Q111. - (Topic 5) 

A receiving host has failed to receive all of the segments that it should acknowledge. What can the host do to improve the reliability of this communication session? 

A. decrease the window size 

B. use a different source port for the session 

C. decrease the sequence number 

D. obtain a new IP address from the DHCP server 

E. start a new session using UDP 

Answer: A Explanation: 

The Window bit in the header determines the number of segments that can be sent at a time. This is done to avoid overwhelming the destination. At the start of the session the window in small but it increases over time. The destination host can also decrease the window to slow down the flow. Hence the window is called the sliding window. When the source has sent the number of segments allowed by the window, it cannot send any further segments till an acknowledgement is received from the destination. On networks with high error rates or issues, decreasing the window size can result in more reliable transmission, as the receiver will need to acknowledge fewer segments. With a large window size, the sender will need to resend all the frames if a single one is not received by the receiver. 


Q112. - (Topic 3) 

Refer to the exhibit. 

Assume that all router interfaces are operational and correctly configured. In addition, assume that OSPF has been correctly configured on router R2. How will the default route configured on R1 affect the operation of R2? 

A. Any packet destined for a network that is not directly connected to router R2 will be dropped immediately. 

B. Any packet destined for a network that is not referenced in the routing table of router R2 will be directed to R1. R1 will then send that packet back to R2 and a routing loop will occur. 

C. Any packet destined for a network that is not directly connected to router R1 will be dropped. 

D. The networks directly connected to router R2 will not be able to communicate with the 172.16.100.0, 172.16.100.128, and 172.16.100.64 subnetworks. 

E. Any packet destined for a network that is not directly connected to router R2 will be dropped immediately because of the lack of a gateway on R1. 

Answer:

Explanation: 

First, notice that the more-specific routes will always be favored over less-specific routes regardless of the administrative distance set for a protocol. In this case, because we use OSPF for three networks (172.16.100.0 0.0.0.3, 172.16.100.64 0.0.0.63, 172.16.100.128 0.0.0.31) so the packets destined for these networks will not be affected by the default route. The default route configured on R1 “ip route 0.0.0.0 0.0.0.0 serial0/0 will send any packet whose destination network is not referenced in the routing table of router R1 to R2, it doesn’t drop anything. These routes are declared in R1 and the question says that “OSPF has been correctly configured on router R2, so network directly connected to router R2 can communicate with those three subnetworks. As said above, the default route configured on R1 will send any packet destined for a network that is not referenced in its routing table to R2; R2 in turn sends it to R1 because it is the only way and a routing loop will occur. 


Q113. - (Topic 5) 

What is the subnet broadcast address of the LAN connected to Router1? 

A. 192.168.8.15 

B. 192.168.8.31 

C. 192.168.8.63 

D. 192.168.8.127 

Answer:

Explanation: 

The IP address assigned to FA0/1 is 192.168.8.9/29, making 192.168.8.15 the broadcast address. 


Q114. - (Topic 5) 

Select two options which are security Issues which need to be modified before RouterA is used? (Choose two.) 

A. unencrypted weak password is configured to protect privilege mode 

B. inappropriate wording in banner message 

C. the virtual terminal lines have a weak password configured 

D. virtual terminal lines have a password, but it will not be used 

E. configuration supports un-secure web server access 

Answer: B,D 


Q115. - (Topic 3) 

Which two of these functions do routers perform on packets? (Choose two.) 

A. Examine the Layer 2 headers of inbound packets and use that information to determine the next hops for the packets 

B. Update the Layer 2 headers of outbound packets with the MAC addresses of the next hops 

C. Examine the Layer 3 headers of inbound packets and use that information to determine the next hops for the packets 

D. Examine the Layer 3 headers of inbound packets and use that information to determine the complete paths along which the packets will be routed to their ultimate destinations 

E. Update the Layer 3 headers of outbound packets so that the packets are properly directed to valid next hops 

F. Update the Layer 3 headers of outbound packets so that the packets are properly directed to their ultimate destinations 

Answer: B,C 

Explanation: 

This is the basic function of the router to receive incoming packets and then forward them to their required destination. This is done by reading layer 3 headers of inbound packets and update the info to layer 2 for further hopping. 


Q116. - (Topic 2) 

Refer to the exhibit. 

The MAC address table is shown in its entirety. The Ethernet frame that is shown arrives at 

the switch. 

What two operations will the switch perform when it receives this frame? (Choose two.) 

A. The switch will not forward a frame with this destination MAC address. 

B. The MAC address of 0000.00aa.aaaa will be added to the MAC Address Table. 

C. The MAC address of ffff.ffff.ffff will be added to the MAC address table. 

D. The frame will be forwarded out of all the active switch ports except for port fa0/0. 

E. The frame will be forwarded out of fa0/0 and fa0/1 only. 

F. The frame will be forwarded out of all the ports on the switch. 

Answer: B,D 

Explanation: 

If the switch already has the MAC address in its table for the destination, it will forward the frame directly to the destination port. If it was not already in its MAC table, then they frame would have been flooded out all ports except for the port that it came from. 


Q117. - (Topic 3) 

To allow or prevent load balancing to network 172.16.3.0/24, which of the following commands could be used in R2? (Choose two.) 

A. R2(config-if)#clock rate 

B. R2(config-if)#bandwidth 

C. R2(config-if)#ip ospf cost 

D. R2(config-if)#ip ospf priority 

E. R2(config-router)#distance ospf 

Answer: B,C 

Explanation: 

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.sht ml#t6 

The cost (also called metric) of an interface in OSPF is an indication of the overhead required to send packets across a certain interface. The cost of an interface is inversely proportional to the bandwidth of that interface. A higher bandwidth indicates a lower cost. There is more overhead (higher cost) and time delays involved in crossing a 56k serial line than crossing a 10M Ethernet line. The formula used to calculate the cost is: Cost = 10000 0000/bandwidth in bps For example, it will cost 10 EXP8/10 EXP7 = 10 to cross a 10M Ethernet line and will cost 10 EXP8/1544000 =64 to cross a T1 line. By default, the cost of an interface is calculated based on the bandwidth; you can force the cost of an interface with the ip ospf cost <value> interface subconfiguration mode command. 


Q118. - (Topic 1) 

Which of the following are types of flow control? (Choose three.) 

A. buffering 

B. cut-through 

C. windowing 

D. congestion avoidance 

E. load balancing 

Answer: A,C,D 

Explanation: 

During Transfer of data, a high speed computer is generating data traffic a lot faster than the network device can handle in transferring to destination, so single gateway or destination device cannot handle much amount of traffic that is called "Congestion". 

Buffering The Technie is used to control the data transfer when we have congestion, when a network device receive a data it stores in memory section and then transfer to next destination this process called "Buffering". Windowing Whereas Windowing is used for flow control by the Transport layer. Say the sender device is sending segments and the receiver device can accommodate only a fixed number of segments before it can accept more, the two devices negotiate the window size during the connection setup. This is done so that the sending device doesn't overflow the receiving device's buffer. Also the receiving device can send a single acknowledgement for the segments it has received instead of sending an acknowledgement after every segment received. Also, this window size is dynamic meaning, the devices can negotiate and change the window size in the middle of a session. So if initially the window size is three and the receiving device thinks that it can accept more number of segments in its buffer it can negotiate with the sending device and it increases it to say 5 for example. Windowing is used only by TCP since UDP doesn't use or allow flow control. 

Reference: http://www.info-it.net/cisco/ccna/exam-tips/flow-control.php 


Q119. - (Topic 3) 

Refer to the exhibit. 

If the router Cisco returns the given output and has not had its router ID set manually, what value will OSPF use as its router ID? 

A. 192.168.1.1 

B. 172.16.1.1 

C. 1.1.1.1 

D. 2.2.2.2 

Answer:

Explanation: 

If a router-id is not configured manually in the OSPF routing process the router will automatically configure a router-id determined from the highest IP address of a logical interface (loopback interface) or the highest IP address of an active interface. If more than one loopback interfaces are configured, the router will compare the IP addresses of each of the interfaces and choose the highest IP address from the loopbacks. 


Q120. - (Topic 7) 

Which dynamic routing protocol uses only the hop count to determine the best path to a destination? 

A. IGRP 

B. RIP 

C. EIGRP 

D. OSPF 

Answer: