Servers as a software component of a computing system provide a client with access to certain services or resources. Sometimes this access is missing. There may be several reasons.
The most commonplace reason is the lack of a network connection due to a malfunction of the cable or network cards. Check if everything is in order.
If everything is in order with this, you need to check if the IP address is included in the list of allowed ones, since information about it is needed to connect to the node.
The server may be configured for limited service and the IP address that was used to check the server responses was not included in this list. After repeating the check, specify a different IP address included in the limited list of server interfaces. If there is a response from this address, then add the missing IP address.
The server might not respond if auto-generated reverse lookup zones are disabled (by default, servers automatically create three standard reverse lookup zones). These zones are created from regular IP addresses that are not used in reverse lookup. Disabling them requires manual configuration.
In addition, the server may provide incorrect data when responding to a request. Here are the probable reasons:
- there may have been an error while manually adding or modifying resource records in the zone;
- resource records were not updated, and obsolete records that became unnecessary were not deleted.
It happens, albeit rarely, that the server uses a non-standard configuration and is configured to block traffic through known ports in use.
In advanced security or firewall settings, add a packet filter to these settings to allow traffic to standard ports.
In conclusion, it should be noted that many problems begin precisely with unsuccessful requests from the client, so often the reason should be sought in this. Due to a failed recursive request, the server cannot resolve names for which it is not authoritative.
Servers on the path of the recursive request only respond to correct data and forward it further.
If a recursive request expires before the request can complete, or if the server provided invalid data, the request may also fail.
