TCP/IP Questions and Answers

Answer: B

Correct answer: 2, 3 and 5

SMTP, HTTP and FTP all use TCP, because each needs delivery guaranteed and in order - a mail message, a web page and a file transfer are all useless with pieces missing. DHCP and TFTP use UDP: DHCP because a client has no address yet and must broadcast, and TFTP because it implements its own simple acknowledgement scheme and was designed to be small enough to fit in boot ROM.

Answer: B

Correct answer: Host-to-Host

The DoD model’s four layers map onto the OSI seven as follows: Application covers OSI layers 5 to 7, Host-to-Host corresponds to Transport, Internet to Network, and Network Access to Data Link and Physical. Host-to-Host is where TCP and UDP live, which is the practical way to remember it.

Answer: B

A client that sends out a DHCP Discover message in order to receive an IP address sends out a broadcast at both layer 2 and layer 3. The layer 2 broadcast is all Fs in hex, or FF:FF:FF:FF:FF:FF. The layer 3 broadcast is 255.255.255.255, which means all networks and all hosts. DHCP is connectionless, which means it uses User Datagram Protocol (UDP) at the Transport layer, also called the Host-to-Host layer.

Answer: C

Dynamic Host Configuration Protocol (DHCP) is used to provide IP information to hosts on your network. DHCP can provide a lot of information, but the most common is IP address, subnet mask, default gateway, and DNS information.

Answer: D

Correct answer: 192.168.24.43

The private ranges defined by RFC 1918 are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Only the last option falls in one. The trap is 172.15.14.36, which is outside the private block - that range begins at 172.16 and ends at 172.31, so 172.15 and 172.32 are both public.

Answer: C

Correct answer: Proxy ARP

Proxy ARP lets a router answer an ARP request on behalf of a host on another network, supplying its own MAC address so that the sender forwards the frame to the router, which then routes it onward. It exists for hosts that have no default gateway configured or that believe the whole address range is local. RARP and inverse ARP work in the opposite direction, resolving an address from a known hardware or circuit identifier.

Answer: C

Correct answer: Internet

The Internet layer of the DoD model corresponds to the Network layer of OSI, and it is where IP, ICMP, ARP and RARP operate - logical addressing and routing between networks. Host-to-Host is Transport, one layer above it, and Network Access covers the two OSI layers below.

Answer: A

Correct answer: 1, 3 and 6

DHCP, SNMP and TFTP all use UDP. Each has a reason: DHCP must broadcast before the client has an address, SNMP sends small independent polls and traps where a lost one can simply be repeated, and TFTP handles its own acknowledgements. SMTP, FTP and HTTP all need the reliable ordered stream that TCP provides.

Answer: C

Correct answer: Class C

A Class C network uses 24 bits for the network and 8 for the host, giving \( 2^8 = 256 \) addresses of which two are reserved - the all-zeros network address and the all-ones broadcast - leaving 254 usable hosts. Class B gives 65,534 and Class A gives 16,777,214, while Class D is multicast and has no host portion at all.

Answer: A

Correct answer: Application

Telnet and FTP are application layer protocols, and the Application layer is the highest in the OSI model, so that is the highest layer in use. The question is asking which layer the protocol itself occupies rather than which layers the data passes through - it passes through all seven on the way down.