Section 5 – Implement High Availability, given a network design and a set of requirements
QUESTION NO: 36
HSRP has been configured between two Pass4sure devices. Which of the following describe reasons for deploying HSRP? (Select all that apply)
A. HSRP provides redundancy and fault tolerance
B. HSRP allows one router to automatically assume the function of the second router if the second router fails
C. HSRP allows one router to automatically assume the function of the second router if the second router starts
D. HSRP provides redundancy and load balancing
Answer: ABD
Explanation:
One way to achieve near-100 percent network uptime is to use HSRP, which 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.
By sharing an IP address and a MAC (Layer 2) address, two or more routers can act as a single “virtual” router. The members of the virtual router group continually exchange status messages.
This way, one router can assume the routing responsibility of another, should it go out of commission for either planned or unplanned reasons. Hosts continue to forward IP packets to a consistent IP and MAC address, and the changeover of devices doing the routing is transparent.
Through the use of multiple HSRP standby groups, traffic can be load balanced between the HSRP routers. For example, users on one VLAN could use one router as the primary HSRP router, and users on another VLAN can use the other HSRP router as the primary.
QUESTION NO: 37
Examine the router output above. Which two items are correct? (Choose two.)
A. The local IP address of Router A is 10.1.0.6.
B. The local IP address of Router A is 10.1.0.20.
C. If Ethernet 0/2 goesdown, the standby router will take over.
D. When Ethernet 0/3 of RouterA comes back up, the priority will become 105.
E. Router A will assume the active state if its priority is the highest.
Answer: D,E
Explanation:
HSRP election is based on a priority value (0 to 255) that is configured on each router in the group. By default, the priority is 100. The router with the highest priority value (255 is highest) becomes the active router for the group. If all router priorities are equal or set to the default value, the router with the highest IP address on the HSRP interface becomes the active router. To set the priority, use the following interface configuration command:
Switch(config-if)# standby group priority priority
When HSRP is configured on an interface, the router progresses through a series of states before becoming active. This forces a router to listen for others in a group and see where it fits into the pecking order. The HSRP state sequence is Disabled, Init, Listen, Speak, Standby, and, finally, Active.
QUESTION NO: 38
In which three HSRP states do routers send hello messages? (Choose three.)
A.standby
B.learn
C.listen
D.speak
E.active
Answer: A D E
Explanation:
When HSRP is configured on an interface, the router progresses through a series of states before becoming active. This forces a router to listen for others in a group and see where it fits into the pecking order. The HSRP state sequence is Disabled, Init, Listen, Speak, Standby, and, finally, Active.
Only the standby (second highest priority) router monitors the hello messages from the active router. By default, hellos are sent every 3 seconds. If hellos are missed for the duration of the holdtime timer (default 10 seconds, or 3 times the hello timer), the active router is presumed down.
The standby router is then clear to assume the active role. If other routers are sitting in the Listen state, the next-highest priority router is allowed to become the new standby router.
QUESTION NO: 39
What protocol specified by RFC 1256 will allow an enabled IP host a new router when a router becomes unavailable?
A. IRDP
B. SNMP
C. HSRP
D. VRRP
Answer: A
Explanation:
Some newer IP hosts use 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. The default timer values of IRDP mean that it’s not suitable for detection of failure of the first hop. The default advertisement rate is once every 7 to 10 minutes, and the default lifetime is 30 minutes.
QUESTION NO: 40
Which protocol allows for the automatic selection and simultaneous use of multiple available gateways as well as automatic failover between those gateways?
A.IRDP
B.HSRP
C.GLBP
D.VRRP
Answer: C
Explanation:
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.
