Finding IP Address Information

One of the biggest challenges of network programming is dealing with network configurations of individual workstations and servers. When sending data across the network, you often need to determine the IP network information for the system running your program. The Windows OS family offers many ways to determine IP configuration information, both manually and from within a program. This section demonstrates a few of the ways that you can use to determine IP configuration information both manually and within your C# programs.

Using ipconfig

The ipconfig program displays IP network information for each active network interface on the system. The default form of ipconfig displays basic information for each network device:

C:\>ipconfig
Windows NT IP Configuration
Ethernet adapter El90x1:
    IP Address. . . . . . . . . : 192.168.1.6
    Subnet Mask . . . . . . . . : 255.255.255.0
    Default Gateway . . . . . . : 192.168.1.1
PPP adapter NdisWan5:
    IP Address. . . . . . . . . : 0.0.0.0
    Subnet Mask . . . . . . . . : 0.0.0.0
    Default Gateway . . . . . . :
C:\>

Here, the ipconfig program found two network interfaces configured on the workstation. The first interface is an Ethernet card configured for a LAN with a static IP address assigned to the workstation. The second device is a PPP connection configured to use a modem in the workstation. Because the PPP connection obtains its IP information dynamically when the PPP session starts, the values set by default in the workstation are zeroed. When the PPP connection is enabled, the assigned IP information is displayed.

To obtain more detailed information about a device, use the /all switch for the ipconfig command, as shown here:

C:\>ipconfig /all
Windows NT IP Configuration
    Host Name . . . . . . . . . : shadrach.blum.lan
    DNS Servers . . . . . . . . : 192.168.1.1
                   192.168.1.2
                   192.168.1.3
    Node Type . . . . . . . . . : Broadcast
    NetBIOS Scope ID. . . . . . :
    IP Routing Enabled. . . . . : No
    WINS Proxy Enabled. . . . . : No
    NetBIOS Resolution Uses DNS : No
Ethernet adapter El90x1:
    Description . . . . . . . . : 3Com EtherLink PCI
    Physical Address. . . . . . : 00-50-DA-10-78-67
    DHCP Enabled. . . . . . . . : No
    IP Address. . . . . . . . . : 192.168.1.6
    Subnet Mask . . . . . . . . : 255.255.255.0
    Default Gateway . . . . . . : 192.168.1.1
PPP adapter NdisWan5:
Description . . . . . . . . : NdisWan Adapter
    Physical Address. . . . . . : 00-00-00-00-00-00
    DHCP Enabled. . . . . . . . : No
    IP Address. . . . . . . . . : 0.0.0.0
    Subnet Mask . . . . . . . . : 0.0.0.0
    Default Gateway . . . . . . :
C:\>