CompTIA A+ Certification Quiz Enhanced 16

What is the primary purpose of using a subnet mask in an IP network?

• To determine the protocol type. This is incorrect as the protocol type is determined by other parts of the network configuration, not the subnet mask.

• To divide a single IP network into multiple logical subnetworks. This allows different segments of a network to be identified and addressed, improving both the organization and security of the network.

• To encrypt data packets. Encryption is related to security measures and is handled by other protocols like SSL/TLS, not by subnet masking.

• To specify the router's physical address. The physical address, or MAC address, is unrelated to subnet masks, which are used for IP network segmentation.

Answer explanation

To divide a single IP network into multiple logical subnetworks

What does the subnet mask 255.255.255.0 correspond to in CIDR notation?

• /24

• /25

• /16

• /32

Answer explanation

The subnet mask 255.255.255.0 corresponds to /24 in CIDR notation because it represents 24 bits for the network portion of the IP address.

When IPv4 forwarding, if the source and destination IP addresses match, what is assumed about their network relationship?

• They are on different networks: This implies that the IP addresses belong to different network segments, which is not the case when source and destination IP addresses match.

• They are on the same subnet or network: This is correct because if the source and destination IP addresses match, it typically means they are part of the same local network or subnet, allowing for direct communication without the need for routing through an intermediary.

• They require external routing: This would be necessary if the IP addresses were on different networks, which contradicts the scenario where source and destination IP addresses match.

• They are not reachable: This would generally imply a network error or misconfiguration, which is not relevant to the scenario of matching source and destination IP addresses within the same network.

Answer explanation

When IPv4 forwarding, if the source and destination IP addresses match, it is assumed that they are on the same subnet or network.

What protocol is used to identify the MAC address associated with a destination IP address?

• ICMP: Internet Control Message Protocol, used for error messages and operational information in networks.

• ARP: Address Resolution Protocol, used to map an IP address to a MAC address that is recognized in the local network.

• TCP: Transmission Control Protocol, a core protocol of the Internet Protocol Suite, used for reliable, ordered, and error-checked delivery of bytes.

• UDP: User Datagram Protocol, used for simpler messaging transmissions that do not require the reliability and ordering of TCP.

Answer explanation

ARP protocol is used to identify the MAC address associated with a destination IP address.

What is the purpose of a router when the destination IPv4 address is on a different IP network than the source?

• To discard the packet: This is incorrect as routers are designed to route packets to their destination, not discard them unless the network is unreachable or some policy dictates so.

• To deliver the packet locally: This is incorrect because local delivery is handled by switches and hosts within the same network, not by routers which deal with traffic between different networks.

• To forward the packet to another network: This is correct. Routers are specifically used to forward packets from one network to another, using routing tables to determine the best path.

• To modify the packet's source IP address: Generally incorrect as the primary role of a router is to manage traffic between different networks, not to alter the source IP addresses, which remains the same unless NAT (Network Address Translation) is being used.

Answer explanation

To forward the packet to another network

Which of the following is NOT a range for private IPv4 addresses?

• 10.0.0.0 to 10.255.255.255

• 172.16.0.0 to 172.31.255.255

• 192.168.0.0 to 192.168.255.255

• 192.169.0.0 to 192.169.255.255

Answer explanation

The range 192.169.0.0 to 192.169.255.255 is NOT a range for private IPv4 addresses, unlike the other options provided.

What is the primary function of public IP addresses?

• To allow hosts to communicate over private LANs. Public IP addresses are not used for private LAN communication; instead, private IP addresses are used within local networks.

• To allocate addresses to customer networks by ISPs. Public IP addresses are assigned by Internet Service Providers to enable devices to communicate on the internet.

• To reserve IP addresses for private use. This is incorrect as public IP addresses are meant for external network communication, not for private use.

• To restrict internet access to certain users. Public IP addresses do not have a role in restricting internet access; this is managed through other means such as firewalls or network policies.

Answer explanation

The primary function of public IP addresses is to allocate addresses to customer networks by ISPs.

What is the default subnet mask for a Class A network in dotted decimal notation?

• 255.255.255.0

• 255.0.0.0

• 255.255.0.0

• 255.255.255.255

Answer explanation

The default subnet mask for a Class A network is 255.0.0.0, as the first octet is reserved for the network portion.

Which network prefix corresponds to a Class C default subnet mask?

• /8

• /16

• /24

• /32

Answer explanation

The network prefix that corresponds to a Class C default subnet mask is /24. In Class C, the default subnet mask is 255.255.255.0, which translates to /24 in CIDR notation.

How can a host configured with a private IP address access the Internet?

• Through a router configured with a single block of valid public addresses, using techniques like NAT (Network Address Translation) to map multiple private addresses to a public one.

• By directly connecting to the Internet without any conversion is not possible for private IP addresses as they are not routable on the Internet.

• Using a dedicated firewall only does not provide access to the Internet; it primarily secures the network by controlling incoming and outgoing traffic.

• Through a direct satellite link still requires a valid public IP address to communicate over the Internet, which private IPs do not provide.

Answer explanation

A host with a private IP address can access the Internet through a router configured with a single block of valid public addresses, which performs Network Address Translation (NAT) to allow communication between the private and public networks.