TCP/IP Part III

Host Names

A host name is an alias assigned to a computer administrator to identify a TCP/IP host. The host name does not have to match the NetBIOS computer name, and can be any 256-character string. Multiple host names can be assigned to the same host.

A host name always corresponds to an IP address that is stored in a HOSTS file or in a database on a DNS or NetBIOS name server. Windows NT also uses the LMHOSTS file to map host names to IP addresses.

Host Name Resolution

HNR is the process of mapping a host name to an IP address. Before the IP address can be resolved to a hardware address, the host name must be resolved to an IP address.

HOSTS file

A local text file in the same format as the 4.3 Berkeley Software Distrubution (BSD) UNIX\Etc\Hosts file. This file maps host names to IP addresses. This file is typically used to resolve host names for TCP/IP utilities. C:\%system root%\system32\drives\etc

Ex. 127.0.0.1 localhost loopback

LMHOSTS file

A local text file that maps IP addresses to the NetBIOS computer names of Windows networking computers on remote networks. C:\%system root%\system32\drives\etc

Ex. 130.20.7.80 #PRE #DOM:

Domain Name System (DNS) server

A server that maintains a database of IP address/computer name (host name) mappings.

NetBIOS Name Server (NBNS)

A server implemented under RFCs 1001 and 1002 to provide name resolution of NetBIOS computer names resolution of NetBIOS computer names. The Microsoft implementation of this is WINS

Local broadcast

A broadcast on the LAN for the IP address of the destination NetBIOS name.

Domain Name System (DNS)

The Domain Name System (DNS) is similar to a telephone book. In DNS, the host computer contacts the name of a computer and a domain name server cross references the name to an IP address. The Domain Name System works using three main components: resolvers, name servers, and the domain name space.

With basic DNS communication, a DNS client, or resolver, sends queries to a name server. The server returns the requested information, or a pointer to another name server, or a failure message if the request can not be satisfied.

The purpose of the DNS database is to translate computer names into IP addresses.

Resolvers - The function of the resolvers is to pass name requests between applications and name servers. The name request contains a query. For example, the query might ask for the IP address of a Web site. The resolver is often built into the application or is running on the host computer as a library routine.

Name Servers - Name servers take name requests from resolvers and resolve computer (or domain) names to IP addresses. If the name server is not able to resolve the request, it may forward the request to name server that can resolve it. The name servers are grouped into different levels that are called domain.