During encapsulation, what does a protocol layer add?
A DNS aliases
B Protocol headers
C CPU instructions
D Disk sectors
Answer: B. Protocol headers. Layers add protocol-specific control information around data for transmission.
What happens during decapsulation at a receiver?
A Addresses are randomized
B Frames are rerouted
C Signals are encrypted
D Headers are removed
Answer: D. Headers are removed. The receiver processes and removes the headers added by lower layers.
What is an Ethernet frame check sequence used for?
A CRC-based error check
B Address leasing
C Path selection
D Encryption negotiation
Answer: A. CRC-based error check. The FCS uses a cyclic redundancy check to detect frame corruption.
In Ethernet II, which field identifies the payload protocol?
A DNS TTL
B TCP window
C EtherType
D TTL
Answer: C. EtherType. The EtherType field identifies the protocol carried in the Ethernet payload.
Which field guides a router’s prefix-based route match?
A Destination prefix
B Source port
C Frame checksum
D DNS alias
Answer: A. Destination prefix. Routers compare the destination address with prefixes in the routing table.
What does IPv4 limited broadcast 255.255.255.255 target?
A One DNS server
B Local link only
C All IPv6 routers
D Every Internet host
Answer: B. Local link only. The limited broadcast is intended for the local network and is not forwarded by routers.
Multicast delivery targets which group?
A Only the sender
B Every Internet host
C One chosen interface
D Selected receiver group
Answer: D. Selected receiver group. Multicast sends traffic to members of a selected receiver group.
Unicast communication normally addresses what?
A All local hosts
B Every router
C One destination host
D A receiver group
Answer: C. One destination host. Unicast traffic is addressed to one destination.
Which record type stores an IPv4 host address?
A MX record
B A record
C AAAA record
D CNAME record
Answer: B. A record. A records map a DNS name to an IPv4 address.
Which DNS record type stores an IPv6 address?
A AAAA record
B PTR record
C MX record
D A record
Answer: A. AAAA record. AAAA records map a DNS name to an IPv6 address.
What does an MX record identify?
A IPv6 prefix
B Alias target only
C Authoritative time source
D Mail exchange server
Answer: D. Mail exchange server. An MX record identifies mail exchangers for a domain.
What does a CNAME record represent?
A Canonical-name alias
B IPv4 subnet mask
C Routing metric
D Mail server priority
Answer: A. Canonical-name alias. A CNAME makes the owner name an alias for its canonical name.
Which sequence describes the common DHCPv4 startup exchange?
A Ack, Request, Discover, Offer
B Request, Ack, Offer, Discover
C Discover, Offer, Request, Ack
D Offer, Discover, Ack, Request
Answer: C. Discover, Offer, Request, Ack. The client commonly broadcasts Discover, receives Offer, sends Request, and receives Ack.
Which UDP port is used by DHCP servers?
A UDP port 53
B UDP port 67
C TCP port 80
D TCP port 22
Answer: B. UDP port 67. DHCPv4 servers receive client messages on UDP port 67.
Which TCP port is registered for SSH?
A TCP port 25
B TCP port 21
C TCP port 110
D TCP port 22
Answer: D. TCP port 22. IANA registers SSH on port 22.
Which port is conventionally used by DNS?
A Port 443
B Port 67
C Port 53
D Port 25
Answer: C. Port 53. DNS commonly uses port 53 over UDP or TCP.
What is the conventional TCP port for HTTP?
A TCP port 80
B TCP port 20
C TCP port 53
D TCP port 443
Answer: A. TCP port 80. IANA registers HTTP on TCP port 80.
Which port is conventionally assigned to HTTPS?
A Port 67
B Port 143
C Port 22
D Port 443
Answer: D. Port 443. IANA registers HTTPS on port 443.
Which protocol message does ping commonly use?
A DNS MX
B ICMP Echo
C ARP Reply
D TCP SYN
Answer: B. ICMP Echo. Traditional ping uses ICMP Echo Request and Echo Reply messages.
Why do routers decrement IPv4 TTL?
A Select an application
B Discover MAC vendors
C Limit packet lifetime
D Encrypt the payload
Answer: C. Limit packet lifetime. Each router reduces TTL so packets cannot circulate forever in a routing loop.
What does network address translation change?
A IP address mappings
B Cable frequencies
C DNS record types
D TCP sequence width
Answer: A. IP address mappings. NAT translates addresses between address realms, commonly between private and public addresses.
How can PAT let many hosts share one public address?
A Adding DNS aliases
B Transport-port multiplexing
C Using IPv6 fragments
D Changing MAC vendors
Answer: B. Transport-port multiplexing. Port Address Translation distinguishes simultaneous flows with transport-layer port mappings.
What does a VLAN create on a bridged network?
A A faster CPU core
B A public DNS zone
C Separate broadcast domains
D A longer cable
Answer: C. Separate broadcast domains. VLANs provide logical separation of bridged networks into distinct broadcast domains.
What does IEEE 802.1Q add to Ethernet frames?
A IPv6 checksums
B DNS resource records
C TCP reliability fields
D VLAN identification tags
Answer: D. VLAN identification tags. IEEE 802.1Q defines bridges and VLANs, including VLAN identification in bridged traffic.
Why is Spanning Tree Protocol used?
A Encrypt transport data
B Assign IP addresses
C Resolve domain names
D Prevent Layer-2 loops
Answer: D. Prevent Layer-2 loops. Spanning Tree prevents forwarding loops in bridged Ethernet topologies.