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IP Addressing Facts in Network Infrastructure

The following table lists the default IP addressing classes and masks:

Class	Address Range	Default Mask
A	1.0.0.0 to 126.255.255.255	255.0.0.0
B	128.0.0.0 to 191.255.255.255	255.255.0.0
C	192.0.0.0 to 223.255.255.255	255.255.255.0
D	224.0.0.0 to 239.255.255.255	(multicast addresses)
E	240.0.0.0 to 255.255.255.255	(experimental addresses)

You should also know the following address ranges that are reserved for private addresses. Use these addresses on a private network that is connected to the Internet through a network address translation (NAT) router.

• 10.0.0.0 to 10.255.255.255
• 172.16.0.0 to 172.31.255.255
• 192.168.0.0 to 192.168.255.255

Keep in mind the following facts about IP addresses:

• The first address in a range on the subnet is the subnet address. Typically, this address is not assigned to hosts.
• The last address in a range on the subnet is the broadcast address. Typically, this address is not assigned to hosts.

Use the table as a shortcut guide to subnetting. Tip: Look for patterns in the table so you can easily reproduce the table at any time.

Masked Bits	Mask Value	Number of Subnets*	Number of Hosts/Subnet**	Approximate*** Number of Hosts/Subnet
/20	255.255.240.0	N/A	4096	4000
/21	255.255.248.0	N/A	2048	2000
/22	255.255.252.0	N/A	1024	1000
/23	255.255.254.0	N/A	512	500
/24	255.255.255.0	1	256	250
/25	255.255.255.128	2	128	125
/26	255.255.255.192	4	64	60
/27	255.255.255.224	8	32	30
/28	255.255.255.240	16	16	15

*The number of subnets value is important when you need to subdivide a Class C address range into multiple subnets.
**Remember to subtract two from these numbers to arrive at the total number of addresses that can be assigned to hosts (subtract one for the subnet address and one for the broadcast address.
***Use this number as a quick estimate of the number of possible hosts.

DHCP Design Guidelines in Network Infrastructure

In a network with multiple subnets, a major concern is answering DHCP broadcast requests from all subnets. There are three ways to configure DHCP to allow clients on all subnets to get an IP address from a DHCP server.

Method	Considerations
Place a DHCP server on each subnet	The local DHCP server answers DHCP requests for its local subnet only. This solution could increase costs as you must configure a DHCP server for each subnet.
Enable BootP forwarding	Use this method if you choose to have only one DHCP server on the routed network. Place the DHCP server on the subnet with the most hosts.
Use relay agents	Configure a relay agent on each subnet that does not have a DHCP server to forward DHCP broadcasts to the remote DHCP server.

To provide fault tolerance and improve DHCP performance, you can:

• Configure split scopes. In a split scope, two DHCP servers service each subnet.
• Configure the full range of addresses in the scope on both DHCP servers.
• Exclude different ranges of addresses on each server. With both servers on the same subnet, exclude 50% of the addresses on each server. With one DHCP server on the local network, exclude addresses using the 80/20 (or 75/25) rule (exclude 80% on the remote server).
• Add relay agents to allow DHCP broadcasts to travel to remote subnets in case the local DHCP server goes down.
• Implement a DHCP cluster. Windows Server 2003 DHCP is cluster-aware. When one server goes down, the other server(s) can take over.

To decrease the time that the DHCP server takes to respond to client requests, consider the following to improve performance:

• Create a multihomed DHCP server. By doing so, the DHCP server services multiple subnets without forwarding DHCP requests through the router. A multihomed server will decrease router traffic and decrease the time it takes for clients on the remote subnet to receive their IP addresses.
• Upgrade DHCP server components. Upgrading the CPU, RAM, and network cards all affect DCHP performance, but because DHCP is a disk-intensive service, the most important upgrade is to improve disk access.
• Add additional DHCP servers. By doing so, you spread the workload between two computers.
• Modify lease lengths. Increasing the lease time means clients will not request an address as often. This reduces network traffic due to lease broadcasts, and reduces the workload on the DHCP server.

Members of the Enterprise Admins group can authorize DHCP servers (members of the Domain Admins group can administer, but not authorize, DHCP servers).

Networking With A Router

A network router is a small electronic device that allows you build a home network simply. The home router serves as the core or "centerpiece" of the network to which computers, printers and other devices can be connected. Networking with a router helps you to (for example):

• share files between computers
• share an Internet connection between computers
• share a printer
• connect your game console or other home entertainment equipment to the Internet Routers are not necessarily required to build a network. For example, you can connect two computers directly to each other with just a cable (or without wires in some cases). Home routers offer convenience and easier maintenance as your network grows.
• Related - Connecting Two Home Computers
  

Choosing a Network Router
You can choose from among several different types of home network router products. The two most common types in popular usage are the 802.11b and 802.11g WiFi models. 802.11g is the newer technology, but 802.11b routers often can do the job for an even lower cost.

Installing a Network Router
Network routers receive their power from an ordinary home electrical socket. When powered on, lights (LEDs) signify the unit is operating.

Network routers must be carefully configured when they are first installed. Like computers and other devices on the home network, routers must be set up with IP addresses. Routers also offer optional (but strongly recommended) security features.

Routers contain built-in software to enable setup. You access this software through your Web browser on any computer connected to the router.

Router

Routers are physical devices that join multiple wired or wireless networks together. Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks (as gateways do), and that the router operates at the network layer of the OSI model.
Home networkers often use an Internet Protocol (IP) wired or wireless router, IP being the most common OSI network layer protocol. An IP router such as a DSL or cable modem broadband router joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet.
By maintaining configuration information in a piece of storage called the routing table, wired or wireless routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders and receivers. Some routers allow the home networker to update the routing table from a Web browser interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit.

Repeater

Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.
Actual network devices that serve as repeaters usually have some other name. Active hubs, for example, are repeaters. Active hubs are sometimes also called "multiport repeaters," but more commonly they are just "hubs." Other types of "passive hubs" are not repeaters. In Wi-Fi, access points function as repeaters only when operating in so-called "repeater mode."
Higher-level devices in the OSI model like switches and routers generally do not incorporate the functions of a repeater. All repeaters are technically OSI physical layer devices.

OSI Model - Open Systems Interconnection Model

Definition:

The OSI model defines internetworking in terms of a vertical stack of seven layers. The upper layers of the OSI model represent software that implements network services like encryption and connection management. The lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control.
In the OSI model, data communication starts with the top layer at the sending side, travels down the OSI model stack to the bottom layer, then traveses the network connection to the bottom layer on the receiving side, and up its OSI model stack.
The OSI model was introduced in 1984. Although it was designed to be an abstract model, the OSI model remains a practical framework for today's key network technologies like Ethernet and protocols like IP.

LAN - Local Area Network

A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.
Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.
Specialized operating system software may be used to configure a local area network. For example, most flavors of Microsoft Windows provide a software package called Internet Connection Sharing (ICS) that supports controlled access to LAN resources.
The term LAN party refers to a multiplayer gaming event where participants bring their own computers and build a temporary LAN.

Switch (Network Switch)

A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.
Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.
As with hubs, Ethernet implementations of network switches are the most common. Mainstream Ethernet network switches support either 10/100 Mbps Fast Ethernet or Gigabit Ethernet (10/100/1000) standards.
Different models of network switches support differing numbers of connected devices. Most consumer-grade network switches provide either four or eight connections for Ethernet devices. Switches can be connected to each other, a so-called daisy chaining method to add progressively larger number of devices to a LAN.

Fundamental Computer Networks Concepts

In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a combination of computer hardware and computer software. Some explanations of networking found in books and tutorials are highly technical, designed for students and professionals, while others are geared more to home and business uses of computer networks.

Types of Computer Networks
Networks can be categorized in several different ways. One method defines the type of a network according to the geographic area it spans. Alternatively, networks can also be classified based on topology or on the types of protocols they support.

Types of Network Equipment
The building blocks of a home computer network include adapters, routers and/or access points. Wired (and hybrid wired/wireless) networking also involves cables of varying types. Finally, large-scale enterprise networks in particular often employ other advanced equipment for specialized communication purposes.

Ethernet
Ethernet is a physical and data link layer technology for local area networks. Homes, schools and offices around the world all commonly use Ethernet standard cables and adapters to network personal computers.

Wireless Local Area Networks
Wi-Fi is the most popular wireless communication protocol for local area networks. Private home and business networks, and public hotspots, use Wi-Fi to networks computers and other wireless devices to each other and the Internet. Bluetooth is another wireless protocol commonly used in cellular phones and computer peripherals for short range network communication.

Internet Service
The technologies used to connect to the Internet are different than those used for connecting devices on local area network. DSL, cable modem and fiber provide fixed broadband Internet service, while WiMax and LTE additionally support mobile connectivity. In geographic areas where these high-speed options are unavailable, subscribers are forced to use older cellular services, satellite or even dial-up Internet instead.

Network Routing, Switching and Bridging

Most computer networks direct messages from source to destination devices using any of three techniques called routing, switching and bridging. Routers use certain network address information contained inside messages to send them ahead to their destination (sometimes indirectly via one or more additional routers). Switches use much of the same technology as routers but typically support local area networks only. Bridging allows messages to flow between two different types of physical networks.

What is (Wireless / Computer) Networking?

In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software.

Area Networks
Networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. Local area networks (LANs), for example, typically reach across a single home, whereas wide area networks (WANs), reach across cities, states, or even across the world. The Internet is the world's largest public WAN.

Network Design

Computer networks also differ in their design. The two types of high-level network design are called client-server and peer-to-peer. Client-server networks feature centralized server computers that store email, Web pages, files and or applications. On a peer-to-peer network, conversely, all computers tend to support the same functions. Client-server networks are much more common in business and peer-to-peer networks much more common in homes.
A network topology represents its layout or structure from the point of view of data flow. In so-called bus networks, for example, all of the computers share and communicate across one common conduit, whereas in a star network, all data flows through one centralized device. Common types of network topologies include bus, star, ring and mesh.

Network Protocols

In networking, the communication language used by computer devices is called the protocol. Yet another way to classify computer networks is by the set of protocols they support. Networks often implement multiple protocols to support specific applications. Popular protocols include TCP/IP, the most common protocol found on the Internet and in home networks.

Wired vs Wireless Networking

Many of the same network protocols, like TCP/IP, work in both wired and wireless networks. Networks with Ethernet cables predominated in businesses, schools, and homes for several decades. Recently, however, wireless networking alternatives have emerged as the premier technology for building new computer networks.

Introduction to Wireless Network Security

Birth of Wireless Home Networking

It wasn’t too long ago that computers were a luxury rather than a necessity. Only the lucky and the wealthy had even one in their home and a network was something reserved for large corporations.

Fast forward a decade or so and everyone has to have their own computer. There is one for the parents (sometimes two if the parents can’t share nice) and one or more for the kids to use for homework and games. Home users have gone from no Internet access to 9600 kbps dial-up Internet access beyond 56 kbps dial-up access and are moving on to broadband connections to rival or match the T1 connections they relish at work.

As the Internet and the World Wide Web have exploded into our culture and are replacing other media forms for people to find news, weather, sports, recipes, yellow pages and a million other things, the new struggle is not only for time on the computer at home, but for time on the Internet connection.

The hardware and software vendors have come forth with a variety of solutions allowing home users to share one Internet connection among two or more computers. They all have one thing in common though- the computers must somehow be networked.

To connect your computers together has traditionally involved having some physical medium running between them. It could be phone wire, coaxial cable or the ubiquitous CAT5 cable. Recently hardware has been introduced that even lets home users network computers through the electrical wiring. But, one of the easiest and least messy ways to network computers throughout your home is to use wireless technology.

It is a fairly simple setup. The Internet connection comes in from your provider and is connected to a wireless access point or router which broadcasts the signal. You connect wireless antenna network cards to your computers to receive that signal and talk back to the wireless access point and you are in business.

The problem with having the signal broadcast though is that it is difficult to contain where that signal may travel. If it can get from upstairs to your office in the basement then it can also go that same 100 feet to your neighbors living room. Or, a hacker searching for insecure wireless connections can get into your systems from a car parked on the street.

That doesn’t mean you shouldn’t use wireless networking. You just have to be smart about it and take some basic precautions to make it more difficult for curiosity seekers to get into your personal information. The next section contains some simple steps you can take to secure your wireless network.

Security in 6 Easy Steps

1). Change the System ID:
Devices come with a default system ID called the SSID (Service Set Identifier) or ESSID (Extended Service Set Identifier). It is easy for a hacker to find out what the default identifier is for each manufacturer of wireless equipment so you need to change this to something else. Use something unique- not your name or something easily guessed.

2).Disable Identifier Broadcasting:
Announcing that you have a wireless connection to the world is an invitation for hackers. You already know you have one so you don’t need to broadcast it. Check the manual for your hardware and figure out how to disable broadcasting.

3).Enable Encryption:
WEP (Wired Equivalent Privacy) and WPA (Wi-Fi Protected Access) encrypt your data so that only the intended recipient is supposed to be able to read it. WEP has many holes and is easily cracked. 128-bit keys impact performance slightly without a significant increase in security so 40-bit (or 64-bit on some equipment) encryption is just as well. As with all security measures there are ways around it, but by using encryption you will keep the casual hackers out of your systems. If possible, you should use WPA encryption (most older equipment can be upgraded to be WPA compatible). WPA fixes the security flaws in WEP but it is still subject to DOS (denial-of-service) attacks.

4).Restrict Unnecessary Traffic:
Many wired and wireless routers have built-in firewalls. They are not the most technically advanced firewalls, but they help create one more line of defense. Read the manual for your hardware and learn how to configure your router to only allow incoming or outgoing traffic that you have approved.

5).Change the Default Administrator Password:
This is just good practice for ALL hardware and software. The default passwords are easily obtained and because so many people don’t bother to take the simple step of changing them they are usually what hackers try first. Make sure you change the default password on your wireless router / access point to something that is not easily guessed like your last name.

6).Patch and Protect Your PC’s:
As a last line of defense you should have personal firewall software such as Zone Alarm Pro and anti-virus software installed on your computer. As important as installing the anti-virus software, you must keep it up to date. New viruses are discovered daily and anti-virus software vendors generally release updates at least once a week. You also must keep up to date with patches for known security vulnerabilities. For Microsoft operating systems you can use Windows Update to try and help keep you current with patches.

What Are the Benefits of Networking?

The benefits of networking (either wired or wireless) in homes are:

file sharing -
Network file sharing between computers gives you more flexibity than using floppy drives or Zip drives. Not only can you share photos, music files, and documents, you can also use a home network to save copies of all of your important data on a different computer. Backups are one of the most critical yet overlooked tasks in home networking.

printer / peripheral sharing -
Once a home network is in place, it's easy to then set up all of the computers to share a single printer. No longer will you need to bounce from one system or another just to print out an email message. Other computer peripherals can be shared similarly such as network scanners, Web cams, and CD burners.

Internet connection sharing -
Using a home network, multiple family members can access the Internet simultaneously without having to pay an ISP for multiple accounts. You will notice the Internet connection slows down when several people share it, but broadband Internet can handle the extra load with little trouble. Sharing dial-up Internet connections works, too. Painfully slow sometimes, you will still appreciate having shared dial-up on those occasions you really need it.

multi-player games -
Many popular home computer games support LAN mode where friends and family can play together, if they have their computers networked.
Internet telephone service - So-called Voice over IP (VoIP) services allow you to make and receive phone calls through your home network across the Internet, saving you money.
home entertainment - Newer home entertainment products such as digital video recorders (DVRs) and video game consoles now support either wired or wireless home networking. Having these products integrated into your network enables online Internet gaming, video sharing and other advanced features.

Although you can realize these same benefits with a wired home network, you should carefully consider building a wireless home network instead, for the following reasons:

1. Computer mobility.
Notebook computers and other portable devices are much affordable than they were a few years ago. With a mobile computer and wireless home network, you aren't chained to a network cord and can work on the couch, on your porch, or wherever in the house is most convenient at the moment.

2. No unsightly wires.
Businesses can afford to lay cable under their floors or inside walls. But most of us don't have the time or inclination to fuss with this in our home. Unless you own one of the few newer homes pre-wired with network cable, you'll save substantial time and energy avoiding the cabling mess and going wireless.

3. Wireless is the future.
Wireless technology is clearly the future of networking. In building a wireless home network, you'll learn about the technology and be able to teach your friends and relatives. You'll also be better prepared for future advances in network technology coming in the future.

Wired vs Wireless Networking

The home networker can choose from either wireless or wired designs. Wireless networks provide more mobility to a person in and around their home, and they make especially good sense for laptop networking.

Networks with wires or cables, on the other hand, usually cost less than wireless, may perform faster and more reliably, and make good sense for desktop networking.

Choosing between wired and wireless options can be difficult, but making an informed decision here can save money and increase one's overall satisfaction with their home network.

Home Networking Tutorial

Planning a New Home Network

Before purchasing and installing equipment, determine your needs. The location of your computer(s), printer(s) and other devices you want to connect can affect your network design. Some systems may already contain built-in networking capability while others may not.
Those devices that need network capability added, probably support only certain kinds of network gear. Take care to buy compatible gear.

If you desire shared Internet access, be sure to factor this into your design. Other important factors in network design include reach and speed.

Finally, consider both present and future needs in your plan. How many computers will your network have in the next year or two? A network with just two computers can involve a very different design than a network with five, for example.

Use our interactive network advisor tool to walk you through the factors to consider when designing your home network.