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Windows 8 includes many tools for troubleshooting and testing TCP/IP
connectivity. The following sections look at automated diagnostics,
basic tests that you should perform whenever you install or modify a
computer’s network settings, and techniques for resolving difficult
networking problems involving DHCP and DNS. The final section shows you
how to perform detailed network diagnostics testing.
Diagnosing and Resolving Network Connection Problems
Occasionally, network cables can become unplugged or the network
adapter might experience a problem that temporarily prevents it from
working. After you plug the cable back in or solve the adapter problem,
the connection should automatically reconnect. You can diagnose network
connection problems by pressing and holding or right-clicking the
Network notification icon on the taskbar and tapping or clicking
Troubleshoot Problems.
Windows Network Diagnostics then tries to identify the problem. Another way to start Windows Network Diagnostics is to press and hold or right-click the connection in Network Connections and then tap or click Diagnose.
As shown in Figure 1,
a list of possible solutions is provided if identifiable configuration
problems are detected. Some solutions provide automated fixes that can
be executed by tapping or clicking the solution. Other solutions require
manual fixes, such as resetting a network router or a broadband modem.
If your actions don’t fix the problem, refer to other appropriate parts
of this troubleshooting section.
Diagnosing and Resolving Internet Connection Problems
Because services, protocols, and configuration settings have so many interdependencies, troubleshooting
network problems can be difficult. Fortunately, Windows 8 includes a
powerful network diagnostics tool for pinpointing problems that relate
to the following:
-
General network connectivity problems -
Internet service settings for email, newsgroups, and proxies -
Settings for modems, network clients, and network adapters -
DNS, DHCP, and WINS configuration -
Default gateways and IP addresses
In Network And Sharing Center, you can diagnose connection problems
by tapping or clicking Troubleshoot Problems and then tapping or
clicking a troubleshooter to run, such as Network Adapter, Incoming
Connections, or Internet Connection.
The troubleshooter then tries to identify the problem. If
identifiable configuration problems exist, a list of possible solutions
is provided. Some solutions provide automated fixes that can be executed
by tapping or clicking the solution. Other solutions require manual
fixes, such as resetting a network router or a broadband modem. If your actions don’t fix the problem, refer to other appropriate parts of this troubleshooting section.
Performing Basic Network Tests
Whenever you install a new computer or make configuration changes to a
computer’s network settings, you should test the configuration. The
most basic TCP/IP test is to use the Ping command to test the computer’s connection to the network. To use it, type ping <host>
at the command prompt, where <host> is either the computer name or the IP address of the host computer you’re trying to reach.
With Windows 8, you can use the Ping command in the following ways to test the configuration:
-
Try to ping IP addresses
If the computer is configured correctly and the host you’re trying to
reach is accessible to the network, Ping should receive a reply,
provided that pinging is allowed by the computer’s firewall. If Ping
can’t reach the host or is blocked by a firewall, Ping times out. -
On domains that use WINS, try to ping NetBIOS computer names
If NetBIOS computer names are resolved correctly by Ping, the NetBIOS
facilities, such as WINS, are correctly configured for the computer. -
On domains that use DNS, try to ping DNS host names If fully qualified DNS host names are resolved correctly by Ping, DNS name resolution is configured properly.
You might also want to test network browsing for the computer. If the
computer is a member of a Windows 8 domain and computer browsing is
enabled throughout the domain, log on to the computer and then use File
Explorer or Network Explorer to browse other computers in the domain.
Afterward, log on to a different computer in the domain and try to
browse the computer you just configured. These tests tell you whether
DNS resolution is being handled properly in the local environment. If
you can’t browse, check the configuration of the DNS services and
protocols.
Note
REAL WORLD Access to network
resources in Network Explorer is dependent on the Computer Browser
service and the network discovery settings. The Computer Browser service
is responsible for maintaining a list of computers on a network. If the
service is stopped or isn’t working properly, a computer won’t see
available resources in Network Explorer. You can check the status of the
Computer Browser service in Computer Management. Expand Services And
Applications, and then select Services in the left pane. The status of
the Computer Browser service should be Started. If the status is blank,
the service isn’t running and should be started.
In some cases, the Computer Browser service might be running
normally, but there might not be an updated list of resources in Network
Explorer. This can happen because the service performs periodic updates
of the resource list rather than checking continuously for updates. If a
resource you want to use isn’t listed, you can wait for it to become
available (which should take less than 15 minutes in most cases), or you
can connect to the resource directly by using the Universal Naming
Convention (UNC) name or IP address of the resource.
In some cases, discovering and sharing might be set to block network
discovery. You need to allow network discovery to resolve this by
following these steps:
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In Control Panel, tap or click View Network Status And Tasks under the Network And Internet heading. -
In Network And Sharing Center, in the left pane, tap or click Change Advanced Sharing Settings. -
You’ll then see options for configuring the computer’s sharing and
network discovery settings for each network profile. Manage the settings
for each profile, as appropriate. For example, if the network
discovered is disabled for a profile and should be enabled, tap or click
the related Turn On Network Discovery option. -
Tap or click Save Changes.
Resolving IP Addressing Problems
The current IP address settings of a computer can be obtained . If a computer is having problems
accessing network resources or communicating with other computers, an IP
addressing problem might exist. Take a close look at the IP address
currently assigned, as well as other IP address settings, and use the
following pointers to help in your troubleshooting:
-
If the IPv4 address currently assigned to the computer is in the range 169.254.0.1 to 169.254.255.254, the computer is using Automatic Private IP Addressing (APIPA).
An automatic private IP address is assigned to a computer when it is
configured to use DHCP and its DHCP client cannot reach a DHCP server.
When using APIPA, Windows 8 will periodically check for a DHCP server to
become available. If a computer doesn’t eventually obtain a dynamic IP
address, this usually means the network connection has a problem. Check
the network cable and, if necessary, trace the cable back to the switch
or hub it connects to. -
If the IPv4 address and the subnet mask of the computer are currently
set as 0.0.0.0, the network is either disconnected or someone attempted
to use a static IP address that duplicated another IP address already
in use on the network. In this case, you should access Network
Connections and determine the state of the connection. If the
connection is disabled or disconnected, this status should be shown.
Press and hold or right-click the connection, and then tap or click
Enable or Repair. If the connection is already enabled, you need to
modify the IP address settings for the connection. -
If the IP address is dynamically assigned, check to be sure that
another computer on the network isn’t using the same IP address. You can
do this by disconnecting the network cable for the computer that you
are troubleshooting and pinging the IP
address in question from another computer. If you receive a response
from the Ping command, you know that another computer is using the IP address. This computer probably has an improper static IP address or a reservation that isn’t set up properly. -
If the IP address appears to be set correctly, check the network
mask, gateway, DNS, and WINS settings by comparing the network settings
of the computer you are troubleshooting
with those of a computer that is known to have a good network
configuration. One of the biggest problem areas is the network mask.
When subnetting is used, the network mask for one area of the network
might be very similar to that of another area. For example, the network
mask in one IPv4 area might be 255.255.255.240, and it might be
255.255.255.248 in another IPv4 area.
Releasing and Renewing DHCP Settings
DHCP servers can assign many network configuration settings
automatically. These include IP addresses, default gateways, primary and
secondary DNS servers, primary and secondary WINS servers, and more.
When computers use dynamic addressing, they are assigned a lease on a
specific IP address. This lease is good for a specific time period and
must be renewed periodically. When the lease needs to be renewed, the
computer contacts the DHCP server that provided the lease. If the server
is available, the lease is renewed and a new lease period is granted.
You can also renew leases manually on individual computers or by using
the DHCP server itself.
Problems can occur during the lease assignment and renewal process
that prevent network communications. If the server isn’t available and
cannot be reached before a lease expires, the IP address can become
invalid. If this happens, the computer might use the alternate IP
address configuration to set an alternate address, which in most cases
has settings that are inappropriate and prevent proper communications.
To resolve this problem, you need to release and then renew the DHCP
lease.
Another type of problem occurs when users move around to various
offices and subnets within an organization. In being moved from location
to location, their computers might obtain DHCP settings from the wrong
server. When the users return to their offices, the computers might seem
sluggish or perform incorrectly due to the settings assigned by the
DHCP server at another location. If this happens, you need to release
and then renew the DHCP lease.
You can release and renew DHCP leases by completing the following tasks:
-
In Network And Sharing Center, in the left pane, tap or click Change Adapter Settings. -
In Network Connections, press and hold or right-click the connection you want to work with, and then tap or click Diagnose. -
After Windows Network Diagnostics tries to identify the problem, a
list of possible solutions is provided. If the computer has one or more
dynamically assigned IP addresses, one of the solutions should be
Automatically Get New IP Settings. Tap or click this option.
You can also follow these steps to use the Ipconfig command to release and renew settings:
-
Open an elevated command prompt. One way to do this is to type cmd
in the Apps Search box, press and hold or right-click Command Prompt on
the Apps screen, and then tap or click Run As Administrator. -
To release the current settings for all network adapters, type ipconfig /release at the command line. Then renew the lease by typing ipconfig /renew. -
To only renew a DHCP lease for all network adapters, type ipconfig /renew at the command line. -
You can check the updated settings by typing ipconfig /all at the command line.
Note
REAL WORLD If you don’t release the old DHCP
settings before trying to renew the DHCP settings, the computer will
try to renew the settings on the network to which it was last connected.
If the computer is on a new network, the computer might not be able to
establish a connection to the server or device that assigned the DHCP
settings previously.
If a computer has multiple network adapters and you want to work with
only one or a subset of the adapters, you can do this by specifying all
or part of the connection name after the ipconfig /renew or ipconfig
/release command. Use the asterisk as a wildcard character to match any
characters in a connection’s name. For example, if you want to renew the
lease for all connections with names starting with Loc, you can type
the command ipconfig /renew Loc*. If you want to release the settings for all connections containing the word Network, you can type the command ipconfig /release *Network*.
Registering and Flushing DNS
The DNS resolver
cache maintains a history of DNS lookups that have been performed when a
user accesses network resources using TCP/IP. This cache contains
forward lookups, which provide host-name-to-IP-address resolution, and
reverse lookups, which provide IP-address-to-host-name resolution. Once a
DNS entry is stored in the resolver cache for a particular DNS host,
the local computer no longer has to query external servers for DNS
information on that host. This enables the computer to resolve DNS
requests locally, which provides a quicker response.
The period of time in which entries are stored in the resolver cache
depends on the Time to Live (TTL) value assigned to the record by the
originating server. To view current records and see the remaining TTL
value for each record, in an elevated command prompt, type ipconfig /displaydns.
These values are given as the number of seconds that a particular
record can remain in the cache before it expires. These values are
continually being counted down by the local computer. When the TTL value
reaches 0, the record expires and is removed from the resolver cache.
Occasionally, you’ll find that the resolver cache needs to be cleared
to remove old entries and enable computers to check for updated DNS
entries before the normal expiration and purging process takes place.
Typically, this happens because server IP addresses have changed, and
the current entries in the resolver cache point to the old addresses
rather than the new ones. Sometimes the resolver cache itself can become
out of sync, particularly when DHCP has been misconfigured.
Note
REAL WORLD Skilled
administrators know that several weeks in advance of the actual change,
they should start to decrease the TTL values for DNS records that are
going to be changed. Typically, this means reducing the TTL from a
number of days (or weeks) to a number of hours, which allows for quicker
propagation of the changes to computers that have cached the related
DNS records. Once the change is complete, administrators should restore
the original TTL value to reduce renewal requests.
In most cases, you can resolve problems with the DNS resolver cache
by flushing the cache or reregistering DNS. When you flush the resolver
cache, all DNS entries are cleared out of the cache and new entries are
not created until the next time the computer performs a DNS lookup on a
particular host or IP address. When you reregister DNS, Windows 8
attempts to refresh all current DHCP leases and then performs a lookup
on each DNS entry in the resolver cache. By looking up each host or IP
address again, the entries are renewed and reregistered in the resolver
cache. You’ll generally want to flush the cache completely and allow the
computer to perform lookups as needed. Reregister DNS only when you
suspect that there are problems with DHCP and the DNS resolver cache.
You can use the Ipconfig command to flush and reregister entries in the DNS resolver cache by following these steps:
-
Open an elevated command prompt. One way to do this is to type cmd
in the Apps Search box, press and hold or right-click Command Prompt on
the Apps screen, and then tap or click Run As Administrator. -
To clear out the resolver cache, type ipconfig /flushdns at the command line. -
To renew DHCP leases and reregister DNS entries, type ipconfig /registerdns at the command line. -
When the tasks are complete, you can check your work by typing ipconfig /displaydns at the command line.
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