10 tips to help you fix a DNS failure

Source: Internet
Author: User
Tags nslookup nslookup command fully qualified domain name dns poisoning

DNS is one of the network infrastructure protocols, presumably everyone should have some understanding. DNS is one of the most important services for all windows-based networks. In the absence of DNS support, the Active Directory does not work, and it uses more features than any other type of network. As a result, it is a critical task to resolve the problem as soon as possible when there are problems with DNS. Fortunately, this process is easier in general. In this article, the author lists 10 troubleshooting techniques for DNS.

Repair DNS Failure 1: Verify network connectivity

when you find a problem with the DNS service, the first thing you should do is verify the network connectivity of the DNS server. After all, if the real problem is simply a network card malfunction, a lot of the time spent in a thorough overhaul of the equipment from the beginning can be saved.

The easiest way to
the connection situation is to log on to the DNS server and use the ping command to check the connection status with other machines. What you should do is try to ping the DNS server with a random machine. It is important to keep in mind that the ping command works only if the Internet Message Control Protocol (ICMP) packet is allowed in the configuration of the firewall.

Repair DNS Failure 2: Determine the scope of the problem

in determining the normal connection, the next step is to determine the scope of the problem. Does the Internet Name resolution service fail, or does the local name resolution service fail? For different issues, the solution to the problem is also a big difference. For example, if the local name resolution service is normal and the Internet name resolution service fails, the problem may be on the Internet service provider's DNS server.

Repair DNS Failure 3: Verify that all users are affected

the next thing to consider is whether all users on the network are affected or are limited to only a subset of the users. If you are sure that only a subset of the users are affected, check the location of the network segments where they are located to confirm that they are in the same scope. If the answer is OK, the problem may be related to a router failure or a Dynamic Host Configuration Protocol (DHCP) configuration error.

To fix DNS failure 4: Verify that the load balancing processing technology is running on the DNS server

in some cases, the company's high demand for network server resources causes the DNS servers to be dispersed across multiple identical network servers to use DNS round robin technology to implement workload load balancing techniques. A typical problem with this technique is that the DNS server does not understand that the actual situation has changed when one of the servers is down. Therefore, although one of the servers is already offline, the input traffic is evenly distributed to all the servers in the loop. The result is that load-balancing resources are having problems with intermittent connectivity.

Repair DNS failure 5: Check DNS server forwarders

If you have confirmed that the local name resolution service is functioning correctly, but the Internet Name resolution service is not working, the next thing to check is whether the DNS server is using forwarders. Although many DNS servers use root hints to provide Internet name resolution services, there are also DNS servers that use forwarders to connect to Internet service providers. If there is a problem with the Internet Service provider's DNS server, the Internet Name resolution service will fail if the entry expires in the parser cache. If you are sure that the DNS server is not using forwarders, you can also try pinging the server to see if it is online. What you might need to do is call your Internet service provider to find out if there are any DNS problems, and make sure that the network IP address used in forwarders is still valid.

Repair DNS Failure 6: Try to ping the test with a single host

If there is a problem with the name resolution service on your local network, you should choose to try to ping other servers on your network. First, you can use the network IP address of the server to ping test. In this way, you can verify that the server is still connected. Next, the computer name and the server's fully qualified domain name are used to ping the test.

If the network IP address can be pinging, but the domain name cannot be passed, the DNS server should be checked to ensure the presence of host (A) records. If a host (A) record is not available, the DNS server will not be able to resolve the host's name.

Repair DNS Failure 7: Use nslookup query domain name command

for troubleshooting DNS failures, one of the most convenient tools is the nslookup query domain name command. It can be used in a Windows command Prompt window. Windows can return the network IP address and resolution name of the DNS server (although, in general, the DNS server name appears to be unknown) as long as the input nslookup plus the host name that requires the test name resolution service. It can also provide a fully qualified domain name and network IP address for the specified host.

for two things, the nslookup command is very useful. First, it allows you to verify that the name resolution service is normal. Second, if the name resolution service does not work correctly, it can help confirm which server is being used. It is important to keep in mind that only the DNS server to which it was originally connected is listed in Nslookup's query results. These servers are not listed if name resolution requests are forwarded to other DNS servers.

Repair DNS Failure 8: Try to use an alternate DNS server

Most companies have at least two DNS servers. If there is a problem with your primary DNS server, try using an alternate DNS server. If the name resolution service works correctly after you switch the DNS server, you can confirm that the problem is really about the DNS server, not some external factors.

Repair DNS Failure 9: Scan for viruses

about a week ago, someone turned to me for help. The problem with their network is that every time an attempt is made to access a particular Web site, it is redirected to a malicious site. My first suspicion was of a DNS poisoning attack, but this possibility was excluded when it was found that only one computer was affected.

Finally, I found the problem is that a virus occupies the TCP/IP protocol stack and intercepts all name resolution requests. Although the problem appears to be a DNS problem at first, the virus actually has to bear the ultimate responsibility.

Repair DNS Failure 10: Restart the DNS server

I know this kind of measure looks like a cliché, but when all the solutions don't work out, choosing to restart the DNS server is a way out. During all these years of work experience, I have seen multiple failed name resolution services for unknown reasons, but everything is normal after restarting the DNS server.

Similarly, I have encountered at least two consumer-level routers that have stopped forwarding DNS requests while other types of traffic are still normal. In one of these cases, restarting the router solves the problem. In another case, the router must be replaced. It was analyzed that the router may have been damaged in a power outage that occurred the day before.

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