Local Area Network Technology: Part 5 - TCP/IP Protocol

by Jeffrey L. Carrell
Issue v1n5 - September 1997

Computers "talk" together using a set of languages called protocols. Network protocols are as different as spoken languages around the world. Now a question might be, "what's the standard protocol that all computers talk?" Unfortunately, there is not a single protocol standard that all computers use, but there are a few common ones that most computers can use. The primary protocol for connectivity on the Internet is called TCP/IP. However, many company networks may use a combination of protocols in order to more efficiently operate and control the network.


The primary protocol used on the Internet and on UNIX based networks is TCP/IP. The actual address component is IP. There has been one protocol version in use for the last 18 years, called IPv4. The maximum limit of addresses available on any one network is over 16 million, but only 127 of these networks numbers exist. However, there are some numbers that are not actually available due to limitations in the overall numbering system of IPv4. Every device connecting to an Intranet and/or the Internet must have a unique address or conflicts will occur that can cause data replies to be directed to the wrong address. In 1991the IETF formed a committee to design a new numbering system that would allow for many more numbers, while still being backward compatible to IPv4. This new IP numbering scheme is called IPv6 and is in the final stages of testing and should become a standard soon.

Any network requiring connection to the Internet needs a valid assigned IP address. The actual controlling body that assigns the valid IP addresses is called the InterNIC. Although it looks like a lot of addresses could be used, the actual limit of assigned addresses is about to be reached, this is why the IETF formed the IPng committee to design a more robust address scheme. In addition, many companies with assigned numbers are not directly connected to the Internet causing many valid addresses to not be in use directly on the Internet, thereby being a partial factor in the current address shortage. Recently, the InterNIC started assigning contiguous blocks of addresses to Internet Service Providers (ISPs), and then the ISP assigns an address to their subscribers.


IPv4 uses a 32 bit number, represented by four 8-bit bytes (or octets) in dotted decimal notation. The address is broken down into two parts: the first is called the "network" address and the second is called the "host" address. X.X.X.X is the basic layout, where each X equals a decimal number between 0-255 or hex 00-FF. There are also certain "class" numbers used and denoted in the first octet. The class designation defines how many actual host addresses are available in that specific network number. Network address 127 and all Class D addresses are reserved for specific use. The chart below indicates the numbering layout.

First Octet
Max Networks
Max Hosts per network
Subnet Mask (default)

1-127 12716777214net.host.host.host
128-191 1638465534net.net.host.host
192-223 2097152254net.net.net.host

In order for an Intranet to have more host addresses than might normally be available with the IP address assigned, an additional addressing scheme, called subnetting, can be used.

With subnets, the host portion of an IP address is partitioned into a subnet number and a 'real' host number on that subnet. The IP address is now defined as net.subnet.host. Routers outside of the Intranet do not interpret separately the subnets and host partitions of the overall IP address. Routers inside the Intranet and connected to the subnets use a 32 bit subnet mask that identifies the extension bits. In the net.subnet.host address, the subnet.host portion contains a number of bits to determine the actual address. The network administrator allocates bits within a subnet address and assigns values to the subnet and host addresses. The chart below indicates some subnet mask numbering schemes.

Number of Bits
Subnet Mask Number of SubnetsNumber of Hosts
Class B
1 232766
2 416382
3 88190
4 164094
5 322046
6 641022
7 128510
8 256254
9 512126
10 102462
11 204830
12 409614
13 81926
14 163842
Class C
1 2126
2 462
3 830
4 1614
5 326
6 642


IPv6 (formerly IPng) uses a 128 bit number, represented by eight 16-bit sections, further represented by hexadecimal numbers (0-9, A-F). The address layout is: XXXX.XXXX.XXXX.XXXX.XXXX.XXXX.XXXX. XXXX, an example might be: 5F03:2500:CFB5:D700:0000:0260:8C6C:9A9C. However, there is a shorthand feature in IPv6 that allows for leading zero's to be truncated, so the above example would actually be represented by: 5F03:2500:CFB5:D700::260:8C6C:9A9C.

Many new features and enhancements are designed into IPv6. Some of these are: enhanced addressing capabilities, namely from 32 bits (IPv4) to 128 bits; authentication and privacy capabilities, extensions to support these security features; flow labeling capability, a new quality-of-service (QOS) feature providing for special handling of data. Although the capabilities of IPv6 will be significantly better than the present IPv4, there are many tests still in process and many products will require extensive software rewrites in order to allow IPv6 to interoperate with IPv4. Router software, DNS applications, client protocol stacks, TCP/IP applications, will all be required to update to IPv6 as well as a general understanding of the IPv6 protocol addressing scheme by network administrators will be required.

There is a test network available on the Internet, called the 6bone, which vendors and ISPs are currently in process of conducting stress tests. Although the IPv6 protocol is being tested, it may be a year or two before most of the products are commercially available. Before a company tries to implement IPv6, it is highly recommended that they acquire the IPv6 products and connect to the 6bone and participate in the IPv6 tests, to ensure proper operation before introducing the products in their production Intranet.


IETF Internet Engineering Task Force

InterNIC Internet Network Information Center

IP Internet Protocol

IPng IP Next Generation

IPv4 IP version 4

IPv6 IP version 6

ISP Internet Service Provider

NIC Network Interface Card

TCP Transmission Control Protocol

TCP/IP Internet Protocol/Transmission Control Protocol

Copyright © 1997 Jeffrey L. Carrell. All Rights Reserved.

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