Every computer on a Windows Network has a Computer Name (under Control Panel: Networks: Identification: Computer Name). This Computer Name is the same as the NetBIOS Name (Network Basic Input Output System) and may be up to 15 bytes long. A NetBIOS Name is part of Windows OSI Application Layer interface for network protocols.
Each computer on a TCP/IP network is assigned an IP address. This can be done one of two ways:
- Manually. The IP address is manually entered at each computer. Along with the IP address, a Subnet Mask and a Default Gateway are also usually entered. The Subnet Mask is used over the given IP address to determine which sub-network the IP address is part of. (See my article on TCP/IP.) The Default Gateway is where packets go when they have to leave the network.
- Automatically. The IP address is automatically assigned to the computer when the computer logs in by contacting a DHCP Server/Router (Dynamic Host Configuration Protocol) or PPP Dial-Up Router (Point-to-Point Protocol). DHCP Server/Router is used when the computer is connecting to a local LAN. The PPP Dial-up Router is used when the user is connecting to a remote LAN or ISP.
However, an IP address is insufficient. On any network, a computer is ultimately identified by its MAC address. In addition, different systems will use different user-friendly names equivalent to the IP address. Here are four ways of resolving IP addresses at boot up:
- WINS. Windows Internet Name Service resolves IP addresses to NetBIOS Names which are tied to the MAC address.
- DNS. Domain Name Service resolves IP addresses to FQDNs (Fully Qualified Domain Names). A FQDN has two parts: the hostname and the domainname. The hostname is the same as the NetBIOS Name in Windows networks. The domainname follows the Domain Name System convention, which is a hierarchical naming convention for domains. EG: The hostname/NetBIOS Name of "fred" may be joined with the domainname "dogs.com" to form the FQDN of "fred.dogs.com" which may have an IP address of "220.127.116.11". Two points to watch out for:
- DNS can stand for either Domain Name Service or Domain Name System, which are related but not equivalent!
- "Host" can refer to the computer itself, the NetBIOS name, or the FQDN!
- LMHOSTS. A file which functions like WINS in that the NOS uses it to resolve IP address with NetBIOS Names. It must be manually created and placed in
\WINDOWS\ETCfor Windows 95 or
\WINNT\SYSTEM32\DRIVERS\ETCfor Window NT. It is basically a two column file with IPs in the first column and NetBIOS Names in the second. LMHOSTS is also sometimes called LMHOSTS.SAM.
- HOSTS. A file which functions like DNS in that the NOS uses it to resolve IP address with FQDNs. It must be manually created and placed in
\WINDOWSfor Windows 95 or
\WINNT\SYSTEM32\DRIVERS\ETCfor Window NT. It is basically a two column file with IPs in the first column and FQDNs in the second. HOSTS is also sometimes called HOSTS.SAM, HOST, or HOST.SAM.
When an IP address is resolved to a MAC address it is stored in a ARP cache (Address Resolution Protocol). If a system has IP addresses but they are not tied to MAC addresses, then an ARP broadcast is sent out to ask each piece of hardware if it is that IP address. If it is then the resolved IP and MAC address are stored in the ARP cache.