Dynamic
IP Mapping
The
advantage of dynamic tables that store IP mappings is that they are
updated automatically. To accomplish this, the dynamic tables
use two services: Domain Name System (DNS) and Windows Internet Name
Service (WINS). DNS and WINS perform the same functions as the Hosts
and Lmhosts files, but without the need for manual configuration.
Domain
Name System (DNS)
DNS
is a method for naming computers and network services. TCP/IP
networks use the DNS naming convention to locate computers and
services through user friendly domain names. When a user enters a
domain name in an application, the DNS service maps the name to an
IP address. The DNS naming system is organized in a hierarchical
fashion to allow scalability to large systems, such as the Internet.
By using a hierarchical system to create domain names, the computers
that store the domain name–to–IP address mapping records have
mappings for only their area. These computers, known as DNS servers,
only process queries for computers located in their respective
areas. As the mappings in the area change, Windows 2003-based DNS
servers are automatically updated with the new information.
Windows
Internet Name Service (WINS)
WINS
provides a distributed database for registering dynamic mappings of
NetBIOS names used on a network. WINS maps NetBIOS names to IP
addresses and allows NetBIOS names to be used across routers.
A
WINS server is not required for a pure Windows 2003 network but is
recommended for use in a mixed environment.
Name
Resolution in Windows 2003
Name
resolution is the procedure by which a name is resolved, or mapped,
to an IP address. When you enter a user-friendly name in an
application, the application determines whether the name is a host
or NetBIOS name. Current applications in Windows 2003 use the host
name resolution process, but some older applications, such as those
designed for Microsoft Windows NT, Windows 95, and Windows 98, still
use NetBIOS names. If the name resolution process fails, then the
application cannot communicate with the desired destination. If you
use an IP address, name resolution is not needed.
Host
Name Resolution Process
Host
names can be resolved directly by the Hosts file or by a DNS server.
The default name resolution procedure is as follows:
1.
Computer A enters a command, such as
FTP,
by using the host name of Computer B.
2.
Computer A checks to see if the specified name matches its local
host name.
3.
If not, then Computer A checks its Hosts file looking for Computer
B’s host name. If it finds the host name, it resolves it to an IP
address.
4.
If Computer A does not find Computer B’s host name in the Hosts
file, it sends a query to the DNS server. If the host name is found,
it is resolved to an IP address.
5.
If the host name is not found on the DNS server, Windows 2003 checks
for the name in the NetBIOS name cache. It does this because Windows
2003 treats the NetBIOS name as the host name.
6.
If the NetBIOS name cache does not have the host (NetBIOS) name, a
query is sent to the WINS server.
7.
If the WINS server cannot resolve the name, a broadcast message is
sent out on the network.
8.
If no host responds to the broadcast, the Lmhosts file is checked
for the host (NetBIOS) name.
