[This is preliminary documentation and subject to change]

# About Name Resolution

In order for people to reach your site on an intranet or the Internet, you must have a unique IP address that identifies your computer on the network. This address takes the form of a long string of numbers separated by dots (for example, 172.16.255.255). Because a numeric address is difficult for people to remember, text names or "friendly names" are used to provide visitors with an easy-to-remember address, such as www.microsoft.com. Name resolution involves supplying the correct numerical address from the friendly name that was typed into a client browser. This section describes different name resolution systems.

- Intranet Name Resolution Systems
- Internet Name Resolution
- Hosting Multiple Sites by Assigning Ports, Addresses, and Host Header Names

For additional information, see the Windows documentation, accessible by clicking Help on the Start menu.

## Intranet Name Resolution Systems

An intranet is a private local area network (LAN) that uses Internet technology. To receive and deliver information packets successfully, each computer's IP address must be successfully mapped to its text name. The names and addresses can be assigned by using any of several different name-to-address resolution systems. You should make your choice based on the size of your intranet, how often computers are added or moved, and the software installed on Microsoft®

Windows Whistler Server. The following sections describe how computers on intranets receive their names and addresses.

### IP Address Assignment

IP addresses can be assigned in two ways: static or dynamic. Your network can use either static IP addresses, dynamic IP addresses, or a mixture of both.

- Static The system administrator assigns and tracks IP addresses for each computer on the intranet. Static assignment works best on small, infrequently changing networks , or when you want to run multiple sites (each responding to a different IP address) on one installation of IIS.
- Dynamic A Dynamic Host Configuration Protocol (DHCP) server temporarily leases an IP address to a client when the client logs on to the network. When a client logs on, the DHCP server assigns an IP address from its pool of currently available addresses. As the end of the lease approaches, the client computer negotiates with the server to renew the lease if necessary. When the client logs off, the address is released again and can be reassigned to a new client. A DHCP server relieves the system administrator of the burden of tracking IP address assignment and is particularly useful on large or frequently changing networks. A DHCP server permits only one IP address to be assigned to each computer on the network.

Note If you want to assign multiple IP addresses to one network card, then you must use a static address assignment for that computer.

### Name Resolution Systems

Windows networking components rely on the NetBIOS naming convention. In contrast, TCP/IP components rely on a naming convention known as the Domain Name System (DNS). Under Windows, the DNS host name defaults to the same name as the NetBIOS computer name. The mapping of computer names to IP addresses can be done in two ways:

- Static The system administrator creates a text file, called a HOSTS file (for DNS names), or an LMHOSTS file (for NetBIOS names), and enters each computer's name and IP address. The file is then distributed on the network. When a request for a connection to another computer is made, the file is used to resolve the name to the correct IP address. This system works well for simple networks that change infrequently.
- Dynamic When a client computer logs on, a DHCP server assigns an address and sends the IP address assignment to a Windows Internet Name Service (WINS) server. The WINS server registers the computer's name, and when a request is made for a NetBIOS computer name, the WINS server resolves the name to the correct IP address. This automatic recognition and mapping of computer names and addresses eases the administrative burden of large or frequently changing networks.

DNS names are typically resolved using static information. The DNS server contains a portion of the static database listing host names and addresses. If the requested name is not in the DNS server's portion of the database, it sends a query to other DNS servers to get the requested information. The DNS server that runs on Windows can be configured to query a WINS server for name resolution of the lower levels of the DNS hierarchical naming structure. Because WINS assigns computer names dynamically, this effectively changes DNS from a static system to a dynamic system.

If you are setting up multiple Web or FTP sites on a single server, and each site has its own IP address, you may encounter problems with automatic DNS registration. To ensure correct IP binding and DNS registration, disable Windows Whistler Server automatic DNS registration and manually configure DNS registration for the sites. For more information about disabling automatic DNS registration and manually configuring DNS registration, see the Windows Whistler Server documentation.

If you want to assign multiple names to one computer, you must use a static name assignment for the computer. On one computer you can map multiple names to one IP address; or you can use multiple names, each one mapped to its own IP address. For more conceptual information about naming sites, see Hosting Multiple Sites by Assigning Ports, Addresses, and Host Header Names later in this section. For procedural help, see Naming Web Sites.

## Internet Name Resolution

On the Internet, the Domain Name System (DNS) is used to resolve text ("friendly") names to IP addresses for sites. This section describes how name resolution works.

The DNS names are recorded by InterNIC, an organization that manages name and address assignment on the Internet. InterNIC operates a distributed database that contains all the registered domain names. When a client computer requests a connection to a site using a domain name, the request is transmitted to a series of computers called the Domain Name Servers.

The Domain Name Servers are located in thousands of organizations around the world. The Domain Name Servers return the IP address that corresponds to the requested domain name, and then the client request is routed to the appropriate site. Getting an Internet Name and Address contains information about registering a domain name for your site.

## Hosting Multiple Sites by Assigning Ports, Addresses, and Host Header Names

This section explains how to assign identification information to Web sites. Each Web site has a unique, three-part identity it uses to receive and to respond to requests:

- A port number
- An IP address
- A host header name

By changing one of these three identifiers, you can host multiple sites on a single computer.

### Port Numbers

By using appended port numbers, your site would only need one IP address to host many sites. In order for clients to reach your site, they would need to append a port number at the end of the static IP address (except for the default Web site, which uses port 80). The following graphic depicts a computer using port numbers to host multiple Web sites.

Using this method of hosting multiple sites requires clients to type in the actual numerical IP address followed by a port number. Host names or "friendly names" cannot be used.

### Multiple IP Addresses

To use multiple IP addresses, you must add the host name and its corresponding IP address to your name resolution system (typically DNS). Then clients need only type the text name in a browser to reach your Web site. If you use multiple IP addresses, you will need an additional network card for each IP address. The following graphic depicts a computer using multiple IP addresses to host multiple Web sites.

Note If you are using this method to host multiple sites on the Internet, you also need to register the text names with InterNIC.

### Host Header Names

Finally, you can also use host header names with a single static IP address to host multiple sites. Like the previous method, you still add the host name to your name resolution system (typically DNS). The difference is that once a request reaches the computer, IIS uses the host name passed in the HTTP header to determine which site clients are requesting. The following graphic depicts a computer using host header names to host multiple Web sites.

If you are using this method to host multiple sites on the Internet, you also need to register the friendly names with InterNIC.

Note You cannot use host headers when using Secure Sockets Layer (SSL) because HTTP requests using SSL are encrypted. Host headers are part of the encrypted request and cannot be interpreted and routed to the correct site.

Be aware that older browsers are unable to pass host header names back to IIS. Microsoft® Internet Explorer 3.0, Netscape Navigator 2.0, and later versions of both browsers support the use of host header names; earlier versions of the two browsers do not.

Visitors using older browsers reach the default Web site for the IP address and need additional support to reach the correct site. For instructions to enable host header support for older browsers, see Supporting Host Header Names in Older Browsers. For instructions on how to assign names, see Naming Web Sites. To find out how to add additional sites to your IIS installation, see Adding Sites.

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