8.6.2 Module Quiz – Network Layer Answers
1. Which command can be used on a Windows host to display the routing table?
- netstat -s
- show ip route
- netstat -r
- tracert
Explanation: On a Windows host, either the route print or netstat -r commands can be used to display the host routing table. The show ip route command is used on a router to display its routing table. The netstat –s command is used to display per-protocol statistics. The tracert command is used to display the path that a packet travels to its destination.
2. What information is added during encapsulation at OSI Layer 3?
- source and destination MAC
- source and destination application protocol
- source and destination port number
- source and destination IP address
Explanation: IP is a Layer 3 protocol. Layer 3 devices can open the Layer 3 header to inspect the Layer 3 header which contains IP-related information including the source and destination IP addresses.
3. How does the network layer use the MTU value?
- The network layer depends on the higher level layers to determine the MTU.
- The network layer depends on the data link layer to set the MTU, and adjusts the speed of transmission to accommodate it.
- The MTU is passed to the network layer by the data link layer.
- To increase speed of delivery, the network layer ignores the MTU.
Explanation: The data link layer indicates to the network layer the MTU for the medium that is being used. The network layer uses that information to determine how large the packet can be when it is forwarded. When packets are received on one medium and forwarded on a medium with a smaller MTU, the network layer device can fragment the packet to accommodate the smaller size.
4. Which characteristic describes an IPv6 enhancement over IPv4?
- IPv6 addresses are based on 128-bit flat addressing as opposed to IPv4 which is based on 32-bit hierarchical addressing.
- The IPv6 header is simpler than the IPv4 header is, which improves packet handling.
- Both IPv4 and IPv6 support authentication, but only IPv6 supports privacy capabilities.
- The IPv6 address space is four times bigger than the IPv4 address space.
Explanation: IPv6 addresses are based on 128-bit hierarchical addressing, and the IPv6 header has been simplified with fewer fields, improving packet handling. IPv6 natively supports authentication and privacy capabilities as opposed to IPv4 that needs additional features to support those. The IPv6 address space is many times bigger than IPv4 address space.
5. When a connectionless protocol is in use at a lower layer of the OSI model, how is missing data detected and retransmitted if necessary?
- Connectionless acknowledgements are used to request retransmission.
- Upper-layer connection-oriented protocols keep track of the data received and can request retransmission from the upper-level protocols on the sending host.
- Network layer IP protocols manage the communication sessions if connection-oriented transport services are not available.
- The best-effort delivery process guarantees that all packets that are sent are received.
Explanation: When connectionless protocols are in use at a lower layer of the OSI model, upper-level protocols may need to work together on the sending and receiving hosts to account for and retransmit lost data. In some cases, this is not necessary, because for some applications a certain amount of data loss is tolerable.
6. What was the reason for the creation and implementation of IPv6?
- to make reading a 32-bit address easier
- to relieve IPv4 address depletion
- to provide more address space in the Internet Names Registry
- to allow NAT support for private addressing
Explanation: IPv4 addressing space is exhausted by the rapid growth of the Internet and the devices connected to the Internet. IPv6 expands the IP addressing space by increasing the address length from the 32 bits to 128 bits, which should provide sufficient addresses for future Internet growth needs for many years to come.
7. Which statement accurately describes a characteristic of IPv4?
- All IPv4 addresses are assignable to hosts.
- IPv4 has a 32-bit address space.
- An IPv4 header has fewer fields than an IPv6 header has.
- IPv4 natively supports IPsec.
Explanation: IPv4 has a 32-bit address space, providing 4,294,967,296 unique addresses, but only 3.7 billion are assignable, a limit due to address reservation for multicasting and testing. IPv4 does not provide native support for IPsec. IPv6 has a simplified header with fewer fields than IPv4 has.
8. Which field in an IPv4 packet header will typically stay the same during its transmission?
- Flag
- Time-to-Live
- Packet Length
- Destination Address
Explanation: The value in the Destination Address field in an IPv4 header will stay the same during its transmission. The other options might change during its transmission.
9. When a router receives a packet, what information must be examined in order for the packet to be forwarded to a remote destination?
- destination MAC address
- source IP address
- destination IP address
- source MAC address
Explanation: When a router receives a packet, it examines the destination address of the packet and uses the routing table to search for the best path to that network.
10. Which field in an IPv6 packet is used by the router to determine if a packet has expired and should be dropped?
- TTL
- Hop Limit
- Address Unreachable
- No Route to Destination
Explanation: ICMPv6, like IPv4, sends a Time Exceeded message if the router cannot forward an IPv6 packet because the packet has expired. However, the IPv6 packet does not have a TTL field. Instead, it uses the Hop Limit field to determine if the packet has expired.
11. Which information is used by routers to forward a data packet toward its destination?
- source IP address
- destination IP address
- source data-link address
- destination data-link address
Explanation: The destination IP address is the IP address for the receiving device. This IP address is used by routers to forward the packet to its destination.
12. A computer has to send a packet to a destination host in the same LAN. How will the packet be sent?
- The packet will be sent to the default gateway first, and then, depending on the response from the gateway, it may be sent to the destination host.
- The packet will be sent directly to the destination host.
- The packet will first be sent to the default gateway, and then from the default gateway it will be sent directly to the destination host.
- The packet will be sent only to the default gateway.
Explanation: If the destination host is in the same LAN as the source host, there is no need for a default gateway. A default gateway is needed if a packet needs to be sent outside the LAN.
13. A router receives a packet from the Gigabit 0/0 interface and determines that the packet needs to be forwarded out the Gigabit 0/1 interface. What will the router do next?
- route the packet out the Gigabit 0/1 interface
- create a new Layer 2 Ethernet frame to be sent to the destination
- look into the ARP cache to determine the destination IP address
- look into the routing table to determine if the destination network is in the routing table
Explanation: Once a router receives a packet and looks inside the header to determine the destination network, the router compares the destination network to the routing table to determine if the packet is to be routed or dropped. If routed, the router attaches a new Layer 2 header based on the technology that is used by the outgoing port that is used. The packet is then routed out the destination port as designated by the routing table. The ARP cache is used to match an IP address with a MAC address.
14. Which IPv4 address can a host use to ping the loopback interface?
- 126.0.0.1
- 127.0.0.0
- 126.0.0.0
- 127.0.0.1
Explanation: A host can ping the loopback interface by sending a packet to a special IPv4 address within the network 127.0.0.0/8.