Policy Manual (v2.2 – 06/10/2014 )

5. Delegation of Reverse Resolution

5.1. Introduction

Most connections through the Internet use machine names instead of IP addresses. Names are obviously easier to remember than numbers. However, Internet connections between computers connected to this network are made using IP addresses. Therefore, before a connection can be made, the computer's name must be translated into its IP address. This process is known as direct DNS Resolution, i.e., converting names into IP addresses.
it is frequently also necessary to perform the reverse operation, known as Reverse Resolution.
This conversion attempts to find the name associated to an IP address.
Reverse resolution is only possible with the use of a pseudo-domain, "in.addr-arpa", an acronym for "Address and Routing Parameter Area."
DNS delegation of this pseudo-domain is responsibility of Internet Registries, as they are responsible for allocating IP addresses.

5.2. DNS Server Registration

All allocated IP address space must have an associated DNS server, which shall be responsible for reverse resolution. In the case of LACNIC's area of coverage [Annex 1], these servers must be registered at LACNIC, which in turn is responsible for the reverse resolution of blocks administered by this organization.
LACNIC may use information obtained through reverse resolution as an indicator of the utilization of allocated IP address blocks.
DNS server registration of the IP address space administered by LACNIC shall vary according to the size of the allocated space.
Blocks allocated by LACNIC with prefixes shorter than or equal to /16 shall have their DNS servers responsible for reverse resolution registered at LACNIC. Information shall be entered in relation to /16 blocks. Suballocations of segments with longer prefixes within these blocks shall have their DNS servers registered at the organizations that received the blocks with prefixes shorter than or equal to /16 directly from LACNIC.

Blocks allocated by LACNIC with prefixes longer than /16 shall register at LACNIC the DNS servers responsible for the reverse resolution of all blocks with the prefix /24 that account for the total IP address space allocated by LACNIC. Thus, suballocations with prefixes of up to /24 made within these blocks must have their DNS servers registered at LACNIC.

For example:

  • ISP-A receives from LACNIC a /15 prefix (200.0.0.0/15). It must report to LACNIC which DNS servers will be responsible for the reverse resolution of each one of the /16 prefixes that make up the allocated block, i.e., blocks 200.0.0.0/16 and 200.1.0.0/16. The DNS servers of suballocations of longer prefixes made within this block must be registered at the DNS servers of ISP-A, which in turn are registered at LACNIC's DNS servers as responsible for the reverse resolution of blocks 200.0.0.0/16 and 200.1.0.0/16.
  • ISP-B receives from LACNIC a /20 prefix (200.2.0.0/20). It must report to LACNIC which DNS servers will be responsible for the reverse resolution of blocks 200.2.0.0 to 200.2.15.0.
    If ISP-B suballocates a block with a prefix longer than /21 and shorter than or equal to /24, it must register at LACNIC's servers the new DNS servers responsible for the reverse resolution of the suballocated block.
    Thus, within LACNIC's IP address administration system, it shall not be possible to register DNS servers for suballocations made in blocks with prefixes shorter than or equal to /16 that have been directly allocated by LACNIC. The organization receiving the allocation shall maintain the registry of the DNS servers responsible for the reverse resolution of suballocations made within that block.
    This shall also be reflected on the WHOIS server database. In other words, in the case of suballocations within blocks with prefixes shorter than or equal to /16 directly allocated by LACNIC, the DNS servers responsible for the reverse resolution of those suballocations shall not be visible through WHOIS. This is because these servers are not registered at LACNIC.
    Should it be necessary to identify the DNS servers of suballocations made within these blocks, the use of DNS query tools is recommended.
    This condition does not exist for allocations with prefixes longer than /16 made by LACNIC. In this case, suballocations of prefixes of up to /24 made within blocks allocated by LACNIC and having prefixes longer than /16 may have a DNS server delegated through LACNIC's IP address administration system.
    LACNIC's IP address administration system does not accept the delegation of DNS servers for blocks with prefixes longer than /24. For these cases the adoption of BCP 20 is recommended.

To summarize:

Prefix of the block allocated by LACNIC - DNS server for suballocations made by LACNIC must be registered at:

  • /16 or shorter: ISP that received the block.
  • /17 or longer: LACNIC.