Reading IPConfig and Diagnosing Network Problems

Both Internet Service and Windows Networking rely upon the Internet Protocol being properly configured. The IPConfig utility tells us the various settings on any computer using Internet Protocol. This is a good place to start, when diagnosing any networking problem.

Please note that the examples shown here are from a computer setup in a workgroup, which is almost identical to a domain. There is one major difference for a domain; the DNS server entry, for a computer in a domain, should point to the IP address of the domain controller, as indicated in Windows XP / 2000 On A Domain.

This is a problem, as the ipconfig listing will not give a clue as to where the domain controller points (forwards its DNS queries). If you have DNS problems, in a computer on a domain, ipconfig will not help diagnose any such.

To get ipconfig data for immediate examination, simply type “ipconfig /all” into a command window. Only type the command into a command window – do not do Start – Run – “ipconfig /all…”.

If you want the data so it is easily compared between computers, you need to export the data into a text file.

  • Type “ipconfig /all >c:\ipconfig.txt” (less the “”) into a command window.
  • Then,
    • Type “notepad c:\ipconfig.txt” (less the “”) into the same command window, for immediate examination.
    • Or, copy file c:\ipconfig.txt to another computer, for comparative examination.

A Normal IPConfig

Here’s an example of IPConfig (“ipconfig /all”) from a pair of computers on a LAN.

Windows IP Configuration
        Host Name . . . . . . . . . . . . : PChuck1
        Primary Dns Suffix  . . . . . . . : 
        Node Type . . . . . . . . . . . . : Broadcast
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No
        DNS Suffix Search List. . . . . . : pchuck.net
Ethernet adapter Local Area Connection:
        Connection-specific DNS Suffix  . : 
        Description . . . . . . . . . . . : 3Com EtherLink XL 10/100 PCI For Complete PC Management NIC (3C905C-TX)
        Physical Address. . . . . . . . . : 00-04-76-D7-C5-6A
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.50
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 192.168.1.11
                                            192.168.1.33
        Lease Obtained. . . . . . . . . . : Wednesday, April 16, 2003 11:19:12
        Lease Expires . . . . . . . . . . : Wednesday, April 23, 2003 11:19:12

Windows IP Configuration
        Host Name . . . . . . . . . . . . : PChuck2
        Primary Dns Suffix  . . . . . . . : 
        Node Type . . . . . . . . . . . . : Hybrid
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No
        DNS Suffix Search List. . . . . . : pchuck.net
Ethernet adapter Local Area Connection:
        Connection-specific DNS Suffix  . : 
        Description . . . . . . . . . . . : 3Com EtherLink XL 10/100 PCI For Complete PC Management NIC (3C905C-TX)
        Physical Address. . . . . . . . . : 00-04-76-D7-76-BC
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.51
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 192.168.1.11
                                            192.168.1.33
        Primary WINS Server . . . . . . . : 192.168.1.1
        Lease Obtained. . . . . . . . . . : Wednesday, April 16, 2003 11:53:45
        Lease Expires . . . . . . . . . . : Wednesday, April 23, 2003 11:53:45

What does this tell us?

        Host Name . . . . . . . . . . . . : PChuck1

This is the name of the computer, as seen by Internet Protocol.

        Primary Dns Suffix  . . . . . . . : 
        DNS Suffix Search List. . . . . . : pchuck.net

Most small LANs don’t have a DNS server setup, so you probably won’t use DNS for name resolution. If you do have a DNS server (not the one which your ISP provides, either), you should setup both DHCP and DNS carefully.

        Node Type . . . . . . . . . . . . : Broadcast

The Node Type tells us how this computer identifies the address of another computer on the LAN. Broadcast is the best setting for a small LAN, although anything but Peer-Peer will work. If you do not have a WINS server, and you see Peer-Peer here, you do have a problem.

If you have a LAN with its own DNS server, you will want to setup your LAN, and the DNS server, properly.

        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes

If DHCP is enabled, this computer should get it’s IP settings from a DHCP server (either a NAT router / ICS Host, or a dedicated server running the DHCP service).

If Autoconfiguration is enabled, this computer did get its IP settings from a DHCP server. If DHCP is enabled, but Autoconfiguration is not enabled, a DHCP server was not available. If the latter, it is very likely that the computer now has an APIPA address, and may display the message “limited or no connectivity“.

        Physical Address. . . . . . . . . : 00-04-76-D7-C5-6A
        IP Address. . . . . . . . . . . . : 192.168.1.50
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 192.168.1.11
                                            192.168.1.33
        Primary WINS Server . . . . . . . : 192.168.1.1

These are the most basic settings. You must get the addressing right, before the other components will be of much use.

The Physical Address is the MAC address for this network card. If this is the Vendor Assigned address, it is unique for this device. All Vendor Assigned addresses are unique, for every device in the world. If this is a User Defined address, it was set using tools provided by the vendor. For NT compliant network hardware, this was likely the device properties wizard, accessed from Local Area Connection Properties in Network Connections.

The IP Address for each computer must be unique. Taking the IP Address and the Subnet Mask, and subnetting the IP address, we see that this subnet is 192.168.1.0/24, and the Host Address is 50. On any LAN segment, all hosts (computers) must have the same subnet, and all computers must have a different host address.

While the Subnet and Host addresses together determine which computers on a LAN can communicate, the Default Gateway determines if the computer can communicate with any hosts outside the subnet. The Default Gateway must be the IP address of another host, on that same subnet, that also connects outside the LAN. With no default gateway value, or with an invalid IP address here, your computer won’t have access outside the LAN.

Having one or more computers with APIPA addresses – 169.254.0.0/16 (169.254.0.0 / 255.255.0.0) could have various causes.

  • If you’re connecting 2 computers directly, using a cross-over cable, then the APIPA addresses are perfectly normal.
  • If you’re connecting a computer to an ICS server, or to a NAT router, and it’s getting a 169.254.x.x address, then either you have a physical network problem, or the DHCP server (ICS server) is disabled.

The DHCP Server identifies the network device that issued the IP settings to this computer. If you have two computers which can’t communicate, and they have incompatible IP settings, checking the DHCP Server might show settings from two different DHCP servers.

There are two possible reasons for having two different DHCP servers.

  • If you’re paying your ISP for two ip addresses, you may be getting two addresses on different subnets, which is a perfectly expectable situation for cable broadband. The solution for this may be to not use IP on your LAN.
  • You also might have an unknown (rogue) DHCP server on your LAN. In that case, knowing the IP addresses of both servers should help you identify each server.

The Physical Address, IP Address, Subnet Mask, and Default Gateway are settings which describe how this computer connects to the network. DNS Servers, on the other hand, provide the ability to resolve the IP address of another computer on the network.

WINS is a legacy Microsoft name resolution protocol, used with Windows NT V4.0, and Windows 2000 (aka Windows NT V5.0). With Windows XP (aka Windows NT V5.1), Microsoft elected to use DNS, as the rest of the world has been doing for a while. But we still have the possibility to use WINS built in to Windows XP.

If your host configuration specifies a WINS server, you better have one. If a WINS server is configured, and WINS is queried, Windows XP will wait for a query against it to timeout. Depending upon the value of Node Type, you will have various problems.

  • If Node Type is Broadcast, the WINS entry will be ignored.
  • If Node Type is Hybrid, name resolution by Broadcast will be tried only AFTER WINS resolution is tried and times out. This will significantly increase latency in many file sharing processes.
  • If Node Type is Mixed, name resolution by Broadcast will be tried first. If the requested computer does not respond to a Broadcast (maybe you typed in the name wrong), name resolution will try WINS next. The WINS query will have to timeout before reporting “name not found” aka “Error = 53”.
  • If Node Type is Peer-Peer, only the WINS server will be tried. This is a common problem on small LANS.
  • If Node Type is Unknown, it will be treated as Hybrid.

Note that any or all of the above settings can come from automatic configuration (the Network Setup Wizard), or manual configuration (the TCP/IP Properties wizard).

A Bridge

When you run the Network Setup Wizard, you may end up with a bridge. Bridges cause problems with file sharing, and with Internet service sharing. You can get a bridge from having any of the following:

  • Two network cards, connected to two different subnets.
  • Dialup Internet service, with a modem and a network card.
  • PPPoE Internet service, with a PPPoE modem and a network card.
  • One network card and a 1394 Firewire device.
Windows IP Configuration
        Host Name . . . . . . . . . . . . : MyComputer
        Primary Dns Suffix  . . . . . . . : 
        Node Type . . . . . . . . . . . . : Unknown
        IP Routing Enabled. . . . . . . . : Yes
        WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Network Bridge (Network Bridge):
        Connection-specific DNS Suffix  . : 
        Description . . . . . . . . . . . : MAC Bridge Miniport
        Physical Address. . . . . . . . . : 02-2F-CC-91-84-FF
        Dhcp Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : 192.168.0.1
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . :

If you don’t intentionally want a bridge, get rid of it. If you need a bridge, please refer to Steve Winograd PracticallyNetworked XP ICS – Network Bridge.

You can avoid ending up with a bridge, if you follow the advice from Microsoft How to prevent the Network Setup Wizard from creating a bridge in Windows XP.

IPV6
When you run the Network Setup Wizard, you may end up with IPV6, aka Automatic Tunneling, aka Teredo Tunneling.

Windows IP Configuration
        Host Name . . . . . . . . . . . . : PChuck1
        Primary Dns Suffix  . . . . . . . : 
        Node Type . . . . . . . . . . . . : Broadcast
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No
        DNS Suffix Search List. . . . . . : myhome.net
Ethernet adapter Local Area Connection:
        Connection-specific DNS Suffix  . : 
        Description . . . . . . . . . . . : 3Com EtherLink XL 10/100 PCI For Complete PC Management NIC (3C905C-TX)
        Physical Address. . . . . . . . . : 00-04-76-D7-E2-BA
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.50
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 10.201.99.11
                                            10.201.99.33
        Lease Obtained. . . . . . . . . . : Wednesday, April 16, 2003 11:19:12
        Lease Expires . . . . . . . . . . : Wednesday, April 23, 2003 11:19:12
Tunnel adapter Automatic Tunneling Pseudo-Interface:
        Connection-specific DNS Suffix  . : 
        Description . . . . . . . . . . . : Automatic Tunneling Pseudo-Interface
        Physical Address. . . . . . . . . : C0-A8-00-03
        Dhcp Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : fe80::5efe:192.168.1.50%2
        Default Gateway . . . . . . . . . : 
        DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1
                                            fec0:0:0:ffff::2%1
                                            fec0:0:0:ffff::3%1
        NetBIOS over Tcpip. . . . . . . . : Disabled

The presence of IPV6, aka Automatic / Teredo Tunneling, may hamper the diagnosis of your problems. Please remove IPV6 while we are working on your problems; if you truly need it, you can re install it later. You must remove IPV6.

A Hardware Firewall

This may become a common observance in the future.

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : NVIDIA nforce Networking Controller

This is a hardware firewall, sitting inside your computer. The nVidia nForce is probably the first, but surely not the last, device of this type.

IPConfig Command not recognised

And here’s an odd result. You type “ipconfig”, and get

‘ipconfig’ is not recognized as an internal or external command, operable program or batch file.

In this case, you have still more work to do. There are several possibilities.

  • Check the Path. The entry “;%systemroot%\system32” may be missing.
  • You may need to reload TCP/IP (if this is not Windows XP), or reset TCP/IP (if this is Windows XP).
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