Configuring Windows 7 (Training Kit) - Part 34 potx

This can be a hardware router, a server that is configured as a router, or the computer or wireless router through which the other computers in a small office/home office SOHO network ac

So what identifies the computer and what identifies the subnet? To discover this, we need

to look at the next value, the subnet mask Subnet masks are most peculiar numbers They

represent binary numbers that consist of all ones followed by all zeros For example:

255.255.255.0 is the binary number 11111111 11111111 11111111 00000000.

The actual value of this number is irrelevant What matters is the number of ones and

zeros A one says that the corresponding bit in the IPv4 address is a network address bit

A zero says that the corresponding bit in the IPv4 address is a computer or host address bit

In the example given, the last 8 bits of the subnet mask are all zero So the host address is

the final octet of the subnet address, or 143 The network address of the subnet is 10 16 10 0

Because hosts are defined by a single octet in this example, the 10 16 10 0 subnet contains

254 host addresses The first IPv4 address in the subnet is 10 16 10 1 The last is 10 16 10 254

The number 10 16 10 0 identifies the subnet and is called the subnet address The number

10 16 10 255 is called the broadcast address and is used when a packet needs to be sent to

every host on a subnet

Subnetting and Supernetting

You can split a subnet into smaller subnets by adding ones to the end of the ones in the

subnet mask If you have two (or more) suitable contiguous subnets, you can merge them into

a single subnet by changing one or more ones at the end of the ones in the subnet masks to

zeros These techniques are known as subnetting and supernetting, respectively

If an organization has a significant number of computers on its network (say over 100—this

number varies depending on the type, volume, and pattern of traffic on the network—or if it

has several geographic locations, the organization probably creates several subnets If a subnet

contains too many computers and other devices, it tends to slow down because there is a greater

chance of two computers trying to put data onto the network simultaneously and causing

a collision Dividing a network into several subnets reduces the likelihood of such collisions

At the router that connects to the Internet, however, the organization uses supernetting

to combine (or summarize) the subnets so that they can be defined with a single network

address that will be translated to a public address on the Internet Public addresses and

address translation are discussed later in this lesson

More Info SUBNettINg aND SUperNettINg

For more information about supernetting and subnetting, and about CIDR and VLSM

technologies, see http://support.microsoft.com/kb/164015

note CIDr NOtatION

Because the subnet mask 255.255.255.0 consists of 24 ones followed by 8 zeros, you

can also write it as /24 A subnet with a network address 192.168.0.0 and a subnet mask

255.255.255.0 (for example) is then designated 192.168.0.0/24 This is sometimes called

CIDR notation A subnet mask with 25 ones followed by 7 zeros is a /25 subnet mask In

dotted decimal, this would be 255.255.255.128.

The final value shown in Figure 6-1 is the default gateway This is the IPv4 address of the

router connection on the same subnet as the IPv4 address of the host computer If an IPv4 packet has a destination address of a different subnet, it is routed through other subnets via the router until it finds the destination it is looking for If you browse to a Web site, for example, you need to send data to the Web server for that site, which has an IPv4 address somewhere on the Internet

Put simply, some packets need to get out of your subnet and go to another network (for example, the Internet) Your computer sends these packets to a routing device This can be

a hardware router, a server that is configured as a router, or the computer or wireless router through which the other computers in a small office/home office (SOHO) network access the Internet The default gateway is the address within the subnet of the routing device (which has at least one more IPv4 address on another subnet) It is where outgoing packets leave the subnet It is also where incoming packets from other networks enter the subnet

quick Check

1. What is the binary number 00001010 11110000 10101010 01000000 in dotted decimal notation?

2. Are the IPv4 addresses 192.168.1.200 and 192.168.1.24 on the same subnet? Both have a subnet mask of 255.255.255.0.

3. Is 10.0.0.130 a valid IPv4 address on the 10.0.0.0/25 subnet?

quick Check answers

1. 10.240.170.64.

2. The subnet mask specifies that the final octet holds the host address Therefore the first three octets hold the subnet’s network address In both cases, this is 192.168.1.0, so the computers are on the same subnet.

3. No The /25 subnet mask specifies 25 ones and therefore 32 – 25 = 7 zeros Zeros denote host address Therefore, the host address is from 0000001 to 1111110 binary (0000000 is the network address and 111111 the broadcast address) In decimal, this is 1 to 126 So the valid IPv4 addresses on the network are 10.0.0.1

to 10.0.0.126 10.0.0.130 is not in this range and therefore is not valid on this subnet It is an address on another subnet (for example, 10.0.0.128/25).

Network Services

IPv4 configuration and operation relies on a number of network services In an enterprise environment, these services (apart from APIPA) are implemented on servers However, on a small network, DHCP and DNS services can be provided by a client running ICS or by a WAP Services associated with IPv4 include the following:

n DhCp Assigns IPv4 addresses to hosts that are set to receive their configurations

automatically It assigns IPv4 addresses from one or more scopes and handles IPv4

address leasing and renewal Exclusion ranges can be defined for non-DHCP-enabled

hosts, and static assignments can be made to specific media access control (MAC)

addresses DHCP can also specify the IPv4 address of the default gateway(s) and DNS

server(s)

n DNS Resolves both local host names and fully qualified domain names (FQDNs)—for

example, http://www.contoso.internal—to IPv4 addresses (and vice versa) A local DNS

server can perform this function on its own subnet For example, if you enter ping

canberra in the Command Prompt window, DNS resolves the computer name Canberra

to its IPv4 address DNS also works over the Internet to resolve the FQDNs of remote

Web sites to their IPv4 addresses DNS provides a connection-specific DNS suffix for

e-mail addresses If you had an e-mail server (for example, a server running Microsoft

Exchange Server) on your network, the connection-specific DNS suffix would be the

section of the e-mail address after the @ symbol (for example, don hall@tailspintoys

com) The Dynamic Domain Name Service (DDNS) uses the concept of a dynamic

database and enables dynamic updates

More Info INterNaL VS eXterNaL reSOLUtION

If you need to resolve a computer name on your internal network to an IPv4 address

(for example, if you entered ping canberra in the Command Prompt window), then

the DNS service on your WAP or ICS computer will provide the IPv4 address that

corresponds to the computer name If, on the other hand, you needed to resolve an

FQDN on the Internet (for example if you entered http://www.contoso.com in your

browser), then that FQDN is resolved over the Internet FQDNs are resolved over the

Internet using a DNS server hierarchy and an iterative process It is unlikely that the

70-680 examination will test your knowledge of iterative DNS queries However, if you

want to know more about this topic out of professional interest, see http://technet.

microsoft.com/en-us/library/cc775637.aspx.

n apIpa Configures an internal private network when DHCP is not provided If you

have a network with no connection to any other network and you want the computers

on that network to see one another, you can connect them by using an Ethernet switch

and allow them to configure themselves without requiring DHCP services APIPA

configures a computer’s IPv4 settings with an IPv4 address in the range 169 254 0 1

through 169 254 255 254 and a subnet mask of 255 255 0 0 APIPA does not configure

a default gateway because an APIPA-configured network does not send IPv4 packets

to, or receive them from, any other network

n Nat Allows many devices on a private network to gain access to the Internet

through one public IPv4 address NAT translates between private IPv4 addresses used

internally in a local network and public addresses used on the Internet When you

send a request to the Internet—for example, by typing a Uniform Resource Locator

(URL) into a browser—the information that the request returns (the Web page) needs

to find its way back to your computer, which has an internal IPv4 address on your local area network (LAN) Typically, your ISP allocates only one public IPv4 address that all the computers on your LAN share when accessing the Internet NAT deals with this situation and ensures that IPv4 packets from the Internet reach the correct LAN destinations

More Info NetWOrK aDDreSS traNSLatION

For more information about NAT, see http://technet.microsoft.com/en-us/library/

cc739385.aspx.

Public and Private IPv4 Addresses

Every device on the Internet has its own unique public IPv4 address that is shared with no other device (a LAN also has at least one IPv4 address that is unique on the Internet) For

example, if you type a URL such as http://www.adatum.com into your Web browser, the

FQDN www.adatum.com identifies a Web server that has a public IPv4 address—for example,

207 46 197 32

Any organization that has an Internet presence is allocated one or more public IPv4 addresses that that organization and only that organization can use The Internet Assigned Numbers Authority (IANA) issues and controls public IPv4 addresses through various agencies—for example, the United Kingdom Education and Research Network (UKERNA)

In the case of a SOHO network, the ISP allocates one public IPv4 address from a range that IANA or one of its agencies has allocated to the ISP

Most organizations do not have enough public IPv4 addresses to allocate one to

every device on their networks Also, issuing public IPv4 addresses to computers in an organization’s network has security implications Instead, organizations use private IPv4 addresses for their internal networks and use NAT to translate these addresses to a public address or addresses for Internet access

Private IPv4 addresses should never be used on the Internet, and typically a router on the Internet ignores private IPv4 addresses An organization can use whatever private IPv4 address range it chooses without requiring permission from IANA Because private IPv4 addresses are internal to an organization, many organizations can use the same range of IPv4 addresses without causing IPv4 conflicts Most computers on internal networks do not need a unique public address but instead share a single public address that identifies their LAN and that NAT translates to their private addresses Only devices on a LAN that have

an Internet presence—for example, Web servers, e-mail servers, and DNS servers—require

a unique public address mapped through NAT to their internal private address

IANA has reserved the following three blocks of IPv4 address space for private networks:

n 10 0 0 0/8 (10 0 0 1 through 10 255 255 254)

n 172 16 0 0/12 (172 16 0 1 through 172 31 255 254)

n 192 168 0 0/16 (192 168 0 1 through 192 168 255 255)

In addition, the APIPA range 169 254 0 0/16 (169 254 0 1 through 169 254 255 254) is also

considered private because these addresses should never appear on the Internet However,

you should use this range only for automatic IPv4 address allocation through APIPA in an

isolated subnet You should not use this range in private networks that configure their devices

though DHCP or manual (static) configuration and use NAT to implement Internet access

Most organizations use only a small subsection of the private address space For example,

the 10 0 0 0/8 network contains more than 16 million host addresses, and very few organizations

need that many A commercial company with two private subnets might, for example, use

10 0 10 0/24 (10 0 10 1 through 10 0 10 254) and 10 0 20 0/24 (10 0 20 1 through 10 0 20 254) for

these subnets ICS uses the 192 168 0 0/24 address range (192 168 0 1 through 192 168 0 254),

and most WAPs also use this range of addresses

note prIVate NetWOrKS—the DeFINItIVe DOCUMeNt

The accurate definition of a private network is a network that uses RFC 1918 IPv4 address

space As you progress in your career as a network administrator, you will refer more and

more frequently to RFCs like RFC 1918 To view this RFC, see http://tools.ietf.org/html/rfc1918.

Connecting to a Network

If you are setting up a wired test or SOHO network from scratch, you likely start with a single

computer connected to your modem (either wired or wirelessly via a WAP), which in turn

provides a connection to the Internet Typically, most networks are connected to the Internet,

either directly or through other networks If your network is completely isolated, with no

connections to either the Internet or other LANs, then it is usually sufficient to let it configure

itself through APIPA

More commonly, you are adding a computer to an existing network (for example, a SOHO

network or a small test network) In this case, a DHCP service typically already exists on

the network, possibly on a computer configured to provide ICS, or (in the case of a wireless

network) from a WAP When you connect to the Internet, your ISP automatically configures

your dial-up or cable modem connection If you set up ICS, then the computer on your

network that directly accesses your modem automatically configures all the other computers

on its subnet

More Info INterNet CONNeCtION SharINg

For more information about ICS and an excellent illustrative diagram, see http://windowshelp

.microsoft.com/Windows/en-US/Help/bfd3bd31-82f0-4b9c-9cde-fb92bc2b14771033.mspx

This is a Windows Vista article, but it works for Windows 7 if you substitute “Change Adapter

Settings” for “Manage Network Settings.”

Typically, client computers on a network are set to receive their IP configurations

automatically However, if the computer you are adding is an ICS client, you need to access Network And Sharing Center, click Internet Options, click LAN Settings on the Connections tab, and clear the Automatically Select Connections check box in the Local Area Network (LAN) Settings dialog box You configure an ICS computer and an ICS client in a practice exercise later in this lesson

You can check if a computer is configured and get IPv4 configurations automatically by opening the Network And Sharing Center You do this by opening Control Panel, clicking Network And Internet, and then clicking Network And Sharing Center In the Network And Sharing Center, click Change Adapter Settings Right-click the local area connection that connects to your test network (typically, Local Area Connection) and choose Properties The Local Area Connection Properties dialog box appears, as shown in Figure 6-2 Note that the names of the antivirus supplier and the Ethernet controller manufacturer have been obscured for legal reasons

In this dialog box, you can select Internet Protocol Version 4 (TCP/IPv4) and click

Properties Unless you have chosen manual configuration by selecting Use The Following

IP Address, you should see that IPv4 is set up for automatic configuration, as shown in Figure 6-3 If you click the Alternate Configuration tab, you see that APIPA is used by default if DHCP information is not available

FIgUre 6-3 Automatic IPv4 configuration

Lesson 3 discusses the various configurations and combinations of wired and wireless

computers, modems, and WAPs you can use to set up a SOHO or a small test network Setting

up a production network is a much more complex procedure involving the use of multiple

firewalls, peripheral zones, NAT servers, and so on It is unlikely that the 70-680 examination

will ask you about setting up a fully secured production network in the enterprise In this

lesson, we connect the Canberra and Aberdeen computers on a private wired network and

(optionally) connect the Canberra computer wirelessly to a WAP that accesses the Internet

through a cable modem (or uses a composite device that is both a WAP and a cable modem)

and configuring ICS on that computer

To connect wirelessly to a WAP (if this is necessary), open the Network And Sharing Center

(shown in Figure 6-4) and click Connect To A Network You can select a network from the

list of those available You can also specify that the computer should always connect to this

network when it is in range

note UNCONFIgUreD WapS

Figure 6-4 shows the Canberra computer connected to an as-yet-unconfigured WAP

Unconfigured WAPs are typically called Default, have a password of admin, and allow

a client computer to connect to them This WAP is currently unconfigured because WAP

configuration is discussed in Lesson 3 Always configure your WAP; failure to do so is

a major security risk.

FIgUre 6-4 The Network And Sharing Center

Setting an IPv4 configuration

In the Internet Protocol Version 4 (TCP/IPv4) Properties dialog box shown in Figure 6-3, you can select Use The Following IP Address and type in a static IPv4 address, a subnet mask, and a default gateway You can also select Use The Following DNS Server Address and type

in the IPv4 address of a DNS server and an alternate DNS server the client can use if the first is unavailable Clicking Advanced lets you add more DNS servers You can also add the IPv4 addresses of one or more Windows Internet Naming Service (WINS) server if you need NetBIOS name resolution

However, many administrators prefer to use the Netsh command-line tool from an elevated command prompt For example, if you want to configure the Local Area Connection interface with an IPv4 address 10 0 0 11, a subnet mask 255 255 255 0, and a default gateway

10 0 0 11, you enter the following command:

netsh interface ipv4 set address "local area connection" static 10.0.0.11 255.255.255.0 10.0.0.11

If you also wanted to set the DNS server address as 10 0 0 11, you enter the following command:

netsh interface ipv4 set dnsservers "local area connection" static 10.0.0.11

If you wanted the interface to obtain its IPv4 configuration automatically (dynamically), you enter the following commands:

netsh interface ipv4 set address name="local area connection" source=dhcp

netsh interface ipv4 set dnsservers name="local area connection" source=dhcp

You use both the Internet Protocol Version 4 (TCP/IPv4) Properties dialog box and the

Netsh command to configure an interface in the practice later in this lesson

note NetSh SYNtaX

For backward compatibility, you can use netsh interface ip in place of netsh interface

ipv4 For IPv6 Netsh commands, you must specify IPv6 Note also for static settings, the

interface name is simply local area connection. The syntax name="local area connection”

is acceptable but not necessary. For dynamic configuration you need to use name="local

area connection”.

Troubleshooting Network Connectivity

As an IT professional, one of the most common problems you encounter is computers not

being able to connect to one another, to other internal networks within your organization, or

to the Internet In this section, you look at general troubleshooting tools that help you debug

network connectivity, as well as the Windows Network Diagnostics tool

Basic Troubleshooting

Connection problems can have many possible causes In wired networks, a cable could be

faulty or might not be connecting properly to its socket Interfaces that should get their

IP configurations dynamically could be set with a static configuration Where two or more

interfaces form a network bridge, one or more interfaces could have been removed from the

bridge In the enterprise environment, a DHCP or DNS server, or even a domain controller,

might have developed a fault (although there is typically a failover mechanism in this

situation) A firewall might be misconfigured

On a small network, ICS might be set up incorrectly or not set up at all A third-party WAP

could have been added to a wired network so that wireless computers can connect, but

the computer previously configured to provide ICS might not be reconfigured to obtain its

configuration from the WAP A WAP, network adapter, or modem could be faulty Your ISP

could be suffering an outage Newly installed software might have changed your connection

properties The list is practically endless

First principles always apply Start with the network and ensure that no cables have

been pulled out or are halfway out and causing unreliable connections Make sure all the

appropriate light-emitting diodes (LEDs) on the modem, WAP, and network interfaces are lit

when they should be lit and flickering when they should be flickering If a device shows no

sign of life, check that its power supply is connected to a power socket and to the device

Check out any illuminated red LEDs A red light does not always indicate a fault, but red

frequently signifies danger

If you are having problems with wireless connections, try switching the WAP off You

should then power down any computers that connect to the WAP through Ethernet cables

and possibly your wireless computers as well Wait a few minutes, switch the WAP back on,

and restart the computers If you suspect the modem, switch off the modem, the WAP, and all

network computers and then turn them on again in that order Check the WAP settings

Checking Computer to Computer Connectivity

Before you start to use the tools Windows 7 provides to check computer-to-computer connectivity, make sure the computer you are trying to connect to is switched on In a wired network, make sure it is plugged into the network If you are using ICS, make sure the ICS computer is switched on and running, otherwise none of the other computers will connect to the Internet If the computers on your network get their IPv4 configurations from a third-party WAP, make sure the WAP is switched on and connected to the modem

For a computer running Windows 7 to connect to other computers on a LAN, Network Discovery needs to be enabled on both the source and destination computers Network Discovery is enabled by default, but if you are having problems accessing other computers, check this setting by clicking Change Advanced Sharing Settings in the Network And Sharing Center Figure 6-5 shows the Advanced Sharing Settings dialog box

If a network connection is suffering intermittent problems, it is sometimes sufficient to disable and then enable the network connector device driver If this does not help, the device driver might be corrupt or out of date, or it might recently have been replaced by a new driver that is causing compatibility problems Chapter 4, “Managing Devices and Disks,” gives more details about updating, uninstalling, rolling back, and troubleshooting drivers

Troubleshooting IP Configuration

Command-line tools for troubleshooting IP configuration have been around for some time

and are well known The Ping tool is still widely used, although more firewalls block Internet

Control Message Protocol (ICMP) echo requests than used to be the case However, even