisor engine, is synchronized to the redundant supervisor engine and is transferred during the switchover.
F.Information about dynamic routing states, maintained on the active supervisor engine, is not synchronized to the redundant supervisor engine and is lost on switchover.
Answer: B C F

QUESTION NO: 18
Routers R1 and R2 are configured for HSRP as shown below:

Router R1:
interface ethernet 0
ip address 20.6.2.1 255.255.255.0
standby 35 ip 20.6.2.21
standby 35 priority 100
interface ethernet 1
ip address 20.6.1.1.2 255.255.255.0
standby 34 ip 20.6.1.21

Router R2:
interface ethernet 0
ip address 20.6.2.2 255.255.255.0
standby 35 ip 20.6.2.21
interface ethernet 1
ip address 20.6.1.1.1 255.255.255.0
standby 34 ip 20.6.1.21
standby 34 priority 100

You have configured the routers R1 & R2 with HSRP. While debugging router R2 you notice very frequent HSRP group state transitions. What is the most likely cause of this?
A. physical layer issues
B. no spanning tree loops
C. use of non-default HSRP timers
D. failure to set the command standby 35 preempt
Answer: A
Explanation:
R2 is not able to from the standby state to reach the active state. This could be caused by missing HSRP hello messages. There are several possible causes for HSRP packets to get lost between the peers. The most common problems are Physical Layer Problems or excessive network traffic caused by Spanning-Tree Issues.
Note:
Hot Standby Routing Protocol (HSRP) is a Cisco proprietary protocol used for allowing redundant connections. It can keep core connectivity if the primary routing process fails.
HSRP defines six states in which an HSRP router may run: initial, learn, listen, speak, standby, and active.
Incorrect Answers:
B: Spanning tree loops does not affect this problem.
C: Not a likely cause. Besides, in the example here the default values were indeed used.

QUESTION NO: 19
Refer to the exhibit. Which two statements are true about the output from the show standby vlan 50 command?(Choose two.)

18
A. multipoint control unit (MCU) Catalyst_A.
B. 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.
C. Hosts using the default gateway address of 192.168.1.2 will have their traffic sent to
Catalyst_A.
D. Catalyst_A is load sharing traffic in VLAN 50.
Answer: C,D
Explanation:
HSRP uses a priority scheme to determine which HSRP-configured router is to be the default active router. To configure a router as the active router, you assign it a priority that is higher than the priority of all the other HSRP-configured routers. The default priority is 100, so if you configure just one router to have a higher priority, that router will be the default active router.
HSRP works by the exchange of multicast messages that advertise priority among HSRPconfigured routers. When the active router fails to send a hello message within a configurable period of time, the standby router with the highest priority becomes the active router. The transition of packet- forwarding functions between routers is completely transparent to all hosts on the network.

QUESTION NO: 20
To protect against first-hop router failure, four protocols were developed to ensure IP routing redundancy. Which of the following are they? (Select four)
A. HSRP
B. IRDP
C. ICMP
D. VRRP
E. MSTP
F. GLBP
Answer: A,B,D,F
Explanation:
A: HSRP is the Hot Standby Routing Protocol, which is the Cisco proprietary method for automatic failover and provides for redundant default gateways for hosts.
B: Some newer IP hosts use the ICMP Router Discovery Protocol (IRDP) (RFC 1256) to find a new router when a route becomes unavailable. A host that runs IRDP listens for hello multicast messages from its configured router and uses an alternate router when it no longer receives those hello messages.
D: VRRP is the Virtual Router Redundancy Protocol, which is similar in many ways to HSRP.
One key difference is that VRRP is standards based, where HSRP is Cisco developed.
F: Gateway Load Balancing Protocol (GLBP) protects data traffic from a failed router or circuit, like Hot Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP), while allowing packet load sharing between a group of redundant routers.

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