Question 1

A VTP domain at your organization is made of a VTP server and three VTP clients. You want to add an additional switch to this domain. By default, what is the default mode of the new switch when it joins the domain?

Accepted Answer

By default, a new switch added to the VTP domain will be in the VTP server mode.
Key Takeaway: VTP provides a facility by which individual Cisco switches can be managed as a group for VLAN configuration purposes. Switches must be configured using three possible VTP modes. If you intend to make a switch part of a VTP management domain, each switch must be configured in one of three possible VTP modes. The VTP mode assigned to a switch will determine how the switch interacts with other VTP switches in the management domain. The three VTP modes that can be assigned to a Cisco switch include server mode, client mode, and transparent mode.

Question 2

Which of the following protocols does Frame Relay use to dynamically map DLCIs to IP addresses?

Accepted Answer

Frame Relay uses Inverse ARP to map DLCIs to IP addresses.
Key Takeaway: The locally significant DLCI must be mapped to the destination router's IP address. The two options to do this are Inverse ARP and static mapping. Inverse ARP runs by default once Frame Relay is enabled and starts working as soon as an interface is opened. If the show frame-relay map shows a dynamic mapping, it indicates that Inverse ARP was used for mapping.

Question 3

Routers R2 and R4 are directly connected on their serial1 interfaces using a DTE / DCE cable. R2 is using HDLC encapsulation and R4 is using PPP. David runs a "show interface serial1" on both of the routers. What will be the command output show?

Accepted Answer

IF you run the "show interface serial1" command on two routers using HDLC encapsulation and PPP, a message is displayed, stating, "Serial 1 is administratively down, line protocol is down."
Key Takeaway: HDLC is a layer-2 protocol used to connect point-to-point serial devices. It requires the least amount of configuration to connect these two locations. Point-to-Point Protocol, or PPP, is used for dial-up connection to the Internet. It is based on HDLC and is very similar. However, if two routers are using different encapsulation standards, the physical interface will show as "up" and the line protocol will show as "down."

Question 4

David has configured his company's ISDN link to use CHAP authentication. It worked well for a couple of weeks. However of late, the line drops very quickly after it comes up. David wants to check what the error could be. He decides to debug the CHAP process. Which command should he use?

Accepted Answer

To debug the CHAP process, David should use the debug ppp authentication command.
Key Takeaway: Whenever you want to troubleshoot an issue related to CHAP authentication, you must use a debug command. The show commands do not show anything in real time; hence, the debug command should be used. The debug PPP authentication displays the authentication process of a PPP line, including the CHAP process. This can be used to gain some insight on the problem.

Question 5

In an ISDN link, a router dials another router to establish a connection. What is the traffic that enables this dialing process called?

Accepted Answer

The traffic that enables the process of dialing from a router to another using an ISDN link is called interesting traffic.
Key Takeaway: The interesting packet activates the dialing sequence in an ISDN connection and resets the "idle-timeout" timer. Interesting traffic gets the link up and once the link is up, any traffic can cross the link. The lack of interesting traffic brings the link down.

Question 6

Which of the following RJ-45 cable types is used to connect a PC's COM port to a router or a switch console port?

Accepted Answer

Rollover cable is used to connect a PC's COM port to a router or a switch.
Key Takeaway: Rollover cable is a null-modem cable that is most commonly used to connect a computer terminal to a router's or switch's console port. It is typically flat, mostly with a light blue color. The pin outs on one end are reversed from the other, as if the wire had been rolled over, hence the name.

Question 7

Which of the following protocols use both TCP and UDP?

Accepted Answer

DNS uses both TCP and UDP for its operation.
Key Takeaway: DNS uses TCP for Zone transfer and UDP for name queries. UDP is used to exchange small information and TCP is used to exchange information larger than 512 bytes.

Question 8

What is the maximum number of hosts that can reside on a subnet with 255.255.255.192 as the subnet mask?

Accepted Answer

A maximum of 62 hosts can reside on a subnet with subnet mask 255.255.255.192.
Key Takeaway: A subnet mask of 255.255.255.192 indicates a Class C network. The last octet being 192 indicates that 2 bits among the 8 are part of the network ID. This means 6 bits are used to identify the subnet. With 6 bits, the maximum number of hosts that are a part of the subnet is 26 − 2 = 62.

Question 9

John wants to divide his organization's network into 6 subnets. He should be able to allocate a maximum of 25 hosts on each subnet. The organization's network address is 202.142.16.5. Which of the following classful subnet masks should he use?

Accepted Answer

The subnet mask that allows John to have 6 subnets with a maximum of 25 hosts per subnet is 255.255.255.224.
Key Takeaway: To divide a network such that a maximum of 6 subnets can be configured with at least 25 hosts per subnet, you should use the first 3 bits of the last octet as a part of the network ID. The other 5 bits should be used to identify the host in the subnet. Hence, the subnet mask is 255.255.255.224.

Question 10

John deletes the contents of the router's NVRAM and reboots it. Which of the following modes will the router go to when it reboots?

Accepted Answer

When you reboot the router after clearing the contents of the NVRAM, the router starts in the setup mode.
Key Takeaway: Deleting NVRAM erases all configuration settings and takes the router back to the factory setting mode. So when you reboot the router, since the router does not have a configuration file, it will automatically enter Setup mode. Setup mode presents you with a prompted dialog, called the system configuration dialog, in which you establish an initial configuration.

Question 11

David has connected two switches using two crossover cables for redundancy. STP is disabled. Which of the following is most likely to happen between the switches?

Accepted Answer

If STP is disabled between two switches that are connected using 2 cables for redundancy, broadcast storms will occur on the switched network.
Key Takeaway: A broadcast storm is a situation in which messages are broadcast on a network and each message prompts a receiving node to respond by broadcasting its own messages on the network. This in turn prompts further responses and so on. This snowball has a negative impact on network performance. Spanning Tree Protocol is a protocol that ensures a loop-free topology for a bridged LAN. So if two switches are interconnected without an STP, it forms a loop and broadcast storms occur.

Question 12

A switch receives a frame from a host on the network. The source MAC address on the frame is not listed in the MAC address table, but the destination MAC address is. What happens with the frame?

Accepted Answer

When a switch receives a frame that has a destination MAC address but not the source MAC address, it updates the MAC address table with the source MAC address.
Key Takeaway: When a switch receives a frame, it first checks if the destination address is present in its MAC table. If it is a direct route, the frame is passed to the destination host. If it is a linked route through another switch or a router, the frame is sent to the appropriate device. In case the switch does not find the source MAC address, it forwards the frame to the next link and adds the MAC information of the source in its MAC table.

Question 13

David is working as a network administrator at his organization. One of the switches on his network has a port status LED that is alternating between green and amber. What could this indicate?

Accepted Answer

If the light on the port keeps blinking between green and amber, it means that there is a problem with the switch.
Key Takeaway: When a switch port is connected, it first toggles between orange and amber. Then a stable green is established. If the light on the port keeps blinking, then it indicates there is an issue with the connection or the switch.

Question 14

Which of the following statements is true for the network shown in the figure?

Accepted Answer

The network shown in the figure has 2 broadcast domains and 9 collision domains.
Key Takeaway: Each of the hosts connected to the switch has its own collision domain and since the router is connected to 2 switches, the network has 2 broadcast domains.

Question 15

Which one of the following can significantly increase congestion on an Ethernet network?

Accepted Answer

Adding more and more hubs in to the network can significantly increase congestion on the Ethernet network.
Key Takeaway: A hub is a common connection point for devices on a network. It has multiple connection ports and is used to connect segments of a LAN. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. So if more and more hubs are added to the Ethernet network, the amount of broadcasts increase and network performance is affected adversely.

Question 16

Which of the following maps multiple private IP addresses to a single registered IP address by using different ports?

Accepted Answer

The Overloading NAT maps multiple private IP addresses to a single registered IP address using different ports.
Key Takeaway: NAT Overloading, also known as PAT or Port Address Translation, uses a single or small number of public IP addresses to map internal private IP addresses. It differentiates between sessions based on the host's port number. When a request from a client on the internal network is forwarded to its configured gateway, the gateway translates the source address and port number of the packet to use the router's public IP address. NAT mappings are stored in the router's NAT table.

Question 17

Which of the following statements regarding a switch, bridge, or a hub is NOT true?

Accepted Answer

Bridges do not forward Layer-2 broadcasts.
Key Takeaway: Both bridges and switches are Layer-2 devices designed to forward Layer-2 broadcasts. When a switch receives a frame, it sends it to ONLY that host which maps the destination MAC address on the frame. Bridges normally use two ports to bridge LANs together and switches are used to connect multiple hosts. Hence, switches typically come in 24 or 48 ports.

Question 18

Which of the following components, when added, can enable host A to ping host B?

Accepted Answer

To enable host A to ping host B, you would need to connect the two switches to a router using straight through cables.
Key Takeaway: A router is a device that forwards data packets to their destinations, based on the address specified on the packet. When a packet of data arrives at a router, its header information is scrutinized by the router. Based on the destination and source IP addresses of the packet, the router decides which neighbor it will forward it to. It chooses the route with the least cost and forwards the packet to the first router on that route. To enable pinging between 2 hosts, the switches should be connected using straight-through cables.

Question 19

David is a network administrator at his organization. Two office buildings need to be connected to use Ethernet with a bandwidth of 100 Mbps and above. David is concerned with an issue that may arise due to voltage differences between the two buildings. Which of the following media types should be used for the connection?

Accepted Answer

To avoid any issues while connecting the Ethernet segments on two different buildings which may have a voltage difference, fiber optic cable should be used.
Key Takeaway: Fiber optic cables do not carry electrical charges, so electrical issues can be avoided. Additionally, as a security feature, fiber optic cabling is immune to electronic eavesdropping.

Question 20

You want to implement VLSM for a Class C address with a point-to-point serial link. Which of the following subnet masks is most efficient?

Accepted Answer

An effective subnet mask to implement VLSM for a Class C network with a point-to-point serial link is 255.255.255.252.
Key Takeaway: Only 2 IP addresses are required for a single point-to-point link, one for the serial interface of the router at each end. Using 255.255.255.252 as the subnet mask is often used for these types of links, as no IP addresses are wasted.

Quiz 3: Networking