Bound retries and distinguish completion from success
05NOTIFY uses UDP by default. Because packets can be lost, the sender keeps per-destination notification state and retries within configured limits.
If TCP is needed, for example by a firewall policy, send the request once. A stalled NOTIFY transaction must not stop either server answering ordinary DNS requests. Its reasonable timeout is an operational choice, not a new fixed protocol deadline.
Source for this drawing: RFC 1996 · Read RFC source: § 3.4 and related clauses ↗
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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.
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Use UDP unless there is reason to use TCP. A UDP response must match the query ID, QNAME, source IP address and source port before it ends this retry event.
- Use UDP unless there is reason to use TCP. A UDP response must match the query ID, QNAME, source IP address and source port before it ends this retry event.
- UDP stops after a matching response, too many copies or a port-unreachable indication. Retry interval and retry limits should be administrator parameters; 60 seconds and five retransmissions are suggested defaults, not universal mandatory values.
- TCP sends the NOTIFY request once and times out after a reasonable interval; both servers must continue ordinary name service while it stalls. A NOTIMP response should complete the notification transaction for that receiver, not certify refreshed data.
Fictional picnic.example zone and documentation-only addresses. Drawings are schematic; no DNS traffic, server configuration or zone transfer is performed.
Read the RFC section ↗