Domain Name System (DNS) FAQ

Why do I need to register DNS servers for the blocks assigned to my organization?

DNS delegation for IP address blocks allows reverse resolution: finding out the name associated with an IP address that is being used by a computer.

How can I enter or modify the DNS servers to provide reverse resolution for an IP address block?

In addition to managing Internet number resources for Latin America and the Caribbean, LACNIC is also responsible for global reverse resolution. To delegate a block’s reverse resolution, go to and login with the user ID of your organization's administrative contact. Once you have logged in, go to the IP/ASN section located to the left of the menu and identify the IPv4 or IPv6 block you wish to delegate. Note that you must identify the parent block of the assigned block that you wish to delegate. If you would like to delegate the entire block, for example 201.219.252/22, click on Delegate (rDNS). The system will show the ranges available for delegation. On the following screen you must specify the range you would like to delegate and enter the servers responsible for the block’s reverse DNS resolution. Keep in mind that each Class C that makes up this /22, in this case the four /24s, must be properly configured on your server.

If you would like to delegate a smaller block, for example the first /24 corresponding to this /22, you will have to complete the same process. However, on the screen prior to entering the name of the servers you must specify the /24 range that you want to delegate.

To modify reverse resolution servers that have already been delegated, click the Edit button in the Delegate (rDNS) section and change the name of the servers. Note that you must enter the host names of the servers, not their IP addresses.

See detailed instructions on this topic at the following link:

What do the Lame Delegation messages I receive mean?

A Lame Delegation means that a DNS delegation has problems. This happens when the information on the IP address block in the DNS server registered in the database is not accurate, or when the DNS server cannot be accessed by LACNIC's monitoring system and so causes reverse resolution errors. In such cases you should check your DNS server configuration.

How can I check the status of the DNS servers responsible for reverse resolution?

LACNIC's Whois server indicates the status of the IP address blocks' DNS delegation, as well as which servers are configured to respond to that assignment.

This information is available in the Nserver, Nsstat and Nslastaa fields of the responses provided by the Whois server when making a query by IP address block.

The Nserver field specifies which DNS server must respond to the delegation, the Nsstat field specifies the delegation's status and the Nslastaa field specifies the last date on which a correct configuration was observed on this server. To verify that your server is responding with the right information you can perform a test using the Dig application. You should receive a Noerror response if all is well. Nxdomain or Servfail responses mean that there is a configuration error in your DNS server.




Why do I get a system error when trying to register my DNS servers?

This can occur when the DNS servers specified in the system are not yet properly configured for the reverse resolution of an IP address block.

The DNS server must have information on every network that makes up the IP address block. For example, in the case of a /20 the server must have information on the 16/24 networks it contains. To check your DNS, follow the recommendations specified in the previous question.