Reverse DNS Resolution

LACNIC's DNS servers are responsible for the reverse resolution of the IP addresses assigned to Internet Service Providers (ISPs) and other organizations in the region.

Currently, this function is performed by six servers located not only in Latin America and the Caribbean, but also in Africa, North America, Asia, and Europe.

LACNIC is not responsible for the reverse resolution of domain names.

Reverse resolution delegation is registered on MiLACNIC

DNS servers are updated daily based on system records at the following times:

LACNIC recommends configuring reverse resolution for the IP address blocks for which your organization is responsible. Special domain names have been created for reverse resolution: in-addr.arpa for IPv4 blocks and ip6.arpa for IPv6 blocks.

To include an IP address in the DNS name hierarchy, a name must be created that will represent the address within this structure.

Under the DNS name hierarchy, the leftmost portions of a domain name are the most specific, while the rightmost portions are the least specific. In the case of IP addresses, however, the opposite is true: the most specific portions of an address are located to the right.

This requires reversing each part of the IP address and then adding the domain name reserved for reverse resolution (in-addr.arpa or ip6.arpa).

For example, let's consider the following IP address: 10.0.0.1. To convert this address to the required format, reverse each byte (1 byte equals 8 bits) and then add the reverse resolution domain at the end: 1.0.0.10.in-addr.arpa.

Note that reverse DNS delegation of IPv4 addresses must respect the byte boundaries for each part of the address. In other words, it is possible to perform reverse DNS lookups on the first byte, which represents a /8 block; on the second byte, which represents a /16 block; or on the third byte, which represents a /24 block.

This is why only /24 or /16 block delegations can be registered in LACNIC's DNS servers. Organizations receiving IP address blocks with prefixes from a /24 to a /17 can perform the DNS delegation of each /24 block contained in the block they were assigned, directly on LACNIC's server.

Likewise, an organization receiving blocks with a /16 or shorter prefix may only delegate the /16 blocks contained in their assigned prefix.

The /24 blocks contained in each /16 must be delegated in the organization's own DNS server.

A similar restriction applies in the case of IPv6 addresses. Each 4-bit data nibble (representing half of a data byte) of an IPv6 address may be delegated. Example: Supposing that a /32 is received, this address range may only be delegated in its entirety. If a /33 is received, the entire /33 or longer prefixes up to a /36 contained within the /33 may be delegated.