Coaxial Network Cables and Connectors

10Mbps Ethernet used coaxial cables and connectors. This type of cabling is no longer common in office networks, but it is still used in some types of industrial networks because the cable is well shielded against interference.

Coaxial cabling creates a bus topology; each end of the bus must be terminated, and if any part of the bus fails, the entire network fails.

10Mbps Ethernet used RG-8 coaxial cable with a vampire tap (Thicknet) or RG-58 with a BNC connector. BNC-based networks use a T-shaped adapter to pass the signal between stations. Figure 2-4 compares network cards that use BNC, RJ-45, and AUI (vampire tap) connections.

AUI cable

Figure 2-4Combo UTP/BNC/AUI Ethernet network cards (left and right) compared with a UTP/STP-only Ethernet network card (center).

Two other types of coaxial cable are common in cable Internet, satellite Internet, and fixed wire-less Internet installations. These cables use the F-connector for direct connection between devices

RG-59—Used in older cable TV or satellite TV installations; 75ohm resistance. Also usedby the long-obsolete ARCnet LAN standard.

RG-6—Uses same connectors as RG-59, but has a larger diameter with superior shielding;used in cable TV/Internet, satellite TV/Internet, and fixed wireless Internet/TV service; 75ohm resistance.

44 CompTIA A+ Quick Reference

TCP/IP Addressing

IP addresses are considered logical because they can be assigned to the network interface card (NIC) by the network administrator. MAC addresses are permanently burned into the NIC and are, therefore, considered physical.

TCP/IP v4 Class A, B, and C Addresses

IP addresses in TCP/IP v4 are divided into three major categories that define ranges of IP address-es: Class A, Class B, and Class C. Class A is designated for large corporations, Internet service providers (ISP), and government. Class B is designated for mid-sized corporations and ISPs. Class C is designated for small offices and home offices. Each class of IP addresses uses a default subnet mask, as shown in Table 2-3.

Table 2-3 Internet Protocol v4 Classification System

By using different subnet masks, IPv4 networks are able to subdivide large networks into smaller, more efficient and easier-to-manage networks and to use classless interdomain routing (CIDR).

IPv4 Versus IPv6

Two versions of TCP/IP are in use: TCP/IP v4 and TCP/IP v6. IPv6 uses a 128-bit address, where-as IPv4 uses only 32 bits, which limits the address space to 4,294,967,296 (2³²) possible unique addresses. The newer IPv6 address space supports 2¹²⁸ (about 3.4 Ч 10³⁸) addresses.

In TCP/IP v4, an IP address has four numbers, ranging from 0 to 255, separated by dots (decimals). 192.168.7.3 is an example of an IPv4 address. The hostname is a “friendly” name that is given to a host (such as Ben-PC). TCP/IP v6 uses hexadecimal addressing, such as fe80::90ef:5273:c6aa:8f25%15.

A subnet mask is a number that the router uses to determine what part of the address is the name of the network and what part is the name of the host.

A static IP address is manually assigned to the host by the technician or network administrator. A dynamic address is assigned to the host by a server using Dynamic Host Configuration Protocol (DHCP).

127.0.0.1 is the loopback address in TCP/IP v4, which is also referred to as localhost. It is returns the packet directly back to the sending host. (Actually, the packet never really leaves the NIC.) It is used for testing. The loopback address in TCP/IP v6 is ::1.

Chapter 2: Networking 45

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