After you’ve checked the hardware, you can run several command-line tools to aid in troubleshooting connectivity issues. A good first step is to ping the target host, which can tell you if the remote host is reachable and how long it takes to reach it:

> ping <HostNameOrIP>

Here are some of the status messages you can receive from ping:

Reply

The host was reachable.

Request timed out

The target host either did not respond or there is no host configured with the corresponding IP address. You may also see this message if there is a lot of network latency between the two endpoints. You can work around this by using the -w option with ping and specifying the number of milliseconds to wait for each reply.

Unknown host

If you used a DNS name in the ping command, this indicates that the DNS name was not resolvable by the DNS client.

Destination unreachable

The ICMP traffic could not reach the network of the target host. This is often due to a routing problem on an intermediate router or a router being down.

If you’ve pinged a host and the request timed out or the host was unreachable, a good tool to try next is tracert, which attempts to trace a route from the source computer to the destination computer.

> tracert <HostNameOrIP>

This command shows you the path your data takes to get to the destination. If there are connectivity problems with a remote host, this command shows where the problem occurs.

If everything checks out, next run the netdiag command on the target system. netdiag provides a wealth of information about various network settings configured on the system along with information about DNS, Kerberos, and Active Directory connectivity. Use the /debug option to view detailed output. If you suspect authentication (Kerberos) to be a potential issue, run the kerbtray utility to ensure you have functioning Kerberos tickets.

If you are still having network problems, a good last step is to look at the network traffic to see if you can spot any obvious errors being transmitted.

1. From the Control Panel open the Network Connections applet.
2. Right-click the network connection you want to disable and select Disable.

Using a command-line interface

You would think that it would be straightforward to disable a connection from the command line, but unfortunately that is not the case. In fact, the netsh command supports disabling connections, but only non-LAN interfaces, which is very disappointing.

But all is not lost! There is an alternative if you really must have a way to disable connections from the command line. The devcon.exe tool is the command-line alternative to the Device Manager interface and comes with the Driver Development Kit (DDK). You can download it separately by viewing MS KB 311272 (http://support.microsoft.com/default.aspx?scid=311272).

Once you have it downloaded, run this command to get a list of all network devices:

> devcon listclass net

This displays the list of devices in two columns. The left column contains the hardware ID for each device and the right column contains the description for the device.

After you’ve found the device you want to disable, run the following command:

> devcon disable =net <HardwareID>

For example:

> devcon disable =net PCI\VEN_14B9^&DEV_A504^&SUBSYS_500014B9^&REV_00

There are a couple of important things I need to point out. First, if the hardware ID contains any ampersands (&), you have to escape them using a caret (^). Otherwise, the CMD session will interpret everything after the first & as another command and devcon will attempt to match any hardware ID that matches the string up until the first &. This can be dangerous because it can cause you to disable devices you didn’t intend to.

Second, if the hardware ID contains two backslashes, remove the second backslash and everything following it. For example, if the listall command returned this for a device I wanted to disable:

PCI\VEN_14B9&DEV_A504&SUBSYS_500014B9&REV_00\4&39A85202&0&10F0: Cisco Systems PC I Wireless LAN Adapter

I would need to use this as the hardware ID (including the carets):

PCI\VEN_14B9^&DEV_A504^&SUBSYS_500014B9^&REV_00

Many servers these days come with two network adapters installed to avoid a single point of failure with the network connection. Generally, keep one connection active and use the other as a back up. There are a couple of ways to do this. One is to simply disable one of the connections and manually enable it if the primary fails. Since you probably won’t have network connectivity after the primary adapter fails, you’ll need another way to access the server, such as an out-of-band console connection of some type.

Another way to do this is to use a feature that many hardware vendors support called teaming. With teaming, both adapters are used to form a virtual adapter. If the primary adapter becomes unavailable, the backup takes over automatically. (See your hardware vendor for more details.) The problem with teaming is that, depending on the implementation, it can be unreliable and ultimately cause more configuration headaches than it is worth. I recommend testing teaming configurations thoroughly before implementing them in production.

1. From the Control Panel, open the Network Connections applet.
2. Open the network connection for which you want to view the settings.
3. Click the Properties button.
4. Click the Configure button to view network adapter properties. Or double-click Internet Protocol (TCP/IP) to view network configuration settings.

Using a command-line interface

To view the list of connections and network configuration on the local machine, run the following command:

> ipconfig /all

To view this information on a remote machine, use the Sysinternals psexec command:

> psexec \\<ServerName> -u administrator -p MyPass ipconfig /all

Another command you can use to view network configuration information is netsh, as shown here:

> netsh int ip show config

Using VBScript

' This code displays the network configuration for all connections.
' ------ SCRIPT CONFIGURATION ------
strComputer = "."
' ------ END CONFIGURATION ---------
set objWMI = GetObject("winmgmts:\\" & strComputer & "\root\cimv2")
set colNAs = objWMI.InstancesOf("Win32_NetworkAdapter")
for each objNA in colNAs
    Wscript.Echo objNA.Name
    Wscript.Echo "  Description:  " & objNA.Description
    Wscript.Echo "  Product Name: " & objNA.ProductName
    Wscript.Echo "  Manufacturer: " & objNA.Manufacturer
    Wscript.Echo "  Adapter Type: " & objNA.AdapterType
    Wscript.Echo "  AutoSense:    " & objNA.AutoSense
    Wscript.Echo "  MAC Address:  " & objNA.MACAddress
    Wscript.Echo "  Maximum Speed:" & objNA.MaxSpeed
    Wscript.Echo "  Conn Status:  " & objNA.NetConnectionStatus
    Wscript.Echo "  Service Name: " & objNA.ServiceName
    Wscript.Echo "  Speed:        " & objNA.Speed

    set colNACs = objWMI.ExecQuery(" select * from " & _
                                   " Win32_NetworkAdapterConfiguration " & _
                                   "  where Index = " & objNA.Index)
    ' There should only be one item in colNACs
    for each objNAC in colNACs
       if IsArray(objNAC.IPAddress) then
          for each strAddress in objNAC.IPAddress
             Wscript.Echo "  Network Addr: " & strAddress
          next
       end if
       Wscript.Echo "  IP Metric:    " & objNAC.IPConnectionMetric
       Wscript.Echo "  IP Enabled:   " & objNAC.IPEnabled
       Wscript.Echo "  Filter:       " & objNAC.IPFilterSecurityEnabled
       Wscript.Echo "  Port Security:" & objNAC.IPPortSecurityEnabled
       if IsArray(objNAC.IPSubnet) then
          for each strAddress in objNAC.IPSubnet
             Wscript.Echo "  Subnet Mask:  " & strAddress
          next
       end if
       if IsArray(objNAC.DefaultIPGateway) then
          for each strAddress in objNAC.DefaultIPGateway
             Wscript.Echo "  Gateway Addr: " & strAddress
          next
       end if
       Wscript.Echo "  Database Path:" & objNAC.DatabasePath
       Wscript.Echo "  DHCP Enabled: " & objNAC.DHCPEnabled
       Wscript.Echo "  Lease Expires:" & objNAC.DHCPLeaseExpires
       Wscript.Echo "  Lease Obtained: " & objNAC.DHCPLeaseObtained
       Wscript.Echo "  DHCP Server:  " & objNAC.DHCPServer
       Wscript.Echo "  DNS Domain:   " & objNAC.DNSDomain
       Wscript.Echo "  DNS For WINS: " & objNAC.DNSEnabledForWINSResolution
       Wscript.Echo "  DNS Host Name:" & objNAC.DNSHostName
       if IsArray(objNAC.DNSDomainSuffixSearchorder) then
          for each strName in objNAC.DNSDomainSuffixSearchOrder
             Wscript.Echo "  DNS Suffix Search Order: " & strName
          next
       end if
       if IsArray(objNAC.DNSServerSearchOrder) then
          for each strName in objNAC.DNSServerSearchOrder
             Wscript.Echo "  DNS Server Search Order: " & strName
          next
       end if
       Wscript.Echo "  Domain DNS Reg Enabled: " & _
                       objNAC.DomainDNSRegistrationEnabled
       Wscript.Echo "  Full DNS Reg Enabled: " & _
                       objNAC.FullDNSRegistrationEnabled
       Wscript.Echo "  LMHosts Lookup:      " & objNAC.WINSEnableLMHostsLookup
       Wscript.Echo "  WINS Lookup File:    " & objNAC.WINSHostLookupFile
       Wscript.Echo "  WINS Scope ID:       " & objNAC.WINSScopeID
       Wscript.Echo "  WINS Primary Server: " & objNAC.WINSPrimaryServer
       Wscript.Echo "  WINS Secondary:      " & objNAC.WINSSecondaryServer
    next

    WScript.Echo
next

There are several different ways to get at the host network configuration, as shown in the Solution section. And since the scripting solution used WMI, there is yet another way using wmic. Here are two commands that display some of the properties of the Win32_NetworkAdapter and Win32_NetworkAdapterConfiguration WMI clas-ses, respectively:

> wmic nic list brief
> wmic nicconfig list brief

A dhcp server can feed all network configuration data to the clients. The configuration file is /etc/dhcpd.conf. Here is a sample configuration:

# /etc/dhcpd.conf

default-lease-time 259200;

max-lease-time 518400;

subnet 192.168.1.0 netmask 255.255.255.0 {

   option subnet-mask 255.255.255.0;

   option broadcast-address 192.168.1.255;

   option routers 192.168.1.1;

   option domain-name "test.net";

   range 192.168.1.50 192.168.1.100;

   option domain-name-servers 152.163.199.56, 198.83.210.28;

}

This is pretty straightforward. The lease times are in seconds, so the minimum and maximum in this example are three days and six days. "Option routers" points to your Internet gateway, or the gateway to the subnet. A pool of 50 addresses is made available in the "range." The name servers are either your own private caching server or servers, or the name servers at your ISP.

This example uses private, nonroutable IPv4 (Internet Protocol Version 4) addresses. Here are the private IPv4 address classes, in both dotted-quad and Classless Inter-Domain Routing (CIDR) notation:

10.0.0.0     - 10.255.255.255  (10/8)

172.16.0.0   - 172.31.255.255  (172.16/12)

192.168.0.0  - 192.168.255.255 (192.168/16)

These are for use on private networks, so you’ll select your subnet ranges from these.