NOTIFY for DNSSEC updates

Introduction defines the NOTIFY opcode for DNS and its use to alert secondary name servers that the contents of a zone has changed. specifies the method to pass DNSSEC key changes from child to parent zones using CDS and CDNSKEY records. describes a method to pass initial DNSSEC key records from child to parent using CDS and CDNSKEY records, while describes a more secure alternative. All three of these methods currently depend on a parent zone periodically scanning child zones to check for updates, which limits the speed of DNSSEC updates and potentially puts a large load on parent zones with many child zones. A new usage of DNS NOTIFY allows a child zone to tell the parent zone that DNSSEC key information has changed, so the parent can promptly scan the child zone and perform updates. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

NOTIFY usage for key updates In , the server sending the NOTIFY queries is called the Master and the one receiving and answering them is called the Slave. In this application, a server for a child zone sends the queries, and a server for the parent zone receives and answers them. The format of a NOTIFY query and answer is unchanged from that in . The QTYPE of the request MUST be CDS or CDNSKEY, to indicate that CDS or CDNSKEY records in the child zone have been added or updated. The answer section SHOULD contain copies of the new CDS or CDNSKEY records, which the parent can use to disregard duplicate requests, as in . When the parent receives a non-duplicate request, if it already has DNSSEC key records for the child zone, it scans for updates as in . If it does not, it uses the process from or to possibly install new key records. A parent MUST ignore DNSSEC NOTIFY messages that are not for zones that are immediate children of the parent, other than optionally logging an error message. In some cases a zone may have multiple signers. The multiple signers have to coordinate CDS and CDNSKEY updates as described in and it is up to them to coordinate which of them sends NOTIFY queries, or whether they both can do so.

Identifying the parent to notify In some cases, NOTIFY messages are sent to one of the DNS servers for the parent zone, but in other cases they may be sent to a different host that manages the parent zone, analogous to Stealth servers in . This specification does not describe how to select or find the correct target of the NOTIFY.

Security considerations The NOTIFY messages are only a hint to do a scan that the parent would eventually have done anyway, so they introduce no new DNSSEC security issues. Large numbers of NOTIFY messages could cause a denial of service attack, just like any other unwanted traffic. Child servers MUST limit the number of NOTIFY queries they send and parents MUST limit the number of answers they send to avoid direct or reflection DoS attacks.