Reverse DNS Resolution 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, in other words, finding out the name associated with an IP address used by a specific device.

How do I enter or modify the DNS servers to provide reverse resolution for a block of IP addresses?

In addition to managing Internet number resources for Latin America and the Caribbean, LACNIC is also responsible for reverse resolution at the global level. To delegate a block's reverse resolution, go to and log in with the user ID of your organization's administrative contact.

Once you've logged in, go to the “IP/ASN” section located to the left of the menu and identify the IPv4 or IPv6 address block you wish to delegate. Note that you must select its parent block. If you want to delegate the entire block, in this case 201.219.252/22, click on “Delegate (rDNS).” The system will display the ranges available for delegation. On the next screen, must specify the range you want 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 want to delegate a smaller block, for example, the first /24 corresponding to this /22, you will have to complete the same process. However, before entering the name of the servers, you must specify the /24 range you wish to delegate.

To change the names of reverse resolution servers that have already been delegated, go to “Delegate (rDNS)” and click on the “Edit” icon. Keep in mind that you must enter the host names of the servers, not their IP addresses.

A detailed guide on this topic is available at

What is the meaning of the Lame Delegation messages I receive?

A “lame delegation” message appears when there is a problem with a DNS delegation. This happens when the information in the DNS server registered in the database for the IP address block is not accurate, or when the DNS server cannot be accessed by LACNIC's monitoring system, thus generating reverse resolution errors. In such cases, you should check your DNS server configuration.

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

The LACNIC Whois server reports the status of an IP address blocks' DNS delegation, as well as the serversthat 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 an IP address block is queried.

The “nserver” field specifies the DNS server that 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. If everything is OK, you should receive a NOERROR response. NXDOMAIN or SERVFAIL responses mean that there is a configuration error in your DNS server.

dig soa @nserver

dig soa @NS.LACNIC.NET

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Why does a system error show up when I try to register my DNS servers?

This can happen 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.