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Configure and Troubleshoot Network Protocols (part 1) - Configuring Internet Protocol Version 4

3/16/2011 10:31:17 PM
Network protocols comprise quite a substantial list. This section begins by looking at the protocols used when configuring a network adapter for local area network (LAN) connectivity. The Internet Protocol version 4 (IPv4) is still the dominant IP protocol in use on the Internet today. So this section begins by discussing IPv4 configuration and moves into configuring IPv6.

When you are configuring IP connectivity for a computer, you give consideration to the following items in no particular order:

  • What type of addresses (Public or Private) will be used?

  • Will a computer need a static or a dynamic IP address?

  • Is the network routed?

  • If so, are the default metrics for routing sufficient?

  • What name resolution services will be needed?

  • Is domain name system (DNS) registration needed?

  • Are NetBIOS-based applications still in use within the environment?

  • Is there a need for securing the communication protocols used by this computer?

The preceding list is not an exhaustive list of items to consider when configuring the Transmission Control Protocol/Internet Protocol (TCP/IP) settings on a computer. But this list is the focus for what is necessary to know for the 70-622 exam.

Configuring Internet Protocol Version 4

You can concern yourself with configuring the TCP/IP settings on a LAN in this section. 

IPv4 Address Primer

When configuring the TCP/IPv4 address settings on a computer, you must configure the IP address as well as the subnet mask. The IP address is a 32-bit binary address. The 32 bits are seen by the computer as a single stream of bits, as shown here:

11000000101010000000000000000001

For you to configure and utilize the 32 bits of 1s and 0s, they are separated into four octets using periods as separators. This now looks like the following assortment:

11000000.10101000.00000000.00000001

The four octets are then converted into their decimal equivalents. The decimal numbers are a conversion of the 32 bits of 1s and 0s. The preceding 32-bit address string looks like this when converted into decimal:

192.168.0.1

The subnet mask that must also be configured identifies the portion of the 32-bit address that represents the network and which portion represents the host on that network. Think of the mask as dividing the IPv4 address into a ZIP code (network) and a street address of a home within that ZIP code (host on that network).


When configuring network devices or hosts, as they are also called, you must consider some basic rules:

  • Every IP address configured for a host on a network must be unique.

  • The IP address consists of a network portion and a host portion.

  • Every IPv4 host requires an IP address.

  • Every IPv4 host requires a subnet mask.

  • Every IPv4 hosts requires a default gateway in a routed environment.

  • Every IPv4 host within a subnet should have the same subnet mask and default gateway to communicate with all hosts within the subnet and all subnets within the enterprise.

Alert

For local LAN communication, all that is required for successful communication is the IP address and subnet mask. If the network is routed or requires connectivity to the Internet, all IP hosts require an IP address, a subnet mask, and a default gateway address. Although there are ways around the requirement of a default gateway address, such as setting up static IP routes (which is a solution that is usually impractical except for the most extreme situations), assume every host in a routed environment requires a default gateway. Use this tidbit of information when concerned with minimum configuration settings for IP hosts. Note that if the Internet is part of the equation, DNS should also be required although it is sometimes overlooked.


IPv4 routable addresses that are available for consumption when configuring addresses on IP hosts consist of addresses within the following IPv4 ranges:

Class A: 1.0.0.0–126.255.255.255

Class B: 128.0.0.0–191.255.255.255

Class C: 192.0.0.0–223.255.255.255

Table 1 outlines in more detail the IPv4 address ranges and their descriptions.

Table 1. IPv4 Detailed Address Range and Descriptions
IPv4 Address RangeIPv4 Address Type
1.0.0.0–9.255.255.255 
11.0.0.0–126.255.255.255Class A Public IPv4 address ranges
10.0.0.0–10.255.255.255Class A Private IPv4 address range
127.0.0.0–127.255.255.254IPv4 Loopback range
128.0.0.0–169.253.255.255 
169.255.0.0–172.15.255.255 
172.17.0.0–191.255.255.255Class B Public IPv4 address ranges
169.254.0.0–169.254.255.255Automatic Private IP address (APIPA) range
172.16.0.0–172.31.255.255Class B Private IPv4 address range
192.0.0.0–192.167.255.255 
192.169.0.0–223.255.255.255Class C Public IPv4 address ranges
192.168.0.0–192.168.255.255Class C Private IPv4 address range
224.0.0.0–239.255.255.255Class D IPv4 Multicast range
240.0.0.0–255.255.255.255Class E IPv4 Experimental range (unused)

Notice there are portions taken out of each of the first three IPv4 class addresses for Private IP address use. The Private IP address ranges are used by an enterprise when there are not enough Public IP addresses allotted to the organization for internal consumption. A company may also make a strategic decision to use Private IP addresses internally to aid in disguising the addressing structure.

The use of Public versus Private IP addressing is more of a design discussion. You need to be concerned over which addressing is in use when you need to route packets over public networks and if you are going to need the use of Network Address Translation (NAT). An administrator of enterprise desktops is expected to be able to determine the different address types available for use and the issues surrounding their use.

You have two choices when configuring the TCP/IP IPv4 properties on a Windows Vista computer: Dynamic Host Configuration Protocol (DHCP) or manual assignment. Figure 1 displays the General tab of the IPv4 protocol when selected from the Networking tab.

Figure 1. The Internet Protocol version 4 (TCP/IPv4) Properties dialog box.


Tip

To access the dialog box displayed in Figure 1, follow these steps:

1.
Click Start > Control Panel > Network and Internet > Network and Sharing Center > Manage Network Connections.

2.
Select the appropriate network adapter.

3.
Right-click and select Properties.

4.
Select Properties on the General tab.

5.
Select the Internet Protocol Version 4 (TCP/IPv4) protocol and click Properties.

This is not a fast procedure, but other shortcuts are available through the GUI:

1.
Right-click the Network icon in the notification area.

2.
You are now in the Network and Sharing center, and you can follow the steps from this point in the preceding set of steps.


You can either manually enter the IP address or select for an IP address to be automatically obtained. For an automatic IP address to be obtained, your network requires a DHCP server to be configured and running. In a large enterprise, DHCP is used for IP configuration of most IP hosts within the enterprise. If you configure the Windows Vista client to automatically obtain its IP address, the computer becomes a DHCP client.

A consideration when using DHCP is where the DHCP server is located in relation to its DHCP clients. DHCP client requests are IP network broadcasts. Because an IP broadcast does not cross a router, routers form logical boundaries for a DHCP broadcast by a DHCP client. If a DHCP server is located on every network where there are DHCP clients, you have no issue. As your network size grows and additional subnets are configured, having a DHCP server per every LAN segment becomes impractical in most cases.

To get around this problem, Microsoft added another protocol to circumvent this issue. BOOTP relay, better known in Microsoft circles as DHCP relay, receives the DHCP broadcasts on a local LAN and forwards the request to a DHCP server. Through the use of DHCP relay, DHCP servers are able to exist in centrally managed locations remote from the clients. Figure 2 shows DHCP clients on three different LAN segments. Routers RTR-1 and RTR-2 require DHCP relay to be configured on both of their A interfaces to be able to forward DHCP broadcasts to the DHCP server located on the third LAN segment. Request For Comments (RFC) 1542 is a standards document written to clarify the functionality and purpose of BOOTP relay agents. BOOTP relay agents, or DHCP relay agents, allow the forwarding of DHCP discovery messages from one subnet to another subnet or directly to a specifically configured DHCP server. This is to allow DHCP clients located on subnets not directly serviced by a DHCP server to acquire a DHCP address from a remote DHCP server across a router.

Figure 2. Routers configured for DHCP relay.


If RTR-1 and RTR-2 are properly configured, the DHCP clients located off each of their A interfaces receive a DHCP address from the DHCP server if the DHCP server is also appropriately configured with three different DHCP scopes.

Note

Describing a DHCP scope and its configuration is beyond the scope (sorry to do that) of this book. Microsoft defines a DHCP scope to be an administrative grouping of IP addresses for computers on a subnet that use the DHCP service. The scope contains the following properties:

  • A range of IP addresses

  • A subnet mask

  • Lease duration values

  • DHCP scope options such as addresses for WINS servers, DNS servers, and router IP addresses

One issue regarding DHCP IP address availability is that a DHCP scope may run out of addresses if there are more clients requesting addresses than the scope is configured to offer.


APIPA

Microsoft clients also adhere to the Request For Comments (RFC) draft for IPv4 Link-Local addresses. The address range 169.254.x.y/16 has been set aside for this Internet Engineering Task Force (IETF) specification. Microsoft refers to this feature as Automatic Private IP Addressing (APIPA). APIPA works like this: If a Microsoft Windows computer is configured as a DHCP client and the computer fails to receive an IP address, the computer self-configures an address in the 169.254.x.y/16 range. The computer’s IP protocol stack uses the Address Resolution Protocol to determine if the address it has chosen within the APIPA range is already in use on the local network.

Note

For more information on Microsoft’s implementation of APIPA addressing, review this support article at http://support.microsoft.com/kb/931550.


Microsoft clients have slowly decreased the wait interval that is used before using an APIPA address. Windows Vista clients now wait a period of six seconds according to Microsoft’s support article 931550. This six-second wait period before using an APIPA address applies to all 32-bit and 64-bit editions of Windows Vista.

Note

A type of shorthand notation has been adopted for referencing IP addresses. In the preceding pages, you saw references like this to an IP address:

169.254.x.y/16

The /16 value notates the number of contiguous high-order 1 bits in the 32-bit subnet mask. The notation value /16 represents in decimal notation the subnet mask of 255.255.0.0. This type of notation is referred to as prefix length. A classless network specification known as Classless Internet Domain Routing (CIDR) introduced this notation. This specification is discussed later.

The variables x and y used in this address denote any valid values that can be used here. In this case, any values between 0 and 255 could be placed in each of the locations as long as they adhere to the rules of the IPv4 Link-Local Addresses draft or Microsoft’s implementation of APIPA.


In addition to an IP address and a subnet mask, as you previously learned, in a routed environment an IP default gateway address must also be configured. Once again, if a DHCP server is being used to provide automatic addressing of the IP hosts, the DHCP server’s scope is configured with an appropriate IP default gateway to be handed out to the clients as well. Back to the APIPA discussion, if a Microsoft Vista client fails to get a DHCP assigned address and an APIPA address is used, no IP default gateway is configured. Therefore, the clients that utilize this self-configuring mechanism are restricted to the LAN itself for all its communication until it reaches a DHCP server or is otherwise manually assigned another IP address, subnet mask, and default gateway address. Microsoft’s APIPA implementation specifies for a five-minute interval between polling attempts for a DHCP server by a DHCP client.

DNS

The final piece of IP configuration data left to configure is the domain name system (DNS) server addresses. The DHCP service can provide the two DNS server addresses. Two DNS server addresses should be configured for fault tolerance. Figure 1 shows the dialog box that refers to them as the Preferred DNS server and the Alternate DNS server. If any valid response is received from the Preferred DNS server address, the second, or Alternate, DNS server address is unused for now. A DNS client fails over to the Alternate DNS server address that is configured whenever the Preferred DNS server fails to respond to a query.

DNS name resolution is used to resolve fully qualified domain names (FQDNs) to an IP address. A fully qualified domain name appears like the following:

pablo.nittci.com

In this case, pablo is the name of host device and nittci.com is the domain name component that is appended to the hostnames.

Note

The trailing period is used in the preceding example because an FQDN represents absoluteness; there is no trailing suffix that is or can be appended. An FQDN for a device or host represents that host absolutely in the DNS tree hierarchy. With that in mind, the trailing period is often unused when FQDNs are discussed. Just remember that it is a part of the formal definition of an FQDN. It is noteworthy, but it is not test worthy.

You can find a more complete discussion on the DNS naming hierarchy in the Windows Server 2003 TechCenter. The following URL discusses the DNS domain name space:

http://technet2.microsoft.com/windowsserver/en/library/133621fb-2d7c-4b4e-ba6f-f0e275a74fa41033.mspx?mfr=true


The order that DNS servers are configured in either the DHCP scope or in the dialog box shown in Figure 1 is significant. Because the Primary DNS server is used until there is no response from it, it obviously receives all the requests during its operation from the clients that are configured to use it first. Therefore, the golden rule is to always configure clients with the DNS server that is closest in proximity in regard to network hops and WAN links as their Primary DNS server. This keeps network traffic low on the LAN or WAN links and should aid in making the DNS responses more expedient.

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