Automating DNS Delegation Management via DDNS
draft-johani-dnsop-delegation-mgmt-via-ddns-04
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Johan Stenstam , Erik Bergström , Leon Fernandez | ||
| Last updated | 2024-11-02 (Latest revision 2024-10-21) | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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draft-johani-dnsop-delegation-mgmt-via-ddns-04
DNSOP Working Group J. Stenstam
Internet-Draft E. Bergström
Intended status: Standards Track L. Fernandez
Expires: 24 April 2025 The Swedish Internet Foundation
21 October 2024
Automating DNS Delegation Management via DDNS
draft-johani-dnsop-delegation-mgmt-via-ddns-04
Abstract
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 (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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 4
2. Is there a Use Case? . . . . . . . . . . . . . . . . . . . . 4
3. DNS NOTIFY versus DNS UPDATE . . . . . . . . . . . . . . . . 4
3.1. Similarities between NOTIFY and UPDATE . . . . . . . . . 4
3.2. Differencies between NOTIFY and UPDATE . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Updating Delegation Information via DNS UPDATEs. . . . . . . 6
6. Locating the Target for a generalized NOTIFY and/or DNS
UPDATE. . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Limitation of Scope for the Proposed Mechanism . . . . . . . 8
8. The DNS UPDATE Receiver . . . . . . . . . . . . . . . . . . . 8
8.1. Processing the UPDATE in the DNS UPDATE Receiver . . . . 8
9. Interpretation of the response to the DNS UPDATE. . . . . . . 9
9.1. RCODE NOERROR . . . . . . . . . . . . . . . . . . . . . . 9
9.2. RCODE REFUSED . . . . . . . . . . . . . . . . . . . . . . 9
9.3. RCODE BADKEY . . . . . . . . . . . . . . . . . . . . . . 9
9.4. No response to a DNS UPDATE . . . . . . . . . . . . . . . 9
10. Management of SIG(0) Public Keys . . . . . . . . . . . . . . 10
10.1. Bootstrapping the SIG(0) Public Key Into the DNS UPDATE
Receiver . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1.1. Signalling That Manual Bootstrap is Required or
Requested . . . . . . . . . . . . . . . . . . . . . . 11
10.1.2. Automatic Bootstrap of the SIG(0) Public Key . . . . 11
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10.1.3. Automatic Bootstrap When Child Zone is
DNSSEC-signed . . . . . . . . . . . . . . . . . . . . 11
10.1.4. Automatic Bootstrap When Child Zone is unsigned . . 12
10.2. Rolling the SIG(0) Key . . . . . . . . . . . . . . . . . 12
10.3. Re-bootstrapping In Case of Errors . . . . . . . . . . . 13
11. Communication Between Child and Parent UPDATE Receiver . . . 13
11.1. Communication in Case of Errors . . . . . . . . . . . . 14
11.2. Communication To Inquire State . . . . . . . . . . . . . 14
12. Scalability Considerations . . . . . . . . . . . . . . . . . 15
13. Security Considerations. . . . . . . . . . . . . . . . . . . 15
14. IANA Considerations. . . . . . . . . . . . . . . . . . . . . 16
15. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . 16
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
16.1. Normative References . . . . . . . . . . . . . . . . . . 16
16.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Change History (to be removed before publication) . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. 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.
[I-D.ietf-dnsop-generalized-notify] proposes 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.
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Knowledge of DNS NOTIFY [RFC1996] and DNS Dynamic Updates [RFC2136]
and [RFC3007] is assumed. DNS SIG(0) transaction signatures are
documented in [RFC2931]. In addition this Internet-Draft borrows
heavily from the thoughts and problem statement from the Internet-
Draft on Generalized DNS Notifications (work in progress).
1.1. 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 [RFC2119] [RFC8174] when, and only
when, they appear in all capitals, as shown here.
2. 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.
3. DNS NOTIFY versus DNS UPDATE
DNS NOTIFY and DNS UPDATE messages share several properties and are
used to address similar issues.
3.1. Similarities between NOTIFY and UPDATE
Both NOTIFY and UPDATE are "push" rather than "pull" messages and
therefore very efficient.
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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 [RFC1996]) 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.
3.2. 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:
"the delegation information for this child zone has changed; here
is the exact change; here is the proof that the change is
authentic, please verify this signature"
4. 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.
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5. Updating Delegation Information via DNS UPDATEs.
This is not a new idea. There is lots of prior art and prior
documents, including the expired I-D.andrews-dnsop-update-parent-
zones-04.
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.
6. Locating the Target for a generalized NOTIFY and/or DNS UPDATE.
Section 3 of [I-D.ietf-dnsop-generalized-notify] proposes a new RR
type, tentatively with the mnemonic DSYNC, that has the following
format:
{qname} IN DSYNC {RRtype} {scheme} {port} {target}
where {target} is the domain name of the recipient of the NOTIFY
message. {RRtype} is typically "CDS" or "CSYNC" in the case where
delegation information should be updated (there are also other uses
of generalized notifications).
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Finally, {scheme} is an 8 bit unsigned integer to indicate the type
of notification mechanism to use. Scheme=1 is defined "NOTIFY", as
in "send a generalized NOTIFY to {target} on port {port}".
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 "UPDATE", as in "send a DNS UPDATE to {target} on port {port}".
When parsing or presenting DNS zone data the 8 bit unsigned integer
"2" should be replaced by the string "UPDATE", as in the examples
below.
Apart from defining a new scheme to specify the mechanism "UPDATE"
(rather than the mechanism "NOTIFY") this document does not say
anything about what Qname to look up or what RR type. The UPDATE
mechanism should use exactly the same method of locating the target
of the UPDATE as is used for generalized NOTIFY.
This lookup addresses the first issue with using DNS UPDATE across
organizational boundaries.
Example 1: a parent zone announces support for DNS UPDATE as a
mechanism for delegation synchronization for all child zones:
_dsync.parent. IN DSYNC ANY 2 5302 ddns-receiver.parent.
Example 2: a parent zone announces support different DNS UPDATE
targets on a per-child basis
childA._dsync.parent. IN DSYNC ANY 2 5302 ddns-receiver.registrar1.
childB._dsync.parent. IN DSYNC ANY 2 5302 ddns-receiver.registrar3.
childC._dsync.parent. IN DSYNC ANY 2 5302 ddns-receiver.registrar2.
The DSYNC RRset is looked up, typically by the child primary name
server or by a separate agent for the child, at the time that the
delegation information for the child zone changes in some way that
would prompt an update in the parent zone. When the {scheme} is
"UPDATE" (i.e. the number 2 in the wire protocol) the interpretation
is:
Send a DNS UPDATE to the IP address for the name {target} on port
5302, where {target} is the domain name in the right-hand side of the
DSYNC record that matches the qname in the DNS query.
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7. 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 across organizational boundaries.
This document only address the specific case of a child zone that
makes a change in its DNS delegation 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 described mechanism proposed.
8. The DNS UPDATE Receiver
While the simplest design is to send the DNS UPDATEs to the primary
name server of the parent it will in most cases be more interesting
to send them to a separate UPDATE Receiver. To separate the primary
name server from the UPDATE Receiver, use a {target} with addresses
separate from the addresses of the primary name server.
8.1. 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 DNS UPDATE message has been verified to be correctly signed
by a known and trusted 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).
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9. 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 fully documented in [RFC2136], section
2.2.
9.1. RCODE NOERROR
A response with rcode=0 ("NOERROR") should be interpreted as a
confirmation that the DNS UPDATE has been received and accepted.
I.e. the change to the parent DNS data should be expected to be
published in the parent zone at some future time.
9.2. RCODE REFUSED
A response with rcode=5 ("REFUSED") should be interpreted as a
permanent signal that DNS UPDATEs are not supported by the receiver.
This would indicate a parent misconfiguration, as the UPDATE should
not be sent unless the parent has announced support for DNS UPDATE
via publication of an appropriate target location record.
9.3. RCODE BADKEY
A response with rcode=17 ("BADKEY") should be interpreted as a
definitive statement that the DNS UPDATE Receiver does not have
access to the public SIG(0) key needed for signature verification.
In this case the child should fall back to bootstrap of the SIG(0)
public key into the DNS UPDATE Receiver, see below.
9.4. No response to a DNS UPDATE
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 message (like the primary name server 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.
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10. Management of SIG(0) Public Keys
Only the child should have access to the SIG(0) private key. The
corresponding SIG(0) public key should preferably be published in
DNS, but it doesn't have have to be. The SIG(0) public key 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.
10.1. Bootstrapping the SIG(0) Public Key Into the DNS UPDATE Receiver
Bootstrap of the child public SIG(0) key to be trusted by the UPDATE
Receiver may be done either manually or automatically. Manually may
in various cases be the preferred method, especially in the case of
non-registry parents with a small number of child delegations.
If the UPDATE Receiver only supports manual bootstrap, then that is
what will happen (apart from informing the child about this policy).
If the child wants to enforce manual bootstrap it needs to request
this from the UPDATE Receiver.
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.
Regardless of whether manual bootstrap or automatic bootstrap is to
be used (subject to the UPDATE Receiver policy), the bootstrap must
be initiated. This is done by the child issuing a self-signed DNS
UPDATE to the parent containing:
DEL child.parent. {ttl} ANY KEY
ADD child.parent. {ttl} IN KEY ...
The first record is an instruction to delete any previous keys for
this child (CLASS=ANY in a DNS UPDATE is a request to delete an
entire RRset). The second is an instruction to add the new key.
When receiving such a message (where the self-signature validates)
the parent UPDATE Reciever SHOULD mark that key as "known" (but not
yet trusted) and then either put that key into a queue for later look
up and validation of the corresponding KEY record (if supporting
automatic bootstrap) or put that key into a queue for subsequent
manual validation and verification.
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10.1.1. Signalling That Manual Bootstrap is Required or Requested
[I-D.berra-dnsop-keystate] describes a mechanism by which the child
may communicate "Key State" to the UPDATE Receiver. If the child
supports this mechanism then a KeyState OPT MUST be included in the
initial key upload (the self-signed UPDATE containing the public
key). The child MAY include a KeyState OPT containing the KEY-STATE
for "Manual bootstrap requested" (value=10). The UPDATE Receiver
SHOULD honour this request and not perform automatic bootstrap for
this child and this key.
Likewise, in the response to the initial key upload, if the UPDATE
contained a KeyState OPT, then the UPDATE Receiver has the ability to
signal the requirement that the child SIG(0) key is manually
bootstrapped (verified) by including a KeyState OPT containing the
KEY-STATE for "Manual bootstrap required" (value=8). If a KeyState
OPT from the UPDATE Receiver is included in the response then the
child MUST validate this message using the SIG(0) public key of the
UPDATE Receiver. If the response is unsigned it MUST be ignored. If
the response valdiates then the child SHOULD signal this information
to an operator, to resolve manually.
10.1.2. Automatic Bootstrap of the SIG(0) Public Key
Automated bootstrapping is also possible, subject to the policy of
the UPDATE Receiver. The basic idea is to publish the public SIG(0)
key as a KEY record at the child apex prior to the initial key
upload. Then the UPDATE Receiver (or an agent) may look that KEY up
for subsequent validation.
10.1.3. Automatic Bootstrap When Child Zone is DNSSEC-signed
If the child zone is DNSSEC-signed (including a signed delegation via
a DS record), then the KEY record containing the SIG(0) public key
can be looked up and validated by the DNS UPDATE Receiver.
child.parent. IN KEY ...
child.parent. IN RRSIG KEY ...
In case of validation success the key SHOULD be promoted to "trusted"
by the UPDATE Receiver. At this point any old keys should be
deleted.
In case of validation failure (or absence of a DNSSEC signature) the
SIG(0) SHOULD NOT be promoted to the set of keys that the UPDATE
Receiver trusts and any old keys MUST be kept.
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10.1.4. Automatic Bootstrap When Child Zone is unsigned
The bootstrap problem in the unsigned case is essentially identical
to the "automatic DNSSEC Bootstrap via CDS" service a la [RFC8078]
that multiple TLD registries provide today.
Hence, to bootstrap the public SIG(0) key for a child zone it is
possible for the parent use a "bootstrap policy" a la:
* Look up the KEY RRset in the child zone. Compare to the child KEY
received in the self-signed DNS UPDATE.
* To mitigate possible spoofing, do the look up of the child KEY
RRset from multiple vantage points, at multiple times. The child
KEY RRset must be consistent over time and space.
* Make spoofed responses even more difficult by adding a requirement
to use a more stable transport, like TCP (or in the future DOT,
DOH or DOQ once those become more generally available for DNS
queries to authoritative servers) in addition to UDP. The child
KEY RRset must be consistent over all tested transports.
* If the received KEY RRset is consistent from multiple vantage
points and multiple times then it is considered authentic and
promoted by the parent's UPDATE Receiver from "known" to "trusted"
SIG(0) key for the child. At this point any old SIG(0) public
keys for the child should be deleted.
Should a "registry" parent want to support this mechanism (as a
service to its unsigned children) then a likely model is that the
target of the DNS UPDATE is operated by the registrar (or possibly
that the DNS UPDATE is forwarded to the registrar). The registrar
performs its normal verifications of a change and then transforms the
update into an EPP [RFC5730] transaction to communicate it to the
registry.
10.2. Rolling the SIG(0) Key
Once the parent (or registrar) 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.
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Note, however, that the alternative of re-bootstrapping (by whatever
bootstrapping mechanism was used) in case of a key compromise may be
a better alternative to the parent supporting key rollover for child
SIG(0) keys. The decision of whether to allow SIG(0) key rollover
via DNS UPDATE is left as parent-side policy.
10.3. Re-bootstrapping In Case of Errors
Sometimes things get out of sync in spite of all efforts. In this
case it could be an operator error in the parent end losing the child
public key or it could be an error in the child end losing the
private key. Another possibility could be a key rollover that for
some reason didn't sync correctly.
If [I-D.berra-dnsop-keystate] is supported then the child can inquire
with the UPDATE Receiver about the KeyState of the SIG(0) key it
would use in an UPDATE request.
In all such cases, as soon as the child becomes aware of the problem
it should simply re-bootstrap by the same mechanism as used
initially. The self-signed DNS UPDATE that starts the bootstrapping
process contains a
DEL child.parent. {ttl} ANY KEY
and that is an instruction to the parent UPDATE Receiver to delete
any SIG(0) public keys for this child (and after that start the
process to validate the new key).
Note that when receiving such a self-signed DNS UPDATE the parent
MUST NOT delete any old keys until the new key has been validated and
therefore promoted to "trusted". This is needed and important to
avoid the potential attack vector of an adversary causing a parent to
invalidate the child key by just sending a self-signed bootstrap
UPDATE (which will not validate, but if the old key is deleted then
the harm would already be done).
11. Communication Between Child and Parent UPDATE Receiver
There are two cases where communication between child and parent
UPDATE Receiver would benefit greatly from some additional
information.
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11.1. Communication in Case of Errors
An error response from the parent UPDATE Receiver would be improved
by more detail provided via a set of new Extended DNS Error Codes
[RFC8914]. In particular, it would be useful to be able to express
the following "states":
* "SIG(0) key is known, but not yet trusted": indicating that
bootstrap of the key is not yet complete. Waiting may resolve the
issue.
* "SIG(0) key is known, but validation failed": indicating that
bootstrap has failed and waiting will not resolve the issue.
* "Automatic bootstrap of SIG(0) keys not supported; manual
bootstrap required": indicating that while the parent does support
delegation sychronization via DNS UPDATE, it does only support
manual bootstrap.
11.2. Communication To Inquire State
Extended DNS Errors [RFC8914] provides an excellent mechanism for
adding more detail to error responses. However it is, intentionally,
limited to:
* returning extra information from the receiver to the original
sender. It is not possible to "send" information, only "return"
information.
* no information except the actual error code is meant for automatic
processing. it is therefore not possible to communicate things
like, eg. a KeyId via EDE.
The communication between child and parent would gain from the
addition of the ability to also send inquiries to the parent:
* For the child to be able to inquire about the state of the parent.
I.e. "I operate under the assumption that the key {key} is known
and trusted by you (the parent). Is this correct?"
* For the child to inquire about things: "Do you (parent) support
automatic bootstrapping or not?"
[I-D.berra-dnsop-keystate] is being proposed as a mechanism to
improve the communication between child and parent, both in the error
case and in the inquiry case. If that draft is supported then all of
the above examples would travel as a new "KeyState codes" in a
KeyState OPT as specified in [I-D.berra-dnsop-keystate].
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12. Scalability Considerations
The primary existing mechanism for automatic synchronization of DNS
delegation information is based on parent-side "scanning" of the
child zones for CDS and/or CSYNC RRsets, performing DNSSEC validation
on the result and then, in the CSYNC case, based on the result, issue
and validate a potentially large number of additional DNS queries,
all of which must be DNSSEC validated. This makes a CDS/CSYNC
scanner for a parent with a significant number of delegations a
complex and resource consuming service. Among the issues are rate-
limiting by large DNS operators and inherent difficulties in issuing
millions of recursive DNS queries where all received data must be
validated.
By comparision, the DNS UPDATE based mechanism for automatic
synchronization shifts most of the effort to the child side. It is
the child that is responsible for detecting the need to update the
delegation information in the parent zone (which makes sense as it is
the child that has made a change and therefore, in many cases,
already "knows"). It is the child rather than the parent that
computes what records should be added or removed. All of this is
good for scalability.
Furthermore, the information collection and validation effort for the
UPDATE Receiver is restricted to validation of a single DNS message,
using a SIG(0) key that the UPDATE Receiver already has.
Hence, as the data collection and validation is much simplified the
task of the UPDATE Receiver is mostly focused on the policy issues of
whether to approve the UPDATE or not (i.e. the same process that a
CDS and/or CSYNC scanner follows).
13. 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 UPDATE Receiver trusts vs DNSSEC signatures that chain
back to a DNSSEC trust anchor that the validator trusts.
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Another issue of concern is whether a parent-side service that
provides support for changes to child delegation information via DNS
UPDATE is open for potential denial-of-service attacks. The answer
is likely no, as it is possible to have a very strict rate-limiting
policy based on the observation that no child zone should have a
legitimate need to change its delegation information frequently.
Furthermore, as the location of the UPDATE Receiver can be separated
from any parent name server even in the worst case the only service
that can be subject to an attack is the UPDATE Receiver itself, which
is a service that previously did not exist.
14. IANA Considerations.
IANA is requested to assign a new "scheme" value to the registry for
"DSYNC Location of Synchronization Endpoints" as follows:
Reference (this document)
+========+========+=======================+=================+
| RRtype | Scheme | Purpose | Reference |
+========+========+=======================+=================+
| ANY | 2 | Delegation management | (this document) |
+--------+--------+-----------------------+-----------------+
Table 1
15. 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.
* Stefan Ubbink helped me realize the need to also cater for the
case of re-bootstrapping if or when things got out of sync for
some reason.
16. References
16.1. Normative References
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[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
August 1996, <https://www.rfc-editor.org/info/rfc1996>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997,
<https://www.rfc-editor.org/info/rfc2136>.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>.
[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
<https://www.rfc-editor.org/info/rfc3007>.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
<https://www.rfc-editor.org/info/rfc5730>.
[RFC8078] Gudmundsson, O. and P. Wouters, "Managing DS Records from
the Parent via CDS/CDNSKEY", RFC 8078,
DOI 10.17487/RFC8078, March 2017,
<https://www.rfc-editor.org/info/rfc8078>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/info/rfc8914>.
16.2. Informative References
[I-D.berra-dnsop-keystate]
Bergström, E., Fernandez, L., and J. Stenstam, "Signalling
Key State Via DNS EDNS(0) OPT", Work in Progress,
Internet-Draft, draft-berra-dnsop-keystate-00, 21 October
2024, <https://datatracker.ietf.org/doc/html/draft-berra-
dnsop-keystate-00>.
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[I-D.ietf-dnsop-generalized-notify]
Stenstam, J., Thomassen, P., and J. R. Levine,
"Generalized DNS Notifications", Work in Progress,
Internet-Draft, draft-ietf-dnsop-generalized-notify-03, 21
October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-dnsop-generalized-notify-03>.
Appendix A. Change History (to be removed before publication)
* draft-johani-dnsop-delegation-mgmt-via-ddns-04
Reworked the section on automatic bootstrapping a la RFC8078.
Added a section on re-bootstrapping the SIG(0) key with the parent
after problems.
Added text on the importance of augmenting error responses using
EDE (RFC8914).
Added text on the insufficiency of RFC8914 for child-to-parent
communication and a reference to the (upcoming) draft on a new OPT
code to alleviate this.
* draft-johani-dnsop-delegation-mgmt-via-ddns-03
Update the draft based on the excellent dnsdir review of draft-
ietf-dnsop-generalized-notify-01 by Patrick Mevsek.
Expand the section on alternatives for initial bootstrap to
suggest a mechanism similar to what is used for automatic
bootstrap of DNSSEC signed delegations via multiple queries for
child the CDS RRset.
Added a section on scalability considerations.
Expanded the Security Considerations section with a paragraph on
the potential for DDOS attacks aimed at the UPDATE Receiver.
* draft-johani-dnsop-delegation-mgmt-via-ddns-02
Update the references to the (updated) I-D for generalized
notifications.
Remove duplicated descriptions between the two drafts. It is
sufficient that the generalized notification draft describes the
mechanics.
* draft-johani-dnsop-delegation-mgmt-via-ddns-01
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Change the RRtype from the original "NOTIFY" to the proposed
"DSYNC"
Expand the description of how to interpret different RCODE
responses to the UPDATE. Expand the description of bootstrapping
alternatives. Change the mnemonic of the RR type used from
"NOTIFY" to "DSYNC" in the examples.
* draft-johani-dnsop-delegation-mgmt-via-ddns-00
Initial public draft.
Authors' Addresses
Johan Stenstam
The Swedish Internet Foundation
Sweden
Email: johan.stenstam@internetstiftelsen.se
Erik Bergström
The Swedish Internet Foundation
Sweden
Email: erik.bergstrom@internetstiftelsen.se
Leon Fernandez
The Swedish Internet Foundation
Sweden
Email: leon.fernandez@internetstiftelsen.se
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