DNS client
DNS client- a program (or a module in the program) that determines the host address by its full name (the dot at the end is usually either added by the DNS client or implicitly implied, however, in the case of using domain suffixes, there may be differences in the behavior of the client when determining the name with a dot at the end and without).
DNS server operating modes
The DNS server that performs the client's request can operate in one of three modes:
- the mode of forwarding (transferring) requests to another DNS server - in this case, the request is almost the same as the request of the DNS client. (This scheme is used when using caching DNS servers and servers in the DMZ).
- mode of self-execution of a recursive query.
- zone maintenance mode (in this case requests for extraneous (non-authoritative) zones are not accepted, addresses of root servers are returned instead).
IN general case configuration is possible when different servers and zones, the DNS server behaves differently (for example, from local network accepts recursive requests, from external - only requests for authoritative zones, or forwards requests to another server only for specified zones).
Workstations and servers in Active Directory use many DNS SRV records to locate the nearest domain controller in a site and to dynamically update the workstation DNS record.
Interface between the program and the DNS client
Most programs that use DNS functions do not implement its functionality on their own (through sockets), but use either the DNS client functions provided by the operating system or use a ready-made client library. The minority are mainly low-level utilities and server software that requires more specific functionality than is provided by the DNS client.
see also
Notes
Literature
- Paul Albitz and Cricket Lee - DNS and BIND, ISBN 5-93286-035-9, Symbol-Plus, 2002
Links
Wikimedia Foundation. 2010 .
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All webmasters and many ordinary users, who vaguely represent the mechanisms of the sites, know well what site hosting is. But not all network users know what DNS is, why it is needed and why it is impossible to do without it. So what is it and what is it eaten with? DNS is an abbreviation of the English definition of Domain Name System - domain name system. DNS is distributed system, which can, upon request for a specific domain name, report the IP address of the device. The name IP address is also derived from the English phrase Internet Protocol Address, which refers to the unique identifier or address of a device on a network, whether it is a local network or The World Wide Web. The devices are mostly users' computers, but there may be other devices, including printers, etc.
As you know, each computer on the network has its own unique IP address, which is necessary for networking. Without knowing this address, no user will be able to send a request or access this device. A webmaster, creating his site and choosing hosting for wordpress, hosting for joomla or hosting for other CMS, receives the IP address of his resource. An IP address consists of a 4-byte number, which is separated by dots and looks something like this: 183.76.34.23, 162.34.12.183, etc. Of course, not everyone will be able to remember this set of numbers, and if they remember, then only a few sites, which is not enough for normal operation online. This is where DNS helps, which serves to determine the IP address by a domain name, which is much easier to remember and find.
Determining an IP address by a domain name is also called resolving. To provide quick search the desired site or resource, a whole hierarchical system of DNS servers was developed. All web developers who use web hosting know that a domain name can consist of several parts ( domain names 1, 2, 3 levels). A certain group of servers is responsible for each part of the domain name, so each user request is sent to several servers, after which it reaches desired server, which hosts the desired site.
To clearly demonstrate hierarchical work DNS systems, imagine how the primer.narod.ru site will be searched. First, a request is made to the DNS server that is responsible for the ru zone. Further, requests are sent to the server that is already responsible for the narod.ru zone. After that, the computer receives the address of the server responsible for the primer.narod.ru zone, and this server already indicates which address corresponds to the site primer.narod.ru and the user gets to the desired resource. Regardless of whether the web developer uses a free or paid hosting, all requests to its resource will follow a similar pattern.
The DNS server is a specialized software required for DNS service. The DNS server can operate in forwarding mode (transmitting a request to another server), in zone maintenance mode (only requests from the serviced zone are served, while requests for other zones are not accepted), in the mode of independently executing a recursive query. The DNS client is separate program or a module in a program that is used to determine the address of a node from its name. Usually, the DNS client function is built into the browser used by the user to surf the web, so he may not even know what is happening "there" when entering and searching for a particular site.
DNS client- a program (or a module in the program) that provides the determination of the node address by its full name(the dot at the end is usually either added by the DNS client or implicitly implied, however, in the case of using domain suffixes, there may be differences in the behavior of the client when determining a name with and without a dot at the end).
The DNS client function is built into almost any program designed to work in Internet networks. However, most DNS clients do not know how to perform recursion themselves, because otherwise their algorithms would have to be unnecessarily complicated. In addition, the use of recursion by DNS clients would not allow access restriction regimes during external network and DNS caching.
Specialized programs
DNS diagnostics are used specialized programs- nslookup and dig. The Windows version of nslookup (like many windows DNS clients) supports WINS, which can be confusing if WINS and DNS servers respond differently. Some versions of nslookup on Unix support yp (NIS) in addition to DNS, which also makes diagnostics more difficult. When checking integrated with Active Directory DNS servers can use the dcdiag utility.DNS server operating modes
The DNS server that performs a client request can operate in one of three modes:* mode of forwarding (transferring) requests to another DNS server - in this case, the request is almost the same as the request of the DNS client. (This scheme is used when using caching DNS servers and servers in the DMZ).
* mode of self-execution of recursive query.
* zone maintenance mode (in this case, requests for extraneous (non-authoritative) zones are not accepted, addresses of root servers are returned instead).
In many versions of BIND, queries to other DNS servers came from port 53 (the port on which DNS queries, both TCP and UDP), as opposed to client applications, using an arbitrary sender port (from an unregistered range).
Working with DNS of various programs
The mail server uses a DNS client to query MX, SPF, A-records (for example, sendmail uses MX-records in ascending order of priority, but in the absence of a suitable route, as last try uses an A record), PTR records (to determine the hostname). In addition, many versions mail servers use names retrieved via a PTR record query to determine if a given name has an MX record, this is used to automatic failure in delivery at non-mail servers(mostly botnets).In the general case, a configuration is possible when the DNS server behaves differently for different servers and zones (for example, it accepts recursive requests from the local network, only requests for authoritative zones from the external network, or forwards requests to another server only for specified zones).
Workstations and servers in Active Directory use multiple DNS SRV records to determine the location of the nearest domain controller in a site and to dynamically update the DNS record about workstation.
Interface between the program and the DNS client
Most programs that use DNS functions do not implement its functionality on their own (through sockets), but use either the DNS client functions provided by the operating system or use a ready-made client library. The minority are mostly low-level utilities and server software that needs more specific functionality than is provided by the DNS client.If clients encounter an inability to access resources on the network using a hostname or a fully qualified domain name, the cause of this issue is usually related to one of these errors:
- Negative response stored in local name resolution cache
- The DHCP server provided the clients with an incorrect name resolution server address
- Incorrect static TCP/IP protocol parameters specified
- Other domain names are not specified as suffixes, added in DNS suffix order ( Extra options TCP/IP protocol)
- Network hardware error (network adapters, cables, switches, routers, etc.)
If clients cannot access the system using a fully qualified domain name, it is worth first determining whether the problem is with the name resolution service or with the network itself. by the most in a simple way to do this is to send a test echo packet to the remote system with an IP address. If remote system successfully responds to the test echo packet, then the problem is indeed with the name resolution service (if it is not, check for problems in hardware network environment).
You can then try to send a test echo packet using the fully qualified domain name.
If ping command will display wrong address IP, you need to find the source of the incorrect IP address. Most likely, the source of the invalid IP address is the DNS server or the Hosts file on the client computer (located in the %systemroot%\system32\drivers\etc directory). If in hosts file static entries are not specified, you can try to find the source of the incorrect conversion using the nslookup utility.
Now let's assume that the correct IP address is shown when using a fully qualified domain name. After that, you need to send a test echo packet, specifying only the name of the remote host. If the test echo packet fails, then the source of the problem can be considered found, because DNS suffixes are not added to name resolution requests. This problem is solved by adding DNS suffixes to the appropriate suffix list. This list is available on the DNS tab in the TCP/IP protocol properties window for a particular network interface.
Common DNS Client Issues
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Possible reason |
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After changing the host record on the DNS server, clients are unable to access this host |
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The user receives the message "Network path not found" ("Network Path not found") when trying to access a network share |
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Client receives incorrect response from DNS server |
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Names and IP addresses of client nodes are not dynamically registered on the primary DNS server |
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Customer experience problems are usually small in scope and use correct technique can be quickly corrected. On the other hand, server problems sometimes require some time to isolate the source of the problem.
Sometimes it becomes very annoying that you cannot use the Internet due to a completely banal error " dns server doesn't answer." In the vast majority of cases, when it is not possible to find the dns address of the server, the problem can be solved in a matter of minutes. In this article, we will consider in detail all the ways to solve this problem.
DNS server is a utility that redirects a Web user to a website. The fact is that any Internet page is stored on a server that has its own IP address. To grant a user access to a site, a DNS server connects the user's computer to the server. In other words, the DNS server is the link between the user and the site.
Errors "dns server not responding" or "cannot find dns address"
Often the browser complains that it cannot find the dns address of the server. This message occurs most often among desktop users using a cableless connection (3G/LTE modem or wifi router). However, it can also appear in those who use wired Internet. This error means that the aggregate from which the user accesses the site cannot find a DNS address that will redirect him to the server with the page in question.
What to do if the dns server is not responding or unavailable
Before trying to decide this problem, you must first find out why it arose:
- Because of wrong settings modem or router;
- Due to incorrect settings of the operating system (the site is blocked by a virus or firewall, or the Windows DNS client has failed);
- Due to an outdated driver network card.
To do this, go to the network control panel located in the lower right corner of the task bar. It has a monitor icon with an Enternet cable next to it. Click on it with the left mouse button. Next click right key manipulator on the field where it says "Connected", then go to "Properties". We click on the “Network” tab and go to the “Properties” item, after clicking on “Internet Protocol version four”. In the tab with DNS addresses, try selecting the option "Load DNS server on the machine." If this does not help, then enter the address (preferred and alternative) yourself. It is written in contractual connection certificates. The DNS address can also be obtained from the provider by calling him.
Advice: the correct DNS address can be registered not only in Windows settings, but also in the control panel of the router itself. If you are using software utilities from TP-LINK, then use the parameter quick setup(Quick setup).
Often a virus, carelessly uploaded by a user, blocks access to other sites. To check the system for existing malware, you should scan it with an antivirus. At the same time, it is better to scan with a program that does not require installation on the desktop and is located on a Live-CD or Live-flash drive (Live media are storages that are independent of the main system). For such purposes, we can recommend Dr. Web CureIt! Portable anti-malware is good because, being placed on a Live-CD or Live-flash drive, it cannot be infected with viruses.
Firewall settings
There is a possibility that access to the site is blocked native Windows Farewall or a firewall (another name for a firewall) that comes with your antivirus. The firewall blocks access to sites that it considers malicious. If you know that the blocked page is really safe, then you can disable the firewall for a while or reset its settings to the initial ones (then the list of blocked pages will be reset). How to turn off the Microsoft firewall? Click Control Panel->Windows and Security-> Windows Firewall. In the left panel there will be an item "Enabling and shutdown Windows Firewall". Click it, then move all the toggle switches to "Turn off Windows Firewall". Save these settings.
Advice: windows firewall- key. Turning it off will disable other firewalls.
Update network card drivers
Often the desktop refuses to go online due to outdated drivers network card. To check their status, use Driver utility booster. This application will help you find not only drivers for network controllers and install them, but also update the functionality of other components.
Advice: you can update the driver network board And standard utilities Windows. Go to "Devices and Printers", then double-click the left mouse button on your desktop icon. In the "Hardware" tab, look for accessories marked as " Network adapters and navigate to their Properties. There, click on "Driver" and select "Update".
This method consists in resetting the desktop and router settings. The sequence of actions is as follows: you need to disconnect the router from the 220V network and leave it unconnected for 5 minutes. Next, you need to restart the computer and connect the router back to the outlet.
Advice: before turning off the router, you should go to its settings menu and reset the default settings.
This problem can be fixed in two ways. The first - the least painful - to register the DNS address not through the Panel Windows controls, but through the menu of the router. The second is to perform a system restore. Go to the Control Panel, then - "System and Security" - "Restore a previously saved desktop state." In a few minutes, when the utility collects all the registered backup points, you need to select one of them. Near each point the date of its creation is registered. Select the one when the DNS client functioned normally and confirm the system reset.
How to find dns server address
The correct DNS address is specified in the contract for connecting the desktop to the Web. It is compiled by the provider, so the possibility of error is excluded. If there is no access to the certificate, then you can call the provider or contact him through technical service support and ask them again to provide the exact DNS address.
Where can I set the dns server address in Windows
It can be configured through Windows utilities (path: network icon in the taskbar - "Settings" - "Network" - "Internet Protocol v4" - "Properties" - tab with DNS addresses) or through the control panel of your router or modem.
Programs for setting up a DNS server
If the dns server is unavailable, then the utility DNS Jumper will help fix this problem. Its advantage is that it is portable and does not require installation. In the "Select DNS Server" tab, you can select the DNS address manually or leave the choice to the utility itself. In this case, DNS Jumper will choose the most stable and fast server on the this moment, while the error "dns server is not responding windows" will be removed. You can also download the DOT VPN add-on to your browser. This extension allows you to choose not only the address, but also the country from which the user will enter. That is, you can physically be in Germany, but go to the site as a resident of the Netherlands. Very useful extension, since some pages are blocked by state governments, and DOT VPN allows you to bypass this ban. Similar functionality has VPN setup" in Opera browser. It turns on like this: Settings-> Security-> VPN (switch the toggle switch to "Enable" and select the "Optimal location" item).
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