Computer Networks practice questions

Answer: D) Filters traffic based on security rules

• AIncorrect. That's DNS.
• BIncorrect. It filters traffic.
• CIncorrect. That's DHCP.
• DCorrect. Allowing or blocking connections.

Answer: B) Round-trip time to a host

• AIncorrect. That isn't networking.
• BCorrect. It uses ICMP echo messages.
• CIncorrect. That's a port scan.
• DIncorrect. That's a throughput test.

Answer: D) 32

• AIncorrect. It's 32 bits.
• BIncorrect. That's IPv6.
• CIncorrect. That's a MAC address.
• DCorrect. IPv6 uses 128 bits.

Answer: D) Time taken for data to travel from source to destination

Latency is the time data takes to go from source to destination. Don't confuse it with bandwidth (data rate), bit error rate (errors) or jitter (variation in delay).

• AIncorrect. This is bandwidth (or capacity), usually given in bits per second. A link can have high bandwidth and still have high latency.
• BIncorrect. This is the bit error rate (BER), a measure of channel quality, not of delay.
• CIncorrect. This is jitter: how much the delay changes from packet to packet, not the delay itself.
• DCorrect. Latency is the end-to-end delay. It is the sum of propagation, transmission, processing and queuing delays.

Answer: D) Find the MAC address for a known IP address

• AIncorrect. That's TLS.
• BIncorrect. That's DNS.
• CIncorrect. That's DHCP.
• DCorrect. It links layer 3 to layer 2.

Answer: C) A central switch or hub

• AIncorrect. That's a bus.
• BIncorrect. That's a ring.
• CCorrect. A failed link affects only one device.
• DIncorrect. That's a daisy chain.

Answer: D) Port 443

HTTPS (HTTP over TLS) uses TCP port 443 by default. Plain HTTP uses 80, SSH uses 22 and SMTP uses 25.

• AIncorrect. TCP port 22 is the default for SSH (Secure Shell). SSH is also encrypted, but it is not HTTPS.
• BIncorrect. TCP port 80 is the default for plain, unencrypted HTTP. HTTPS uses a different well-known port.
• CIncorrect. TCP port 25 is the default for SMTP, which carries email between mail servers.
• DCorrect. HTTPS is HTTP carried over TLS, and its well-known default port is TCP 443.

Answer: B) Transport (layer 4)

• AIncorrect. That's IP.
• BCorrect. IP is at the network layer.
• CIncorrect. That's Ethernet framing.
• DIncorrect. That's HTTP and similar.

Answer: B) Maps private addresses to public addresses

• AIncorrect. That's DNS.
• BCorrect. It lets many hosts share one public IP.
• CIncorrect. That's a VPN or TLS.
• DIncorrect. MACs are set by hardware.

Answer: C) 48 bits total; 24-bit OUI

An Ethernet MAC address is 48 bits (six octets). The first 24 bits are the manufacturer's OUI and the last 24 bits identify the specific interface.

• AIncorrect. 32 bits is the length of an IPv4 address. The example has six hexadecimal octets, which is 6 × 8 = 48 bits.
• BIncorrect. The total of 48 bits is right, but the OUI is the first three octets (00:1A:2B), which is 24 bits, not 16.
• CCorrect. A MAC-48 address has six octets (48 bits). The first three octets (24 bits) form the OUI assigned to the manufacturer. The last three octets are assigned by the manufacturer to identify the specific interface.
• DIncorrect. 64 bits is the length of an EUI-64 identifier, such as an IPv6 interface identifier, not a standard Ethernet MAC address. The example has only six octets.