Windows
There are three ways to examine, verify, and configure wire interface information in Windows 11: the Settings app, the Control Panel, and the command line.
The Settings App
To find and verify the network configuration in Windows 11 using the graphical user interface (GUI), open the Settings app and the Network & Internet section. A host may have several interfaces; you must select an individual interface to find its addresses and other information. Figure 4-1 illustrates the Network & internet section for a wired (Ethernet) interface.
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FIGURE 4-1 Network Section of the Windows 11 Settings App
Several lines are of interest here:
IP assignment: Indicates whether the host’s address was assigned manually or through DHCP.
DNS server assignment: Indicates whether the host’s DNS server address was assigned manually or through DHCP.
Link speed: Indicates the speed of the physical connection. Chapter 9, “Bandwidth, Delay, and Jitter,” will consider bandwidth in more detail.
Link-local IPv6 address: Computed as described in Chapter 3, “Routing and Switching.”
IPv4 address: Indicates the IPv4 address assigned to the Ethernet interface.
IPv4 DNS servers: DNS servers used to translate (resolve) domain names to IPv4 addresses.
Physical address (MAC): Indicates the physical address assigned to the interface by the manufacturer.
There are several lines with an Edit button to their right. Clicking the button to the right of IP assignment will allow you to manually assign an IP address rather than depending on a DHCP server. Once you have selected manual, rather than DHCP, assignment, you can change the IPv4 address field.
The Control Panel
A second place you can see the physical and interface addresses on Windows 11 is through the Control Panel. Once you have opened the Control Panel, select Network & Internet, then View Network Status and Tasks. Following this process opens a screen with the label View your basic network information and set up connections at the top.
Once there, select the Ethernet port to see the wired interface information.
Selecting the interface will cause a dialog to appear with some basic information, as shown in Figure 4-2.
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FIGURE 4-2 Windows 11 Interface Status Dialog
This dialog shows some basic information about the interface, including
IPv4 Connectivity, IPv6 Connectivity: Whether this host has Internet connectivity via IPv4 or IPv6
Media State: Whether the interface is enabled or disabled
Duration: How long this interface has been active and connected
Speed: The speed of the connection
Bytes Sent: The number of octets of data this host has transmitted on this interface
Bytes Received: The number of octets of data this host has received on this interface
The Disable option does precisely what it sounds like: disables this interface.
The Diagnose option runs the Windows Network Troubleshooter. The troubleshooter checks the interface’s status and whether the interface has a connection and then tries to ping various addresses. If the interface does not appear connected, the troubleshooter will attempt to reset the interface, release and renew any addresses assigned through DHCP, and take other actions.
The Properties option brings up another dialog, shown in Figure 4-3.
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FIGURE 4-3 Control Panel Interface and Properties Dialogs in Windows 11
Figure 4-3 shows two different dialogs. On the left is the Properties dialog for the wired information. Clicking some items in the list will only enable the Install and Uninstall options, while others will also enable the Properties option.
If you select Internet Protocol Version 4, the dialog on the figure’s right will pop up. This dialog allows you to configure how the interface obtains an IPv4 address and DNS server information—automatically or manually. You can configure an IPv4 address in the provided space if the manual option is selected.
Returning to the Ethernet Status dialog, selecting the Details option will cause a dialog to pop up containing the current interface physical address, interface address, DHCP lease information, DHCP server, and DNS server. This dialog will also display the subnet mask on some versions of Windows.
The Command Line
A command-line interface (CLI) is interactive: the user types commands and the host returns some response, usually text. Network engineers tend to work with CLIs more than GUIs because
CLIs tend to respond more quickly.
CLIs require fewer resources, so they can be implemented in a broader range of devices.
Text output typically contains a higher density of textual information than GUIs.
CLIs are more amenable to automation.
Powershell is the best tool on a Windows 11 host to access a command line. Most Windows hosts have Powershell installed, but it is available in the Microsoft Store if not. To display the physical interface from Powershell, use the command getmac /v from the CLI prompt, as shown in Figure 4-4.
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FIGURE 4-4 Displaying the Physical Interface Address from Powershell
Each interface has a single line of output with the following:
Connection Name: Matches the interface name in GUI
Network Adapter: Identifies the Interface manufacturer
Physical Address: Indicates whether the interface has a physical interface
Transport Name: Indicates the name of the protocol running over (or bound to) this interface
IPv4 and IPv6 information can be discovered by running a different command, ipconfig /all, as shown in Figure 4-5.
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FIGURE 4-5 Interface Configuration Information on Windows 11
The same basic information (IPv4 address, IPv6 address, subnet mask, etc.) is available here as the GUI, but additional information is also available. In particular:
The IPv6 DUID, described in Chapter 2, “Addresses”
The physical interface address
The default gateway
In most situations, starting Powershell and running ipconfig /all is the quickest way to find all the network information you need about a host. The ipconfig command can be used for more than showing current configuration information; it can also be used to
/release: Release DHCP-learned IPv4 addresses
/renew: Renew the DHCP-learned IPv4 addresses
/release6: Release DHCP-learned IPv6 addresses
/renew6: Renew DHCP-learned IPv6 addresses
/flushdns: Flush the local DNS cache
Two other pieces of network information available from Powershell are difficult to find in any GUI display: the local ARP cache and routing table. To see the local ARP cache, use the arp -a command, as shown in Figure 4-6.
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FIGURE 4-6 Showing the ARP Cache in Powershell
Each IP address is shown with its matching physical address in the table. Addresses marked dynamic were learned using ARP. Addresses marked static are embedded in the operating system software; for instance, the IP broadcast address (255.255.255.255) is always mapped to the physical interface broadcast address (ff-ff-ff-ff-ff-ff).
Figure 4-7 illustrates the Windows 11 host routing table, as displayed using the Get-NetRoute command from Powershell.
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FIGURE 4-7 The Windows Host Routing Table
Several fields are of interest in the output shown in Figure 4-7:
ifIndex: Indicates which interface to send packets through when following this route.
DestinationPrefix: Indicates the destination network.
NextHop: Identifies where to send packets to reach this destination; 0.0.0.0 means “this device” or the local host.
RouteMetric: Indicates the metric, or cost to reach this destination. Windows hosts use the hop count as a metric.
ifMetric: Indicates the default metric for routes reachable through this interface.