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IP Routing


Here you will find answers to IP Routing Questions
Question 1
Refer to the exhibit. In this network, R1 has been configured to advertise a summary route, 192.168.0.0/22, to R2. R2 has been configured to advertise a summary route. 192.168.0.0/21. to R1. Both routers have been configured to remove the discard route (the route to null created when a summary route is configured) by setting the administrative distance of the discard route to 255.
loop.jpg
What will happen if R1 receives a packet destined to 192.168.3.1?
A.    The packet will loop between R1 and R2
B.    It is not possible to set the administrative distance on a summary to 255
C.    The packet will be forwarded to R2, where it will be routed to null0
D.    The packet will be dropped by R1, since there is no route to 192.168.3.1.

Answer: A
Question 2
While troubleshooting a network, you need to verify the liveness of hosts in the subnet 192.168.1.64/26. All of the hosts are able to reply to ping requests. How would you confirm the existing nodes using one single command?
A. ping 192.168.1.255
B. ping with sweep option
C. ping 192.168.1.127
D. ping 192.168.1.64
E. ping with broadcast option

Answer: C
Explanation
The 192.168.1.27 is the broadcast address of the 192.168.1.64/26 sub-network so by sending a ping request to this address all the hosts in this subnet will reply (to the broadcast address). But it is not quite right nowadays as all the Cisco’s routers which have  IOS version 12.0 or above will simply drop these pings. If you wish to test this function then you have to turn on the “ip directed-broadcast” function (which is disabled by default from version 12.0).
The purpose of the “ip directed-broadcast” command is to enable forwarding of directed broadcasts. When this is turned on for an interface, the interface will respond to broadcast messages that are sent to its subnet. Cisco introduced this command in IOS version 10 (and it is enabled by default) but they soon realized this command was being exploited in denial of service attacks and disabled it from version 12.0.
As you can guess, a ping to the broadcast address requires all hosts in that subnet to reply and it consumes much traffic if many are sent. A type of this attack is “smurf attack”, in which the attacker tries to borrow the victim’s IP address as the source address and sends ICMP packets to the broadcast address of the network. When all the hosts in that subnet hear the ICMP request, they will reply to the computer which the attacker borrowed the IP address from.
You can try this function by enabling “ip directed-broadcast” command in interface mode. Then from the directly connected router issue the ping to the broadcast address of that subnet (or ping 255.255.255.255).
Question 3
Which mechanism can you use to achieve sub-second failover for link failure detection when a switched Ethernet media is used and loss of signal is not supported by the link provider?
A. OSPF standard hellos
B. Cisco Discovery Protocol link detection
C. Bidirectional Forwarding Detection
D. Fast Link Pulse
E. autonegotiation

Answer: C
Explanation
BFD is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable
Question 4
Half of your network uses RIPv2 and the other half runs OSPF. The networks do not communicate with each other. Which two of these factors describe the impact of activating EIGRP over each separate part? (Choose two)
A. EIGRP will not be accepted when configured on the actual RIPv2 routers.
B. OSPF will no longer be used in the routing table, because you only have EIGRP internal routes running.
C. OSPF will no longer be used in the routing table, because you only have EIGRP external routes running.
D. RIPv2 will populate its RIP database but not its routing table, because you only have EIGRP external routes running.
E. RIPv2 will populate its RIP database but not its routing table, because you only have EIGRP internal routes running.
F. OSPF database will have RIPv2 routes.

Answer: B E
Question 4
Based on the exhibit presented. What will be the objective of this route map when applied to traffic passing through a router?
route-map direct-traffic permit 10
match ip address 100
set next-hop 10.1.1.1
…………….
access-list 100 permit ip any host 10.1.14.25
access-list 100 permit ip 10.2.0.0 0.0.255.255 any
A. Take any packet sourced from any address in the 10.2.0.0/16 network or destined to 10.1.14.25 and set the next hop to 10.1.1.1
B. Take any packet sourced from any address in the 10.2.0.0/16 network and destined to 10.1.14.25 and set the next hop to 10.1.1.1
C. Nothing; extended access lists are not allowed in route maps used for policy-based routing
D. Drop any packet sourced from 10.2.0.0/16

Answer: A
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