C# 4 and .NET 4

654 ❘ ChaPTer 24 netwOrkinG
UriBuilder, however, implements fewer properties, just enough to allow you to build up a complete URI.
These properties are read-write.
You can supply the components to build up a URI to the constructor:
UriBuilder MSPage = new
UriBuilder("http", "www.microsoft.com", 80, "SomeFolder/SomeFile.htm");
Or, you can build the components by assigning values to the properties:
UriBuilder MSPage = new UriBuilder();
MSPage.Scheme ="http";
MSPage.Host = "www.microsoft.com";
MSPage.Port = 80;
MSPage.Path = "SomeFolder/SomeFile.htm";
After you have completed initializing the UriBuilder, you can obtain the corresponding Uri object with
the Uri property:
Uri CompletedUri = MSPage.Uri;
iP addresses and dns names
On the Internet, you identify servers as well as clients by IP address or host name (also referred to as a
DNS name). Generally speaking, the host name is the human-friendly name that you type in a web browser
window, such as www.wrox.com or www.microsoft.com. An IP address is the identifier computers use to
identify each other. IP addresses are the identifiers used to ensure that web requests and responses reach the
appropriate machines. It is even possible for a computer to have more than one IP address.
Today, IP addresses are typically a 32-bit value. An example of a 32-bit IP address is 192.168.1.100. This
format of IP address is referred to as Internet Protocol version 4. Because there are now so many computers
and other devices vying for a spot on the Internet, a newer type of address was developed — Internet
Protocol version 6. IPv6 provides a 64-bit IP address. IPv6 can potentially provide a maximum number of
about 3 × 10 28 unique addresses. You will find that the .NET Framework allows your applications to work
with both IPv4 and IPv6.
For host names to work, you must first send a network request to translate the host name into an IP address,
a task carried out by one or more DNS servers.
A DNS server stores a table mapping host names to IP addresses for all the computers it knows about,
as well as the IP addresses of other DNS servers to look up the host names it does not know about. Your
local computer should always know about at least one DNS server. Network administrators configure this
information when a computer is set up.
Before sending out a request, your computer will first ask the DNS server to tell it the IP address
corresponding to the host name you have typed in. When it is armed with the correct IP address, the
computer can address the request and send it over the network. All this work normally happens behind
the scenes while the user is browsing the Web.
.neT Classes for iP addresses
The .NET Framework supplies a number of classes that are able to assist with the process of looking up IP
addresses and finding information about host computers.
IPAddress
IPAddress represents an IP address. The address itself is available as the GetAddressBytes property and
may be converted to a dotted decimal format with the ToString() method. IPAddress also implements
a static Parse() method, which effectively performs the reverse conversion of ToString() — converting
from a dotted decimal string to an IPAddress:
IPAddress ipAddress = IPAddress.Parse("234.56.78.9");
byte[] address = ipAddress.GetAddressBytes();
string ipString = ipAddress.ToString();
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