itself In Figure , the section that is identified by the upper box represents the 198.150.11.0 network. Data that is sent to any host on that network (198.150.11.1- 198.150.11.254) will be seen outside of the local area network as 198.159.11.0. The only time that the host numbers matter is when the data is on the local area network. The LAN that is contained in the lower box is treated the same as the upper LAN, except that its network number is 198.150.12.0. In Figure , the section that is identified by the upper box represents the 198.150.11.255 broadcast address. Data that is sent to the broadcast address will be read by all hosts on that network (198.150.11.1- 198.150.11.254). The LAN that is contained in the lower box is treated the same as the upper LAN, except that its broadcast address is 198.150.12.255. An IP address that has binary 0s in all host bit positions is reserved for the network address. In a Class A network example, 113.0.0.0 is the IP address of the network, known as the network ID, containing the host 113.1.2.3. A router uses the network IP address when it forwards data on the Internet. In a Class B network example, the address 176.10.0.0 is a network address, as shown in Figure . In a Class B network address, the first two octets are designated as the network portion. The last two octets contain 0s because those 16 bits are for host numbers and are used to identify devices that are attached to the network. The IP address, 176.10.0.0, is an example of a network address. This address is never assigned as a host address. A host address for a device on the 176.10.0.0 network might be 176.10.16.1. In this example, “176.10” is the network portion and “16.1” is the host portion. To send data to all the devices on a network, a broadcast address is needed. A broadcast occurs when a source sends data to all devices on a network. To ensure that all the other devices on the network process the broadcast, the sender must use a destination IP address that they can recognize and process. Broadcast IP addresses end with binary 1s in the entire host part of the address. In the network example, 176.10.0.0, the last 16 bits make up the host field or host part of the address. The broadcast that would be sent out to all devices on that network would include a destination address of 176.10.255.255. This is because 255 is the decimal value of an octet containing 11111111. Web Links Reserved IP Addresses http://www.nthelp.com/40/ip.htm
Content 9.2 Internet Addresses 9.2.6 Public and private IP addresses The stability of the Internet depends directly on the uniqueness of publicly used network addresses. In Figure , there is an issue with the network addressing scheme. In looking at the networks, both have a network address of 198.150.11.0. The router in this illustration will not be able to forward the data packets correctly. Duplicate network IP addresses prevent the router from performing its job of best path selection. Unique addresses are required for each device on a network. A procedure was needed to make sure that addresses were in fact unique. Originally, an organization known as the Internet Network Information Center (InterNIC) handled this procedure. InterNIC no longer exists and has been succeeded by the Internet Assigned Numbers Authority (IANA). IANA carefully manages the remaining supply of IP addresses to ensure that duplication of publicly used addresses does not occur. Duplication would cause instability in the Internet and compromise its ability to deliver datagrams to networks. Public IP addresses are unique. No two machines that connect to a public network can have the same IP address because public IP addresses are global and standardized. All machines connected to the Internet agree to conform to the system. Public IP addresses must be obtained from an Internet service provider (ISP) or a registry at some expense. With the rapid growth of the Internet, public IP addresses were beginning to run out. New addressing schemes, such as classless interdomain routing (CIDR) and IPv6 were developed to help solve the problem. CIDR and IPv6 are discussed later in the course. Private IP addresses are another solution to the problem of the impending exhaustion of public IP addresses. As mentioned, public networks require hosts to have unique IP addresses. However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique. Many private networks exist alongside public networks. However, a private network using just any address is strongly discouraged because that network might eventually be connected to the Internet. RFC 1918 sets aside three blocks of IP addresses for private, internal use. These three blocks consist of one Class A, a range of Class B addresses, and a range of Class C addresses. Addresses that fall within these ranges are not routed on the Internet backbone. Internet routers immediately discard private addresses. If addressing a nonpublic intranet, a test lab, or a home network, these private addresses can be used instead of globally unique addresses. Private IP addresses can be intermixed, as shown in the graphic, with public IP addresses. This will conserve the number of addresses used for internal connections. Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses. This translation process is referred to as Network Address Translation (NAT). A router usually is the device that performs NAT. NAT, along with CIDR and IPv6 are covered in more depth later in the curriculum. Web Links Reserved IP Addresses http://www.nthelp.com/40/ip.htm
Content 9.2 Internet Addresses 9.2.7 Introduction to subnetting Subnetting is another method of managing IP addresses. This method of dividing full network address classes into smaller pieces has prevented complete IP address exhaustion. It is impossible to cover TCP/IP without mentioning subnetting. As a system administrator it is important to understand subnetting as a means of dividing and identifying separate networks throughout the LAN. It is not always necessary to subnet a small network. However, for large or extremely large networks, subnetting is required. Subnetting a network means to use the subnet mask to divide the network and break a large network up into smaller, more efficient and manageable segments, or subnets. An example would be the U.S. telephone system which is broken into area codes, exchange codes, and local numbers. The system administrator must resolve these issues when adding and expanding the network. It is important to know how many subnets or networks are needed and how many hosts will be needed on each network. With subnetting, the network is not limited to the default Class A, B, or C network masks and there is more flexibility in the network design. Subnet addresses include the network portion, plus a subnet field and a host field. The subnet field and the host field are created from the original host portion for the entire network. The ability to decide how to divide the original host portion into the new subnet and host fields provides addressing flexibility for the network administrator. To create a subnet address, a network administrator borrows bits from the host field and designates them as the subnet field. The minimum number of bits that can be borrowed is two. When creating a subnet, where only one bit was borrowed the network number would be the .0 network. The broadcast number would then be the .255 network. The maximum number of bits that can be borrowed can be any number that leaves at least two bits remaining, for the host number. Web Links IP Address Subnetting Tutorial http://www.ralphb.net/IPSubnet/
Content 9.2 Internet Addresses 9.2.8 IPv4 versus IPv6 When TCP/IP was adopted in the 1980s, it relied on a two-level addressing scheme. At the