]> The Swedish Internet Foundation

Sweden johan.stenstam@internetstiftelsen.se

Internet DNSOP Working Group Internet-Draft Delegation information (i.e. the NS RRset, possible glue, possible DS records) should always be kept in sync between child zone and parent zone. However, in practice that is not always the case. When the delegation information is not in sync the child zone is usually working fine, but without the amount of redundancy that the zone owner likely expects to have. Hence, should any further problems ensue it could have catastropic consequences. The DNS name space has lived with this problem for decades and it never goes away. Or, rather, it will never go away until a fully automated mechanism for how to keep the information in sync automatically is deployed. This document proposes such a mechanism. TO BE REMOVED: This document is being collaborated on in Github at: https://github.com/johanix/draft-johani-dnsop-delegation-mgmt-via-ddns. The most recent working version of the document, open issues, etc, should all be available there. The author (gratefully) accept pull requests.

Introduction For DNSSEC signed child zones with TLD registries as parents there is an emerging trend towards running so-called "CDS scanners" and "CSYNC scanners" by the parent. These scanners detect publication of CDS records (the child signalling a desire for an update to the DS RRset in the parent) and/or a CSYNC record (the child signalling a desire for an update to the NS RRset or, possibly, in-bailiwick glue in the parent. The scanners have a number of drawbacks, including being inefficient and slow. They are only applicable to DNSSEC-signed child zones and they add significant complexity to the parent operations. But given that, they do work. Generalized DNS Notifications (see draft-ietf-dnsop-generalized-notify-00) propose a method to alleviate the inefficiency and slowness of scanners. But the DNSSEC requirement and the complexity remain. This document proposes an alternative mechanism to automate the updating of delegation information in the parent zone for a child zone based on DNS Dynamic Updates secured with SIG(0) signatures. This alternative mechanism shares the property of being efficient and provide rapid convergence (similar to generalized notifications in conjuction with scanners). Furthermore, it has the advantages of not requiring any scanners in the parent at all and also not being dependent on the child (and parent) being DNSSEC-signed. Knowledge of DNS NOTIFY and DNS Dynamic Updates and is assumed. DNS SIG(0) transaction signatures are documented in . In addition this Internet-Draft borrows heavily from the thoughts and problem statement from the Internet-Draft on Generalized DNS Notifications (work in progress).

Requirements Notation 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.

Is there a Use Case? Because of the drawbacks of CDS and CSYNC scanners they are unlikely to be able to fully automate the maintenance of delegation information in all parent zones. The primary reasons are the hard requirement on DNSSEC in the child zones and the complexity cost of operating the scanner infrastructure. In practice, scanners are likely mostly realistic for parent zones that are operated by well-resourced registries. All the parts of the DNS name space where the parent is smaller and more resource constrained would be able to automate the delegation management via this mechanism without the requirement of operating scanners. Also all parts of the name space where there are child zones that are not DNSSEC-signed would be able to use this. Obviously, also well-resourced parent zones with DNSSEC-signed child zones would be able to use this DNS UPDATE-based mechanism, but in those cases scanners plus generalized notifications would also work.

DNS NOTIFY versus DNS UPDATE DNS NOTIFY and DNS UPDATE messages share several properties and are used to address similar issues.

Similarities between NOTIFY and UPDATE Both NOTIFY and UPDATE are "push" rather than "pull" messages and therefore very efficient. Both NOTIFY and UPDATE are messages, in DNS packet format. They are used by one party (the sender) to inform another party (the recipient) that some piece of DNS information has changed and that as a consequence of this change the recipient of the message may want to also make a change to its DNS data. A NOTIFY (as per ) is only a hint and the recipient may ignore it. But if the recipient does listen to the NOTIFY it should make its own lookups to verify what has changed and whether that should trigger any changes in the DNS data provided by the recipient.

Generalized NOTIFY vs original NOTIFY This is a proposed extension to the use of NOTIFY. The extension covers using NOTIFY(CSYNC) to signal the publication of a CSYNC record in the child zone (prompting the parent zone to look it up and make a decison on whether to update the delegation information for the child zone based upon what is found. Another type is NOTIFY(CDS) which does the same, except it is used to prompt the parent to decide whether to update the child DS RRset (or not). A generalized NOTIFY is typically sent across a zone cut (from child to parent) and the recipient is likely a CSYNC or CDS scanner. In this case it is essentially a message that says:

Differencies between NOTIFY and UPDATE The difference between the UPDATE and the NOTIFY is that the UPDATE contains the exact change that should (in the opinion of the sender) be applied to the recipients DNS data. Furthermore, for secure Dynamic Updates, the message also contains proof why the update should be trusted (in the form of a digital signature by a key that the recipient trusts). In this document the term "Dynamic Update" or "DNS UPDATE" implies secure dynamic update. Furthermore this document implies that the signature algorithms are always based on asymmetric crypto keys, using the same algorithms as are being used for DNSSEC. I.e. by using the right algorithm the resulting signatures will be as strong as DNSSEC-signatures. DNS UPDATEs can be used to update any information in a zone (subject to the policy of the recipient). But in the special case where the data that is updated is the delegation information for a child zone and it is sent across a zone cut (i.e. the child sends it to the parent), it acts as a glorified generalized NOTIFY. The DNS UPDATE in this case is essentially a message that says:

Terminology

SIG(0)

An assymmetric signing algorithm that allows the recipient to only need to know the public key to verify a signature created by the senders private key.

Updating Delegation Information via DNS UPDATEs. This is not a new idea. The functionality to update delegation information in the parent zone via DNS UPDATE has been available for years in a least one DNS implementation (BIND9). However, while DNS UPDATE is used extensively inside organisations it has not seen much use across organisational boundaries. And zone cuts, almost by definition, usually cuts across such boundaries. When sending a DNS UPDATE it is necessary to know where to send it. Inside an organisation this information is usually readily available. But outside the organisation it is not. And even if the sender would know where to send the update, it is not at all clear that the destination is reachable to the sender (the parent primary is likely to be protected by firewalls and other measures). This constitutes a problem for using DNS UPDATES across zone cuts. Another concern is that traditionally DNS UPDATEs are sent to a primary nameserver, and if the update signture verifies the update is automatically applied to the DNS zone. This is often not an acceptable mechanism. The recipient may, for good reason, require additional policy checks and likely an audit trail. Finally, the change should in many cases not be applied to the running zone but rather to some sort of provisioning system or a database. This creates another problem for using DNS UPDATEs for managing delegation information. Both problems are addressed by the proposed mechanism for locating the recipient of a generalized NOTIFY.

Locating the Target for a generalized NOTIFY and/or DNS UPDATE. The generalized notifications I-D proposes a new RR type, tentatively with the mnemonic NOTIFY that has the following format:

where {parent zone} is the domain name of the parent zone and {target} is the domain name of the recipient of the NOTIFY. {RRtype} is typically "CDS" or "CSYNC" in the case where delegation information should be updated (there are also other uses of generalized notifications). Finally, {scheme} is a number to indicate the type of notification mechanism to use. Scheme=1 is defined as "send a generalized NOTIFY". Example for where children of parent. should send NOTIFY(CSYNC):

This record is looked up by the child primary nameserver at the time that the child primary is about to publish a new CSYNC record in the child zone (or the equivalent for a CDS). The interpretation is: Send a NOTIFY(CSYNC) to csync-scanner.parent. on port 5301

Locating the Target for a DNS UPDATE. This document proposes the definition of a new {scheme} for the same record that is used for generalized NOTIFY. Scheme=2 is here defined as "send a DNS UPDATE". Example:

This record is looked up by the child primary nameserver at the time that the delegation information for the child zone changes (typically causing the child to publish a new CSYNC record and/or a new CDS record). The interpretation is: Send a DNS UPDATE to ddns-receiver.parent. on port 5302

Limitation of Scope for the Proposed Mechanism DNS UPDATE is in wide use all over the world, for all sorts of purposes. It is not in wide use (if used at all) across organizational boundaries. This document only address the specific case of a child zone that makes a change in its DNS information that will require an update of the corresponding information in the parent zone. This includes: changes to the NS RRset changes to glue (if any) changes to the DS RRset (if any) Only for those specific cases is the descibed mechanism proposed.

Processing the UPDATE in the DNS UPDATE Receiver The receiver of the DNS UPDATE messages should implement a suitably strict policy for what updates are accepted (typically only allowing updates to the NS RRset, glue and DS RRset). Furthermore, it is strongly recommended that the policy is further tightened by only allowing updates to the delegation information of a child zone with the exact same name as the name of the SIG(0) key the signed the UPDATE request. I.e. an UPDATE request for the delegation information for the zone child.parent. should only be processed if it is signed by a SIG(0) key with the name child.parent. and the signature verifies correctly. Once the UPDATE has been verified to be correctly signed by a known key with the correct name and also adhere to the update policy it should be subjected to the same set of correctness tests as CDS/CSYNC scanner would have performed. If these requirements are also fulfilled the change may be applied to the parent zone in whatever manner the parent zone is maintained (as a text file, data in a database, via and API, etc).

Interpretation of the response to the DNS UPDATE. All DNS transactions are designed as a pair of messages and this is true also for DNS UPDATE. The interpretation of the different responses to DNS UPDATE are already fully documented in , section 2.2. In particular a response with rcode=5 ("REFUSED") should be interpreted as a permanent signal that DNS UPDATEs are not supported by the receiver. The case of no response is more complex, as it is not possible to know whether the DNS UPDATE actually reached the reciever (or was lost in transit) or the response was not sent (or lost in transit). For this reason it is suggested that a lack of response is left as implementation dependent. That way the implementation has sufficient freedom do chose a sensible approach. Eg. if the sender of the DNS UPDATE (like the primary nameserver of the child zone) only serves a single child, then resending the DNS UPDATE once or twice may be ok (to ensure that the lack of response is not due to packets being lost in transit). On the other hand, if the sender serves a large number of child zones below the same parent zone, then it may already know that the receiver for the DNS UPDATEs is not responding for any of the child zones, and then resending the update immediately is likely pointless.

Management of SIG(0) Public Keys Only the child should have access to the SIG(0) private key. The corresponding SIG(0) public key doesn't have to be published in DNS, it only needs to be available to the parent DNS UPDATE Receiver. Keeping all the public SIG(0) keys for different child zones in some sort of database is perfectly fine.

Bootstrapping the SIG(0) Public Key Into the DNS UPDATE Receiver The primary audience for this DNS UPDATE based synchronization mechanism is "non-registries". In those cases there is by definition some mechanism in place to communicate information from the child to the parent, be it email, a web form, pieces of paper or something else. The same mechanism can be extended to also be used to communicate the initial SIG(0) public key from the child to the parent. Should a "registry" parent want to support this mechanism (as a service to its unsigned children) then the interface is usually EPP and would require the implementation of a new EPP extension, which is clearly doable.

Rolling the SIG(0) Key Once the parent DNS UPDATE Receiver has the key, the child can update it via a DNS UPDATE just like updating the NS RRset, the DS RRset or the glue in the parent zone (assuming a suitable DNS UPDATE policy in the parent). I.e. only the initial bootstrapping of the key is an issue.

Security Considerations. Any fully automatic mechanism to update the contents of a DNS zone opens up a potential vulnerability should the mechanism not be implemented correctly. In this case the definition of "correct" is a question for the receiver of the DNS UPDATE. The receiver should validate the authenticity of the DNS UPDATE and then do the same checks and verifications as a CDS or CSYNC scanner does. The difference from the scanner is only in the validation: single SIG(0) signature by a key that the receiver trusts vs DNSSEC signature that chains back to a DNSSEC trust anchor that a scanner trusts.

IANA Considerations. None.

Acknowledgements. Peter Thomassen and I together came up with the location mechanism for the generalized notifications, which this draft relies upon. Mark Andrews provided the initial inspiration for writing some code to experiment with the combination of the location mechanism from the generalised notifications with DNS UPDATEs across zone cuts.

This memo describes the NOTIFY opcode for DNS, by which a master server advises a set of slave servers that the master's data has been changed and that a query should be initiated to discover the new data. [STANDARDS-TRACK] Using this specification of the UPDATE opcode, it is possible to add or delete RRs or RRsets from a specified zone. Prerequisites are specified separately from update operations, and can specify a dependency upon either the previous existence or nonexistence of an RRset, or the existence of a single RR. [STANDARDS-TRACK] This document proposes a method for performing secure Domain Name System (DNS) dynamic updates. [STANDARDS-TRACK] This document describes the minor but non-interoperable changes in Request and Transaction signature resource records ( SIG(0)s ) that implementation experience has deemed necessary. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This memo describes a method of encapsulating IPX datagrams within UDP packets so that IPX traffic can travel across an IP internet. [STANDARDS-TRACK] This memo defines objects for managing DS1 Interface objects for use with the SNMP protocol. [STANDARDS-TRACK]

Change History (to be removed before publication) draft-johani-dnsop-delegation-mgmt-via-ddns-00

• Initial public draft.