Make room below an octet boundary
01Reverse DNS asks for a name associated with an IP address. A /26 IPv4 block contains 64 addresses, but the dotted reverse-name tree does not automatically create a boundary for those six host bits.
Add a chosen child label such as 128-26 under the parent. A delegation at that new DNS name can give organization B control of a separate zone; aliases will connect ordinary reverse queries to it.
Source for this drawing: RFC 2317 · Read RFC section 3 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
PTR means pointer: a DNS resource record used here to map an address-derived name to a domain name. It does not assign or route an IP address.
- PTR means pointer: a DNS resource record used here to map an address-derived name to a domain name. It does not assign or route an IP address.
- The fictional 192.0.2.128/26 block spans 192.0.2.128 through 192.0.2.191. The ordinary reverse owner for 192.0.2.129 is 129.2.0.192.in-addr.arpa.
- RFC 2317 adds names and delegations below the parent reverse zone. It uses existing DNS lookup behavior, rather than a new CIDR-aware resolver algorithm.
Fictional documentation addresses and .example names. Zone snippets omit TTLs, SOA timers and other deployment settings. This is DNS delegation, not a routing change or proof of identity.
Read the RFC section ↗