مشاهده نسخه کامل
: Vahed
28-07-2007, 22:29
It’s probably happened to you at least once—you sit
down in front of the computer to browse the Web or
check email, only to discover that your system doesn’t appear
to be connected to the Internet.
That’s an easy conclusion to come to, but it’s a bit
more difficult to figure out exactly why you can’t connect
and what you should do to fix it. Windows XP includes
two network utilities, Ipconfig and Ping, that can help.
Although both are command-line utilities, both can be
enormously helpful in identifying the cause of and
solving a network problem.
Ipconfig
Whenever you’re having a problem connecting to
the Internet, the first step toward resolving the problem
is to verify that your system has a valid IP (Internet
Protocol) address. This is easily accomplished using
Ipconfig (IP Configuration), a utility that lets you determine
whether TCP/IP (Transmission Control
Protocol/Internet Protocol; a language that controls
communications among computers on the Internet) is
running and correctly configured on your computer.
To run Ipconfig, you need to first access a commandline
window, which you can do by clicking Start and then
Run, typing CMD, and pressing ENTER. In the command
line window, type IPCONFIG and press ENTER to
see basic IP configuration data for each network adapter
installed on your system. This information includes the
adapter’s IP address, subnet mask, and default gateway.
Most home computers are connected either directly
to a cable/DSL (Digital Subscriber Line) modem or to a
router (which in turn is connected to the cable/DSL
modem) and typically get their IP addresses automatically
from one of those devices (the one it’s directly
connected to) via DHCP (Dynamic Host Configuration
Protocol). When TCP/IP is correctly configured, you
should see entries under all three Ipconfig headings: IP
Address, Subnet Mask (almost always 255.255.255.0),
and Default Gateway. In most cases when there’s a
router on your network, the computer’s IP and default
gateway addresses will both begin with 192.168—only
the last numbers of the address should be different.
Identifying Problems
There are a number of warning signs in Ipconfig that
indicate an IP configuration problem. If Ipconfig reports
your network adapter’s IP address as 0.0.0.0 or if the address
starts with 169.254, it usually indicates that your
system requested an IP address but didn’t get one for
some reason, which does happen from time to time. To
manually issue a new address request, type IPCONFIG/
RELEASE to reset the connection; when the command
prompt reappears, type IPCONFIG/RENEW. In many
cases, this will resolve the connection problem, but another
option is to right-click the adapter’s icon in
Network Connections and choose Repair. This will not
only reset and renew the IP address request, but also disable
and re-enable the adapter itself.
If your adapter doesn’t list any IP information but instead
reports Media Disconnected, it probably means
your network cable has become detached or that the
router or cable/DSL modem at the other end of the cable
isn’t plugged in or powered on. (In the case of a wireless
network adapter, this message means that you’re not
connected to the wireless network.) You’ll need to rectify
these issues before attempting to obtain an IP address.
Ping
Ping is a simple utility that tests the network connection
between two computers. This makes it an extremely
valuable tool to help isolate a connectivity problem and
determine whether it lies with your equipment, your
ISP’s (Internet service provider’s) equipment, or somewhere
on the ISP’s network.
Once you’ve used Ipconfig to make sure your system’s
IP configuration is correct, the next step is to use
Ping to methodically test the connection along various
points along the link from your computer to the
Internet. As with Ipconfig, it’s best to launch a command
line window, so the results of the command stay
on your screen long enough for you to read them. If
you use a software firewall, it’s also important to disable
it before using Ping because the default configuration
of most software firewalls will suppress Ping
responses, rendering it useless as a diagnostic tool.
Step 1. The first link in the chain to ping is your computer’s
internal TCP/IP connection. You can do this by
typing PING, a space, and then 127.0.0.1. Press ENTER.
The address 127.0.0.1, also known as the loopback, is a
special address which is a stand-in for your computer’s
real IP address. Alternatively, you can enter your computer’s
actual IP address or localhost—all three are
equivalent. After you execute the Ping command, you
should receive four replies in rapid succession formatted
as follows: Reply from 127.0.0.1: bytes=32 time<1ms
TTL=128 followed by some summary information. (If
you ping your actual IP address, the response will come
from that address instead of the loopback.)
Step 2. The next link to test is the connection between
your computer and the router or the cable/DSL device it’s
connected to. In either case this device is known as your
default gateway—its IP address can be found under that
heading when you run Ipconfig. (If your system is connected
to a router, the address is usually 192.168.1.1 or
192.168.0.1, but if your system is connected directly to a
cable/DSL modem, it may be something else.) When you
ping your network’s default gateway, you should receive
four prompt replies from that address, much as you did
when you tested your system’s internal connection. If you
don’t get those replies and instead receive Destination
Host Unreachable or Request Timed out, it probably
means that the device is disconnected or malfunctioning.
Checking the network and power cables and/or restarting
the device will often clear up the problem.
Step 3. If you were testing the connection to a router in
the previous step, the next connection to test is the one to
your cable/DSL modem. (If your system is connected directly
to your cable/DSL modem, skip this step.) When a
cable/DSL modem is connected to a router instead of to a
PC, you can’t get its IP address via Ipconfig. The best way
to get it is to log in to your router’s administration console
and look it up on the router’s status screen. It’s usually
listed as the Internet or WAN address, but because
routers vary as to where they display this information,
check your device’s manual on how to find it.)
After you’ve located your cable/DSL device’s IP address,
ping it just as you did the previous addresses. If you don’t
get replies, check the network and power cables and
restart both your cable/DSL modem. If this doesn’t restore
your connection, a call to your ISP is probably warranted.
Step 4. After you’ve successfully pinged all the devices
on your premises, the final step is to try to ping an
address on the Internet. (Trying to access a Web page is
often a reliable indicator of connectivity, but it isn’t
conclusive because the problem could be with your
browser or the specific site.)
To verify that your system is reaching the Internet,
ping a Web site you frequently visit. It’s not necessary to
know the actual IP address of the site; using a friendly
name such as Yahoo! (
برای مشاهده محتوا ، لطفا وارد شوید یا ثبت نام کنید) is fine. Because
you’re only trying to verify a connection to the Internet,
not necessarily a specific site, you don’t need to include
www in the address; it doesn’t matter if you do include
it, though the reply might appear to come from a slightly
different address from the one you pinged depending on
how the site has been set up. To do so, at the command
prompt, type ping yahoo.com and press ENTER.
Many major Web sites intentionally don’t reply to
pings. If you don’t get a reply when pinging a site, check to
see whether the response includes the site’s numerical IP
address. If it does, this indicates your Internet connection
is working because that address must be looked up from a
DNS (Domain Name Server) on the Internet. If you don’t
get a reply to a ping command and the response doesn’t
include the IP address of the site you pinged, it probably
means your ISP is having network problems, and you’ll
need to get in touch with it
down in front of the computer to browse the Web or
check email, only to discover that your system doesn’t appear
to be connected to the Internet.
That’s an easy conclusion to come to, but it’s a bit
more difficult to figure out exactly why you can’t connect
and what you should do to fix it. Windows XP includes
two network utilities, Ipconfig and Ping, that can help.
Although both are command-line utilities, both can be
enormously helpful in identifying the cause of and
solving a network problem.
Ipconfig
Whenever you’re having a problem connecting to
the Internet, the first step toward resolving the problem
is to verify that your system has a valid IP (Internet
Protocol) address. This is easily accomplished using
Ipconfig (IP Configuration), a utility that lets you determine
whether TCP/IP (Transmission Control
Protocol/Internet Protocol; a language that controls
communications among computers on the Internet) is
running and correctly configured on your computer.
To run Ipconfig, you need to first access a commandline
window, which you can do by clicking Start and then
Run, typing CMD, and pressing ENTER. In the command
line window, type IPCONFIG and press ENTER to
see basic IP configuration data for each network adapter
installed on your system. This information includes the
adapter’s IP address, subnet mask, and default gateway.
Most home computers are connected either directly
to a cable/DSL (Digital Subscriber Line) modem or to a
router (which in turn is connected to the cable/DSL
modem) and typically get their IP addresses automatically
from one of those devices (the one it’s directly
connected to) via DHCP (Dynamic Host Configuration
Protocol). When TCP/IP is correctly configured, you
should see entries under all three Ipconfig headings: IP
Address, Subnet Mask (almost always 255.255.255.0),
and Default Gateway. In most cases when there’s a
router on your network, the computer’s IP and default
gateway addresses will both begin with 192.168—only
the last numbers of the address should be different.
Identifying Problems
There are a number of warning signs in Ipconfig that
indicate an IP configuration problem. If Ipconfig reports
your network adapter’s IP address as 0.0.0.0 or if the address
starts with 169.254, it usually indicates that your
system requested an IP address but didn’t get one for
some reason, which does happen from time to time. To
manually issue a new address request, type IPCONFIG/
RELEASE to reset the connection; when the command
prompt reappears, type IPCONFIG/RENEW. In many
cases, this will resolve the connection problem, but another
option is to right-click the adapter’s icon in
Network Connections and choose Repair. This will not
only reset and renew the IP address request, but also disable
and re-enable the adapter itself.
If your adapter doesn’t list any IP information but instead
reports Media Disconnected, it probably means
your network cable has become detached or that the
router or cable/DSL modem at the other end of the cable
isn’t plugged in or powered on. (In the case of a wireless
network adapter, this message means that you’re not
connected to the wireless network.) You’ll need to rectify
these issues before attempting to obtain an IP address.
Ping
Ping is a simple utility that tests the network connection
between two computers. This makes it an extremely
valuable tool to help isolate a connectivity problem and
determine whether it lies with your equipment, your
ISP’s (Internet service provider’s) equipment, or somewhere
on the ISP’s network.
Once you’ve used Ipconfig to make sure your system’s
IP configuration is correct, the next step is to use
Ping to methodically test the connection along various
points along the link from your computer to the
Internet. As with Ipconfig, it’s best to launch a command
line window, so the results of the command stay
on your screen long enough for you to read them. If
you use a software firewall, it’s also important to disable
it before using Ping because the default configuration
of most software firewalls will suppress Ping
responses, rendering it useless as a diagnostic tool.
Step 1. The first link in the chain to ping is your computer’s
internal TCP/IP connection. You can do this by
typing PING, a space, and then 127.0.0.1. Press ENTER.
The address 127.0.0.1, also known as the loopback, is a
special address which is a stand-in for your computer’s
real IP address. Alternatively, you can enter your computer’s
actual IP address or localhost—all three are
equivalent. After you execute the Ping command, you
should receive four replies in rapid succession formatted
as follows: Reply from 127.0.0.1: bytes=32 time<1ms
TTL=128 followed by some summary information. (If
you ping your actual IP address, the response will come
from that address instead of the loopback.)
Step 2. The next link to test is the connection between
your computer and the router or the cable/DSL device it’s
connected to. In either case this device is known as your
default gateway—its IP address can be found under that
heading when you run Ipconfig. (If your system is connected
to a router, the address is usually 192.168.1.1 or
192.168.0.1, but if your system is connected directly to a
cable/DSL modem, it may be something else.) When you
ping your network’s default gateway, you should receive
four prompt replies from that address, much as you did
when you tested your system’s internal connection. If you
don’t get those replies and instead receive Destination
Host Unreachable or Request Timed out, it probably
means that the device is disconnected or malfunctioning.
Checking the network and power cables and/or restarting
the device will often clear up the problem.
Step 3. If you were testing the connection to a router in
the previous step, the next connection to test is the one to
your cable/DSL modem. (If your system is connected directly
to your cable/DSL modem, skip this step.) When a
cable/DSL modem is connected to a router instead of to a
PC, you can’t get its IP address via Ipconfig. The best way
to get it is to log in to your router’s administration console
and look it up on the router’s status screen. It’s usually
listed as the Internet or WAN address, but because
routers vary as to where they display this information,
check your device’s manual on how to find it.)
After you’ve located your cable/DSL device’s IP address,
ping it just as you did the previous addresses. If you don’t
get replies, check the network and power cables and
restart both your cable/DSL modem. If this doesn’t restore
your connection, a call to your ISP is probably warranted.
Step 4. After you’ve successfully pinged all the devices
on your premises, the final step is to try to ping an
address on the Internet. (Trying to access a Web page is
often a reliable indicator of connectivity, but it isn’t
conclusive because the problem could be with your
browser or the specific site.)
To verify that your system is reaching the Internet,
ping a Web site you frequently visit. It’s not necessary to
know the actual IP address of the site; using a friendly
name such as Yahoo! (
برای مشاهده محتوا ، لطفا وارد شوید یا ثبت نام کنید) is fine. Because
you’re only trying to verify a connection to the Internet,
not necessarily a specific site, you don’t need to include
www in the address; it doesn’t matter if you do include
it, though the reply might appear to come from a slightly
different address from the one you pinged depending on
how the site has been set up. To do so, at the command
prompt, type ping yahoo.com and press ENTER.
Many major Web sites intentionally don’t reply to
pings. If you don’t get a reply when pinging a site, check to
see whether the response includes the site’s numerical IP
address. If it does, this indicates your Internet connection
is working because that address must be looked up from a
DNS (Domain Name Server) on the Internet. If you don’t
get a reply to a ping command and the response doesn’t
include the IP address of the site you pinged, it probably
means your ISP is having network problems, and you’ll
need to get in touch with it