A /26 IPv4 subnet has how many usable host addresses?
A 32 hosts
B 30 hosts
C 64 hosts
D 62 hosts
Answer: D. 62 hosts. A /26 has 64 total addresses; the network and broadcast addresses leave 62 usable host addresses.
How many /27 subnets fit inside one /24?
A 16 subnets
B 8 subnets
C 4 subnets
D 2 subnets
Answer: B. 8 subnets. The prefix grows by three bits, producing 2^3, or eight, equal subnets.
Which TCP flag starts the usual connection handshake?
A ACK
B FIN
C SYN
D RST
Answer: C. SYN. The active opener sends a SYN to begin a TCP connection.
What does a server normally send after receiving a valid SYN?
A SYN-ACK
B RST-ACK
C Data-ACK
D FIN-ACK
Answer: A. SYN-ACK. The responding TCP endpoint acknowledges the SYN and sends its own SYN.
Which segment normally completes the three-way handshake?
A Reset segment
B Second SYN
C First FIN
D Third ACK
Answer: D. Third ACK. The initiator sends an ACK to acknowledge the peer’s SYN.
What do TCP sequence numbers track?
A Router hop counts
B Ethernet port numbers
C Byte-stream positions
D DNS cache age
Answer: C. Byte-stream positions. TCP sequence numbers identify positions in the byte stream.
What does TCP’s advertised receive window support?
A DNS authentication
B Receiver-side flow control
C Route aggregation
D Link discovery
Answer: B. Receiver-side flow control. The receive window limits outstanding data according to receiver capacity.
What does TCP congestion window limit?
A Outstanding network data
B Ethernet address count
C DNS response length
D Local file size
Answer: A. Outstanding network data. The sender’s congestion window limits unacknowledged data injected into the network.
What is retransmission intended to recover?
A Expired DNS names
B Changed MAC addresses
C Lost TCP data
D Unused IP prefixes
Answer: C. Lost TCP data. TCP retransmits data that appears lost so reliable delivery can continue.
Which routing approach does OSPF use?
A Flood-only bridging
B Name-server recursion
C Distance-vector routing
D Link-state routing
Answer: D. Link-state routing. OSPF is a link-state or shortest-path-first routing protocol.
Which metric does RIP use for route distance?
A Hop count
B Signal frequency
C Frame length
D TCP window
Answer: A. Hop count. RIP uses hop count as its route metric, with a finite maximum.
BGP primarily exchanges routes between which entities?
A Ethernet ports
B Autonomous systems
C Process threads
D DNS labels
Answer: B. Autonomous systems. BGP exchanges reachability information among autonomous systems.
What does a DNS record’s TTL govern?
A Ethernet frame size
B TCP connection lifetime
C Cache lifetime
D Router interface speed
Answer: C. Cache lifetime. TTL indicates how long a DNS record may be cached.
A recursive DNS resolver does what for its client?
A Chooses a TCP window
B Assigns a DHCP lease
C Forwards Ethernet bits
D Follows referrals for it
Answer: D. Follows referrals for it. A recursive resolver obtains an answer by querying other DNS servers as needed.
What does an authoritative DNS server provide?
A Zone’s authoritative records
B A default gateway
C A switch port map
D A TCP retransmission
Answer: A. Zone’s authoritative records. Authoritative servers provide DNS data for the zones they serve.
Overlapping routes match a destination; which one is preferred?
A Lowest source port
B Newest DNS alias
C Longest matching prefix
D Shortest route name
Answer: C. Longest matching prefix. CIDR forwarding prefers the most specific matching prefix.
After comparing routes, what does OSPF’s path cost help select?
A Largest frame
B Lowest-cost path
C Highest-hop path
D Nearest DNS server
Answer: B. Lowest-cost path. OSPF’s shortest-path calculation selects a route with the lowest accumulated cost.
Which MAC address does a learning switch record from an incoming frame?
A Destination IP address
B DNS owner name
C TCP source port
D Source MAC address
Answer: D. Source MAC address. A learning bridge records the source MAC address on the port where the frame arrived.
How is the root bridge chosen in classic spanning tree?
A Lowest bridge ID
B Newest MAC entry
C Highest port number
D Shortest frame
Answer: A. Lowest bridge ID. The bridge with the lowest bridge ID becomes the root bridge.
How is an ARP request sent on Ethernet when the target MAC is unknown?
A TCP SYN packet
B IPv6 multicast only
C Local broadcast frame
D Unicast to DNS
Answer: C. Local broadcast frame. An Ethernet ARP request is normally broadcast on the local link.
What does TCP MSS specify?
A Maximum route length
B Maximum segment payload
C Minimum DNS TTL
D Maximum MAC address
Answer: B. Maximum segment payload. MSS is the maximum TCP data size accepted in one segment, excluding TCP and IP headers.
What does IPv4 prefix 0.0.0.0/0 represent?
A Default route
B Loopback route
C Host-specific route
D Multicast route
Answer: A. Default route. A /0 route matches any IPv4 destination when no more-specific route applies.
Which data does the TCP checksum cover?
A DNS question only
B Ethernet frame only
C IP header only
D Segment and pseudoheader
Answer: D. Segment and pseudoheader. TCP’s checksum covers the TCP header and data plus a pseudoheader from IP.
Which ICMP messages does traditional ping exchange?
A Redirect and Reset
B Echo Request and Reply
C Discover and Offer
D SYN and ACK
Answer: B. Echo Request and Reply. Ping commonly sends Echo Requests and receives Echo Replies.
What does ICMP Destination Unreachable report?
A Delivery failure condition
B New address lease
C Successful delivery
D VLAN membership
Answer: A. Delivery failure condition. It reports that a packet could not be delivered for a specified network or host reason.