10 Ways to Troubleshoot DNS Resolution

Issues

by David Davis [Published on 17 June 2009 / Last Updated on 17 June 2009]

10 different ways to troubleshoot DNS resolutions issues.

Introduction

We all need proper DNS resolution for our network applications. When it this is not working,

what do you do? Let us find out

Lets face it, when DNS resolution is not working, using anything on your computer that has to do with networking is painful because there is good chance it will not work. DNS really is

not a nice feature of a network, it is a requirement. As a network admin, I have heard the alarming cry of end users moaning that the network is down, when it would be the cause of

the DNS servers. In these cases I assure them that the network is up and running fine but it is

the DNS servers that are down! As you can imagine, that does not go over very well with

them because to an end user, it is all the same thing. DNS is the network (not that they know what DNS is anyway).

So how do you troubleshoot this critical network infrastructure service when you are on an

end user PC (or your PC) and DNS is not resolving a DNS name? Here are the 10 tips and

tricks that I recommend you try to get DNS working again

1. Check for network connectivity

Many times, if you open your web browser, go to a URL, and that URL fails to bring up a

website, you might erroneously blame DNS. In reality, the issue is much more likely to be

caused by your network connectivity. This is especially true if you are using wireless

networking on a laptop. With wireless security protocols, the key will be periodically

renegotiated or the signal strength will fade, causing a loss of network connectivity. Of

course, you can lose network connectivity on any type of network.

In other words, before blaming DNS for your problems, start troubleshooting by checking

OSI Layer 1 Physical first and then check your network connectivity. Here you should find a wireless connection with a valid Internet connection.

Figure 1: Good Wireless Network Connection

Notice how the Access is Local and Internet. If it just said Local then you do not have a valid network address (you only have a private APIPA that starts with 169.x.x.x).

This brings me to my next point. Make sure that you have a valid IP address on your network.

You can check this out by going to View Status on the screen above and then to Details, you

can check your IP address and verify your DNS Server IP addresses. Again, if you have a

169.x.x.x IP address you will never get to the Internet. Here is what it looks like:

Figure 2: Verifying your IP address and DNS Server IP addresses

2. Verify your DNS server IP addresses are correct and in

order

Once you know that you have network connectivity and a valid IP address, let us move on to

digging deeper into DNS by verifying that your DNS Server IP addresses are correct and are

in the right order.

If you look at Figure 2 above, you can see the IPv4 DNS Server IP addresses. Notice that

these are both on my local LAN / subnet so that I can access them even if my default gateway

is down. This is how it works on most enterprise networks. However, your DNS servers do

not always have to be on your subnet. In fact, with most ISPs, the DNS Server IPs would not

even be on the same subnet as the default gateway.

In most home/SMB router configurations, they do not have their own DNS servers and the

SMB router is proxying DNS to the real DNS Servers. In that case, your DNS Server IP

address may be the same as your router.

Finally, make sure that your DNS Servers are in the right order. In my case, with the graphic

in Figure 2, my local DNS Server is 10.0.1.20. It is configured to forward any names that it

cannot resolve to 10.0.1.1, my local router. That router is proxying DNS to my ISPs DNS Servers. I can look up those DNS Servers on my router, shown below in Figure 3.

Figure 3: My local DNS Servers, received from my ISP via DHCP

That brings me to two more points. First, make sure that your DNS Servers are in the right

order. If you have a local DNS Server, like I do, and you are looking up a local DNS name,

you want your PC client to lookup that local DNS name in the local DNS Server FIRST,

before the Internet DNS Server. Thus, your local DNS server needs to be first in your DNS

settings as these DNS Server IPs are in the order that they will be used.

Secondly, you should be able to ping the IP address of your ISPs DNS Servers. So, just as my DNS servers are listed above on my router, I can verify that I can ping them even from

my local PC:

Figure 4: Pinging my ISPs DNS Server

Notice how the response time from the ping to my ISPs DNS Server is horrible. This could cause slow DNS lookups or even failure if it takes too long for the DNS server to respond.

3. Ping the IP address of the host you are trying to get to

(if it is known)

A quick way to prove that it is a DNS issue and not a network issue is to ping the IP address

of the host that you are trying to get to. If the connection to the DNS name fails but the

connection to the IP address succeeds, then you know that your issue has to do with DNS.

I know that if your DNS Server is not functioning then it could be hard to figure out what the

IP address is that you want to connect to. Thus, to carry out this test, you would have to have

a network diagram or, like many network admins do, just have the IP address of a common

host memorized.

If this works, until the DNS server is available again, you could manually put an entry in your

hosts file to map the IP to the hostname.

4. Find out what DNS server is being used with nslookup

You can use the nslookup command to find out a ton of information about your DNS

resolution. One of the simple things to do is to use it to see what DNS server is providing you

an answer and which DNS server is NOT. Here is my nslookup of

www.WindowsNetworking.com

Figure 5: nslookup output

Notice, in Figure 5, how my local DNS server failed to respond but my ISPs DNS server did provide me a non-authoritative answer, meaning that it does not host the domain but can provide a response.

You can also use nslookup to compare the responses from different DNS servers by manually

telling it which DNS server to use.

5. Check your DNS suffix

If you are looking up a local host on a DNS server that your PC is a member of, you might be

connecting to a host and not using the FQDN (fully qualified DNS name) and counting on the

DNS suffix to help out. For example, if I were to connect to server1, the DNS server could have multiple entries for that DNS name. You should have your network adaptor configured

with the connection specific DNS suffix, as shown on the first line on the graphic above,

labeled Figure 1. Notice how in that graphic my DNS suffix is wiredbraincoffee.com.

Whenever I enter just a DNS name like server1, the DNS suffix will be added on the end of

it to make it server1.wiredbraincoffee.com.

You should verify that your DNS suffix is correct.

6. Make sure that your DNS settings are configured to pull

the DNS IP from the DHCP server

It is likely that you would want your network adaptor to obtain DNS Server IP addresses

from the DHCP Server. If you look at the graphic below, this adaptor has manually specified

DNS Server IP addresses.

Figure 6: Verify DNS Server Settings

You may need to change to Obtain DNS server address automatically in order to get a new DNS server IP. To do this, open the Properties tab of your network adaptor and then

click on Internet Protocol Version 4 (TCP/IPv4).

7. Release and renew your DHCP Server IP address (and

DNS information)

Even if your adaptor is set to pull DNS information from DHCP, It is possible that you have

an IP address conflict or old DNS server information. After choosing to obtain the IP and

DNS info automatically, I like to release my IP address and renew it.

While you can do this with a Windows Diagnosis in your network configuration, I like to do

it in the command prompt. If you have UAC enabled, make sure you run the Windows cmd

prompt as administrator then do:

IPCONFIG /RELEASE

IPCONFIG /RENEW

Then, do an IPCONFIG /ALL to see what your new IP and DNS Server info looks like.

8. Check the DNS Server and restart services or reboot if

necessary

Of course, if the DNS server is really hung, or down, or incorrectly configured, you are not

going to be able to fix that at the client side. You may be able to bypass the down server

somehow, but not fix it.

Thus, it is very likely that you, or the admin responsible for the DNS server, need to check

the DNS Server status and configuration to resolve your DNS issue.

9. Reboot your small office / home DNS router

As I mentioned above in #2 and showed in Figure 3, on home and small office routers, the

DNS server settings are typically handed out via DHCP with the DNS server set to the IP of

the router and the router will proxy the DNS to the ISPs DNS server.

Just as it is possible that your local PC has network info (including DNS server IP

Addresses), it is also possible that your router has bad info. To ensure that your router has the

latest DNS server information, you may want to do a DHCP release and renew on the routers WAN interface with the ISP. Or, the easier option may be just to reboot the router to get the

latest info.

10. Contact your ISP

We all know how painful it can be to contact an ISP and try to resolve a network issue. Still,

if your PC is ultimately getting DNS resolution from your ISPs DNS servers, you may need to contact the ISP, as a last resort.

Summary

DNS resolution is a critical piece of our network infrastructure and it must work properly for

our network applications to function. In this article, I have given you 10 different ways to

troubleshoot DNS resolutions issues, hope they are useful!

System TipThis article applies to a different version of Windows than the one you are using.

Content in this article may not be relevant to you.Visit the Windows 7 Solution Center

This article was previously published under Q314095

For a Microsoft Windows 2000 and Microsoft Windows NT 4.0 version of this article, see

163391.

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On This Page

Summary

This article describes ways to diagnose and resolve issues that can cause problems when you

try to use one of the following to communicate with servers on the Internet:

Internet browser

File Transfer Protocol (FTP)

Telnet

This article assumes that you can successfully connect with and log on to your Internet

service provider (ISP).

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More information

Any one of the following issues can cause problems when you try to communicate with a

server on the Internet:

The server is not functioning correctly or has been temporarily removed from

the Internet.

Your Internet browser is not configured correctly.

The TCP/IP configuration for your dial-up connection to your ISP is incorrect.

Your ISP's Domain Name Service (DNS) server is not working correctly.

Hosts files in the System_drive:\Windows,

System_drive:\Windows\System32\Drivers, and System_drive:\Program

Files\Network Ice\Black Ice directories may be damaged or corrupted.

Note System_drive is a placeholder for the drive where Windows is installed,

To determine the cause and resolution of the problem that you are experiencing, follow the

procedures in each of the following sections, in the order that they are presented in. After you

complete a procedure, try again to see whether you can successfully communicate with

servers on the Internet.

Try a known good server

If you cannot communicate with a specific server on the Internet, try to connect to the

Microsoft Web site by using its fully qualified domain name (FQDN):

http://www.microsoft.com

An FQDN is made up of a host name (in this case, "microsoft") and a domain name (".com").

If you can connect to the Microsoft Web site by using its FQDN, the TCP/IP configuration on

your computer is correct.

If you can connect to the Microsoft Web site but you cannot connect to another specific

Internet site after several tries, the other site may not be functioning correctly or may be

temporarily removed from the Internet. Try to connect to some different Web sites. If you can

connect to some Web sites but not to other Web sites, contact your ISP if you need help.

If you cannot connect to any Web sites, there may be an issue with your Internet browser

configuration or with the TCP/IP configuration for your dial-up connection to your ISP.

Make sure that your browser configuration is correct

Make sure that your Internet browser (for example, Microsoft Internet Explorer) is correctly

configured to connect to the Internet through the dial-up connection to your ISP, and make

sure that your Internet browser is not configured to connect through a proxy server. (A proxy

server is a computer or a program that acts as a "go-between" barrier between a local area

network (LAN) and the Internet. A proxy server is a firewall component that presents one

single network address to external sites.)

To verify these settings, start Internet Explorer, and then click Internet Options on the Tools

menu. Click the Connections tab, and then view the settings that relate to your ISP.

To see whether your browser is using a proxy server, click LAN Settings.

Confirm your Internet Protocol (IP) address

If your ISP has given you a static (permanent) IP address, make sure that the TCP/IP

configuration for your ISP connection contains the correct information. Follow these steps:

1. Connect to your ISP. 2. Start a command prompt, type the following command, and then press ENTER:

ipconfig /all

The ipconfig /all command displays Windows TCP/IP settings for all your

network adapters and modem connections. The address for a modem

connection is displayed as "NDISWAN x adapter", where x is a number. The

default gateway for the NDISWAN x adapter is the same as the IP address. This

is by design. More than one NDISWAN x adapter may be displayed. Any

NDISWAN x adapters that are not currently in use display zeros for the IP

address.

3. If the IP address that is displayed for your dial-up connection to your ISP does not match the IP address that your ISP gave you, change the IP address that is

displayed so that it matches the address that your ISP gave you. Follow these

steps:

a. Click Start, point to Settings, click Control Panel, and then double-click Network Connections.

b. Right-click your Internet connection, click Properties, and then click the Networking tab.

c. Click the Internet Protocol adapter, and then click Properties. d. If the settings are not correct, change the TCP/IP settings to match the

settings provided by your ISP, click OK, and then click OK again.

Turn on the option to use a default gateway on the remote network

If you connect to a local network by using a network adapter and, at the same time, connect

to your ISP by using a modem, configure your dial-up connection so that any routing

conflicts are resolved in favor of your dial-up connection to your ISP. Follow these steps:

1. In Control Panel, double-click Network Connections. 2. Right-click your Internet connection, click Properties, and then click the

Networking tab.

3. Click the Internet Protocol adapter, click Properties, and then click Advanced. 4. Click to select the Use default gateway on remote network check box, and

then click OK.

5. Click OK.

Check the transfer and receive lights

If you connect to a local network by using a network adapter and, at the same time, connect

to your ISP by using a modem, a conflict between your network adapter and your modem can

prevent your modem from sending information to servers on the Internet. To verify that

TCP/IP packets are being routed through your modem to your ISP, follow these steps:

1. Connect to and log on to your ISP. 2. Use the ping command to cause your modem to send test information. At a

command prompt, type the following command, and then press ENTER:

ping IP address

where IP address is the IP address of a known good server on the Internet. If

you do not know the IP address of a server on the Internet, use the IP address

for ftp.microsoft.com, 207.46.133.140.

Dial-Up Networking Monitor uses lights to show the modem status.

If the transfer (Tx) light in Dial-Up Networking Monitor flashes when you ping

a server on the Internet, TCP/IP information is being routed through your

modem to your ISP.

If the transfer (Tx) light in Dial-Up Networking Monitor does not flash when

you ping a server on the Internet, packets are not being routed through your

modem. Make sure that the IP address that your ISP assigned to you for your

dial-up connection is different from the IP address for your network adapter or

loopback driver (if one is installed). Also, the IP address of your network

adapter or loopback driver must not be on the same network as the IP address

that your ISP assigned for your dial-up connection.

If the receive (Rx) light in Dial-Up Networking Monitor does not flash when

you ping a server on the Internet, packets are not being received from your ISP.

Contact your ISP if you need help.

If the receive (Rx) light in Dial-Up Networking Monitor flashes when you ping

a server on the Internet, but you still cannot connect to the server by using its

FQDN, there may be a name resolution issue.

Test the name resolution

A DNS server provides host name resolution. If you cannot connect to a server on the

Internet by using its FQDN, there might be an issue with the DNS configuration of your dial-

up connection to your ISP or with your ISP's DNS server.

To determine whether there is an issue with the DNS configuration of your dial-up

connection to your ISP, follow these steps:

1. At a command prompt, type ipconfig /all, and then press ENTER to display the IP address of your DNS server. If the IP address for your DNS server does not

appear, contact your ISP to obtain the IP address for your DNS server.

2. To verify that your computer can communicate with your DNS server, ping your DNS server's IP address. The reply looks something like this:

3. Pinging ###.###.###.### with 32 bytes of data: 4. 5. Reply from ###.###.###.###: bytes=32 time=77ms TTL=28 6. Reply from ###.###.###.###: bytes=32 time=80ms TTL=28 7. Reply from ###.###.###.###: bytes=32 time=78ms TTL=28

Reply from ###.###.###.###: bytes=32 time=79ms TTL=28

The series of number signs (###.###.###.###) represents the IP address of the

DNS server.

If you cannot successfully ping the IP address of the DNS server, contact your ISP to verify

that you are using the correct IP address and that the DNS server is working correctly.

If you can ping the IP address of your DNS server but you cannot connect to a server on the

Internet by using its FQDN, your DNS server may not be resolving host names correctly. If

more than one DNS server is available for your ISP, configure your computer to use a

different DNS server. If using another DNS server resolves the issue, contact your ISP to

correct the issue with the original DNS server.

Examine the host files

Open Internet Explorer. Connect to the Internet. Type www.microsoft.com and other FQDN

addresses in the address bar, and then click Go. MSN Search reports that no page is found.

However, if you type the IP address for any one of the Web sites, the Web site appears.

To resolve this issue, follow these steps:

1. Search for hosts files on the local hard disk(s).

2. If file name extensions are visible, find any hosts file without the .sam extension, open it with Notepad to verify that it contains references to the sites

that are unavailable.

3. Delete all hosts files that do not have the .sam extension.

When you have verified the correct IP address for your DNS server, update the TCP/IP

settings for your dial-up connection to your ISP. To change or add a valid IP address for your

DNS server for a Dial-Up Networking phonebook entry, follow these steps:

1. In Control Panel, double-click Network Connections. 2. Right-click your Internet connection, click Properties, and then click the

Networking tab.

3. Click the Internet Protocol adapter, and then click Properties. 4. Click Use the following DNS server addresses, and then type the correct IP

address in the Preferred DNS Server box.

5. Click OK, and then click OK again.