C. A Media Access Control (MAC) address is a unique physical address that is assigned to each network interface card. MAC addresses are "burned into" the card at the manufacturer.

D. The Presentation layer of the OSI model is responsible for converting and translating data into a form that can begin to be sent over the network. The Presentation layer provides compression and decompression as well as encryption and decryption. You can remember the Presentation layer as the translation layer.

B. The Transport layer of the OSI model contains the protocols that are responsible for resending packets that do not receive an acknowledgment from the destination address. These protocols include TCP, SPX, and other protocols.

C. The Data Link layer of the OSI model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The LLC connects the Data Link layer to the higher-level protocols such as IP at the Network layer. The MAC layer connects the Data Link layer to the physical connection and provides MAC address.

B. A network bridge operates at the Data Link layer of the OSI model. Bridges create a table using the MAC addresses of hosts that are connected to the bridge.

A. Routers operate at the Network layer using the logical addresses that are assigned at the Network layer. These include IP addresses, IPX addresses, and others.

D. NetBEUI is not a routable protocol. It is, however, a self-configuring protocol that is useful for a very small network that does not need access to the Internet.

C. An IPv4 address is a 32-bit address. It is composed of four sections of 8 bits each, called octets. Each octet is converted to decimal form for configuration purposes, but the computer uses the entire 32-bit address for communication.

B. The classful IP address of 191.222.232.254 is a class B address. All addresses in which the first octet is 128–191 are considered class B addresses.

C. If you have a class address with a default subnet mask, then the current subnet mask is

255.255.0.0. This means that you have 16 bits for networks and 16 bits for hosts. If you want to create 8 subnets, then you need 2ⁿ−2≥8. Solving for n, you can determine that you need to use the first 4 bits from the network address to create the subnets (2³−2=6, which is not enough, but 2⁴−2=14, which is more than enough). The values of the first 4 bits total 240 (128+64+32+16), so the new subnet mask is 255.255.240.0.

A, B. The valid private address ranges include the following:

• 192.168.0.0–192.168.255.255

• 172.16.0.0–172.31.255.255

• 10.0.0.0–10.255.255.255

  Only answers A and B fall into these ranges.

D. The address 169.254.2.5 is an APIPA address that was generated by the computer because it is configured to obtain an IP address from the DHCP server and a DHCP server is not available.

C. Transmission Control Protocol (TCP) is responsible for managing the three-way handshake that creates a session between two computers. TCP establishes the session by sending a short SYN message, receiving an ACK message, and then sending another short acknowledgment (ACK) message indicating that it received the acknowledgment from the other computer.

D. Simple Mail Transfer Protocol (SMTP) is responsible for sending e-mail over the Internet. SMTP is used to send e-mail to e-mail servers that use the POP3 and/or IMAP4 protocols to receive mail and make it available for users.

A. Internet Control Message Protocol (ICMP) is responsible for responding to a ping echo request with an echo reply. Ping is a tool that you can use to check general network connectivity.

B. Address Resolution Protocol (ARP) is used to resolve IP addresses to MAC addresses on a network. A computer's only truly unique physical address is the MAC address on its NIC. The MAC address must be used before packets can be delivered to a host.

C. The standard protocol used for directory services in Windows Active Directory is Lightweight Directory Access Protocol (LDAP). It is based on the X.500 standard, but it is significantly simpler.

A, C. The port numbers that are designated as well-known port numbers are those in range of 0–1,023. Ports in the range of 1,024–49,151 are designated as registered ports. Ports in the range of 49,152–65,535 are designated as dynamic or private ports.

C. A T1 line is one of the most common types of leased line used by today's businesses for connectivity to remote offices and to the Internet. It is capable of 1.544Mbps on 24 independent 64Kbps channels.

B. Point-to-Point Protocol (PPP) is the most common remote access protocol used to establish connectivity in today's remote access networks. PPP has replaced SLIP because it is more secure and flexible. PPP can be further encrypted using tunneling protocols such as PPTP and L2TP.