TCP/IP Configuration Facts

The following table summarizes many of the configuration settings for a TCP/IP network.

Parameter		Purpose
IP address		Identifies both the logical host and logical network addresses. Two devices on the same network must have IP addresses with the same network portion of the address.
Subnet mask		Identifies which portion of the IP address is the network address. Two devices on the same network must be configured with the same subnet mask.
Default gateway		Identifies the router to which packets for remote networks are sent. The default gateway address is the IP address of the router interface on the same subnet as the local host. Without a default gateway set, most clients will be unable to communicate with hosts outside of the local subnet.
Host name		Identifies the logical name of the local system.
DNS server		Identifies the DNS server that is used to resolve host names to IP addresses.
MAC address		Identifies the physical address. On an Ethernet network, this address is burned in to the network adapter hardware.

Note: A host requires an IP address and subnet mask to communicate on a single subnet. A default gateway address is required to enable inter-subnet communications. At least one DNS server address is required for the host to use hostnames when contacting other hosts.

Several of the TCP/IP configuration settings can be assigned through the following methods:

Method	Description
Dynamic Host Configuration Protocol (DHCP)	A DHCP server is a special server configured to pass out IP address and other IP configuration information to network clients. The DHCP server is configured with a range of IP addresses it can assign to hosts. The DHCP server can also be configured to pass out other IP configuration such as the default gateway and DNS server addresses. The DHCP server ensures that each client has a unique IP address. DHCP is a TCP/IP protocol. Any client configured to use DHCP can get an IP address from any server configured for DHCP, regardless of the operating system. DHCP requires a DHCP server and minimal configuration.
Automatic Private IP Addressing (APIPA)	APIPA is a Microsoft implementation of automatic IP address assignment without a DHCP server. Using APIPA, hosts assign themselves an IP address on the 169.254.0.0 network (mask of 255.255.0.0). With APIPA: The host is configured to obtain IP information from a DHCP server (this is the default configuration). If a DHCP server can't be contacted, the host uses APIPA to assign itself an IP address. The host only configures the IP address and mask. It does not assign itself the default gateway and DNS server addresses. For this reason, APIPA can only be used on a single subnet. Use APIPA as a fail safe for when a DHCP server is unavailable to provide limited communication capabilities.
Static (manual) assignment	Using static addressing, IP configuration information must be manually configured on each host. Use static addressing: On networks with a very small number of hosts. On networks that do not change often or that will not grow. To permanently assign IP addresses to hosts that must always have the same address (such as printers, servers, or routers). For hosts that cannot accept an IP address from DHCP. To reduce DHCP-related traffic. Note: Static addressing is very susceptible to configuration errors and duplicate IP address configuration errors (two hosts that have been assigned the same IP address). Static addressing also disables both APIPA and DHCP capabilities on the host.

Special Address Facts

Special Address Facts

You should understand the following special addresses:

IP Address and Class Facts

IP addresses allow hosts to participate on IP based networks. An IP address:

• Is a 32-bit binary number represented as four octets (four 8-bit values). Each octet is separated by a period.
• IP addresses can be represented in one of two ways:
  • Decimal (for example 131.107.2.200). In decimal notation, each octet must be between 0 and 255.
  • Binary (for example 10000011.01101011.00000010.11001000). In binary notation, each octet is an 8-digit number.
• The IP address includes both the network and the host address.
• Each IP address has an implied address class that can be used to infer the network portion of the address.
• The subnet mask is a 32-bit number that is associated with each IP address that identifies the network portion of the address. In binary form, the subnet mask is always a series of 1's followed by a series of 0's (1's and 0's are never mixed in sequence in the mask). A simple mask might be 255.255.255.0. read more...