Configuring and Troubleshooting TCPIP Addressing

Configuring and Troubleshooting TCP/IP Addressing

An IP address is a series of numbers that represents a computer (for example, 131.108.116.55). Each of the numbers in an IP address is an octet, which is made up of 8 bits; the whole IP address is 32 bits. IP addresses are typically displayed in a decimal format called dotted-decimal notation. Each host that requires connectivity on a TCP/IP network requires its own unique IP address.

If you were to look at 131.108.116.55 in binary, as the computer sees it, you would see 10000011 01101100 01110100 00110111. The easiest way to convert dotted-decimal notation to binary is to learn the mechanics of the binary system. By knowing that the smallest value that an IP address octet can take is 0 and the largest value that an IP address octet can take is 255, you can make a chart such as the one shown in Table 1.

Table 1. Decimal-to-Binary Conversion Basics

	128(27)	64(26)	32(25)	16(24)	8(23)	4(22)	2(21)	1(20)
255	1	1	1	1	1	1	1	1
0	0	0	0	0	0	0	0	0

Table 1 represents the 8 binary digits that make up a single IP address octet. If you have a value of decimal 255, its binary equivalent is 11111111, and if you have a value of decimal 0, its binary equivalent is 00000000.

IP addresses are organized by class. There are three basic classes: Class A, Class B, and Class C. Table 2 defines the range and number of hosts included with each class of addresses.

Table 2. IP Address Classes

Class	Address Range	Number of Network IDs	Number of Host IDs
A	1-126	126	16,777,214
B	128-191	16,384	65,534
C	192-223	2,097,152	254

A subnet mask effectively breaks an IP address into two parts: the network identifier and the host identifier.

When the subnet bits match, the host and destination host are on the same subnet, and no routing is needed. When the subnet bits don't match, the destination host is on a remote network, and the packets are sent to the router.

The Internet community has standardized default subnet masks for each of the three IP address classes. The subnet masks for these address classes are defined in Table 3.

Table 3. Default IP Class Subnet Masks

Address Class	Bits for Subnet Mask	Subnet Mask
A	11111111 00000000 00000000 00000000	255.0.0.0
B	11111111 11111111 00000000 00000000	255.255.0.0
C	11111111 11111111 11111111 00000000	255.255.255.0

If a computer has an IP address of 142.146.102.45 and a subnet mask of 255.255.0.0, the first two octets (142.146) identify the network, and the last two octets (102.45) identify a specific host on that network.

Using Variable Length Subnet Masks, also known as subnet addressing, allows you to borrow bits from the host ID portion of an IP address and apply them to the network ID.

Suppose that you have been assigned a Class B address of 172.18.0.0. Further suppose that you now need to create four separate networks from your one IP address range. To do so, you borrow 3 bits from the host ID field. These 3 bits let you configure six separate subnets.

A default gateway is the IP address of the router that the packets from a host should use to leave the subnet. The typical process of how a packet leaves a host and gets to a destination is as follows:

1. Computer A looks up the IP address of Computer E by using a query to a DNS server.

2. Computer A determines whether the IP address of Computer E is local or remote by comparing its own IP address to that of Computer E.

3. If the address is remote, Computer A sends the packets to the default gateway's MAC address. The MAC address of the default gateway is determined via an ARP broadcast.

4. The default gateway forwards the packets on to the next router, according to its routing table.

5. If Computer E's IP address is on the same subnet as Computer A, the IP address of Computer E is resolved to the MAC address through an ARP broadcast.

6. Computer A and Computer E then communicate with one another, and there is no need for routing.

Several changes and improvements have been made to TCP/IP in Windows Server 2003:

• netsh can be used to reset TCP/IP.

• netstat can display PIDs.

• Internet Group Management Protocol version 3 (IGMPv3) is supported.

• Interface speed route metric determination is possible.

• IPv6 is supported.

After you've performed the initial configuration of TCP/IP, you still might need to configure some additional settings on the protocol. If you click the Advanced button in the TCP/IP Properties dialog box, the Advanced TCP/IP Settings dialog box appears, and you can change settings on the following tabs:

• IP Settings This tab displays the currently configured IP address and default gateway.

• DNS This tab allows you to configure additional multiple DNS servers that the network connection should use and the order in which they should be contacted.

• WINS The WINS tab allows you to configure the WINS servers that are to be used to resolve NetBIOS hostnames to IP addresses on the network.

• Options The Options tab contains only one item in Windows Server 2003: TCP/IP Filtering. With this option, you can control the type of TCP/IP information that is sent to a computer.

Table 4 provides a list of common TCP port numbers. Table 5 presents some common UDP port numbers. Table 6 covers common Internet protocol numbers.

Table 4. Common TCP Port Numbers

TCP Port Number	Description
20	FTP data channel
21	FTP control channel
22	SSH Remote Login Protocol
23	Telnet
25	SMTP
53	DNS
69	TFTP
79	Finger
80	HTTP
109	POP2
110	POP3
137	NBNS
138	NetBIOS Datagram Service
139	NetBIOS Session Service
161	SNMP
443	HTTPS

Table 5. Common UDP Port Numbers

TCP Port Number	Description
20	FTP data channel
21	FTP control channel
22	SSH remote login protocol
23	Telnet
25	SMTP
53	DNS
69	TFTP
79	Finger
80	HTTP
109	POP2
110	POP 3
137	NBNS
138	NetBIOS datagram service
139	NetBIOS session service
161	SNMP
520	RIP

Table 6. Common Internet Protocol Numbers

Protocol Number	Protocol
1	ICMP
2	IGMP
3	GGP
4	IP in IP (encapsulation)
5	ST
6	TCP
7	CBT
8	EGP

Automatic Private IP Addressing (APIPA) allows a DHCP-configured computer to automatically assume an IP address from the range 169.254.0.1 through 169.254.255.254, with a subnet mask of 255.255.0.0, when a DHCP server cannot be contacted. Although APIPA does provide a client with an IP address if a DHCP server cannot be contacted, the only guarantee that is made is that the IP address the client uses will not belong to any other computer on its IP subnet.

APIPA does not provide any information to the computer beyond the IP address and subnet mask. This means that a computer possessing an APIPA IP address will not be able to communicate with other computers that are working with correctly assigned IP addresses and subnet masks. In addition, APIPA receives no default gateway and thus is unable to communicate outside its IP subnet.

There are several tools for troubleshooting TCP/IP problems, including the following:

• ping The ping command is used to test basic network connectivity between two computers. This testing is done over local and remote networks.

• ipconfig The ipconfig command can be used to quickly determine what settings have been configured for the network adapters in computers.

• Network Diagnostics The Network Diagnostics tool is available in Windows XP and Windows Server 2003, and you can use it to perform many of the same tests that were reviewed in Chapter 1, "Configuring and Troubleshooting TCP/IP Addressing," plus many more, all from within the Windows Graphical User Interface (GUI).

• netsh The netsh command is an advanced configuration and troubleshooting command that helps you to manage almost any networking-related component on your Windows Server 2003 computer; note, however, that it does require you to have knowledge of the result you're trying to achieve. The netsh command can be used interactively or via scripting to manage networking-related configurations such as those for the Windows Firewall, DHCP, WINS, TCP/IP configuration and IP Security (IPSec) settings, as well as many other tasks.