RFC 1996 / START HERE
DNS NOTIFY, before the details
DNS means Domain Name System. NOTIFY is the name of a DNS operation that alerts authoritative servers about a possible change to a zone, a managed part of the naming tree.
A configured master tells its secondary servers to check for new zone data. The secondary asks for the SOA (Start of Authority) record and compares its version number before deciding whether to transfer a copy.
Why it exists
Without notification, changed data may wait for periodic refresh checks to spread. NOTIFY prompts an earlier check while keeping the notification, SOA query and zone transfer separate.
A familiar example
A fictional picnic.example zone changes from serial 10 to 11. A NOTIFY acknowledgement confirms receipt of the hint, not that another server now has 11. The secondary still checks its configured source and fetches data if needed.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Find the servers that should hear about a changeDNS is the Domain Name System. A zone is a managed portion of its naming tree. Authoritative servers serve that zone’s records; a resource record, or RR, is one piece of DNS data.→
- Read the NOTIFY request and acknowledgementNOTIFY reuses the DNS message envelope with opcode 4. The question names the zone and asks about its SOA record; it does not carry an entire zone.→
- Check the notifying master before transferring a zoneA notification prompts a normal SOA query. The secondary compares that answer’s zone serial number with its local copy before deciding whether it needs a transfer.→
- Treat optional Answer data as an untrusted hintA NOTIFY request may include an Answer RRset, a set of resource records. That section can save a check only in one narrow case; it cannot replace the normal update process.→
- Bound retries and distinguish completion from successNOTIFY uses UDP by default. Because packets can be lost, the sender keeps per-destination notification state and retries within configured limits.→
- Pace notifications and propagate only after checkingA zone’s authoritative servers can receive duplicate events and notify their own peers. Coordination prevents notifications from multiplying expensive simultaneous work.→
This introduction explains RFC 1996 (1996). Read the original RFC ↗