Internet Engineering Task Force S. Huque Internet-Draft P. Aras Intended status: Informational Salesforce Expires: September 04, 2018 March 03, 2018 Multi Provider DNSSEC models draft-huque-dnsop-multi-provider-dnssec-01 Abstract Many enterprises today employ the service of multiple DNS providers to distribute their authoritative DNS service. Deploying DNSSEC in such an environment can have some challenges depending on the configuration and feature set in use. This document will present several deployment models that may be suitable. 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 http://datatracker.ietf.org/drafts/current/. 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 September 04, 2018. Copyright Notice Copyright (c) 2018 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 (http://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 extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Huque & Aras Expires September 04, 2018 [Page 1] Internet-Draft Multi Provider DNSSEC models March 2018 Table of Contents 1. Introduction and Motivation . . . . . . . . . . . . . . . . . 2 2. Deployment Models . . . . . . . . . . . . . . . . . . . . . . 2 2.1. Serve Only model . . . . . . . . . . . . . . . . . . . . 2 2.2. Sign and Serve model . . . . . . . . . . . . . . . . . . 3 2.2.1. Model 1 . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.2. Model 2 . . . . . . . . . . . . . . . . . . . . . . . 4 2.2.3. Other Models . . . . . . . . . . . . . . . . . . . . 4 2.3. Inline Signing model . . . . . . . . . . . . . . . . . . 4 3. Signing Algorithm Considerations . . . . . . . . . . . . . . 5 4. Validating Resolver Behavior . . . . . . . . . . . . . . . . 5 5. Key Rollover Considerations . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction and Motivation Many enterprises today employ the service of multiple DNS providers to distribute their authoritative DNS service. Two providers are fairly typical and this allows the DNS service to survive a complete failure of any single provider. This document outlines some possible models of DNSSEC [RFC4033] [RFC4034] [RFC4035] deployment in such an environment. 2. Deployment Models The two main models discussed are (1) where the zone owner runs a master signing server and essentially treats the managed DNS providers as secondary servers, the "Serve Only" model, and (2) where the managed DNS providers each act like primary servers, signing data received from the zone owner and serving it out to DNS queriers, the "Sign and Serve" model. 2.1. Serve Only model The most straightforward deployment model is one in which the zone owner runs a primary master DNS server, and manages the signing of zone data. The master server uses DNS zone transfer mechanisms (AXFR /IXFR) to distribute the signed zone to multiple DNS providers. Huque & Aras Expires September 04, 2018 [Page 2] Internet-Draft Multi Provider DNSSEC models March 2018 This is also arguably the most secure model because the zone owner holds the private signing keys. The managed DNS providers cannot serve bogus data (either maliciously or because of compromise of their systems) without detection by validating resolvers. One notable limitation of this model is that it may not work with DNS authoritative server configurations that use certain non-standardized DNS features. Some of these features like DNS based Global Server Load Balancing (GSLB), dynamic failover pools, etc. rely on querier specific responses, or responses based on real-time state examination, and so, the answer and corresponding signature has to be determined at the authoritative server being queried, at the time of the query, or both. (If all possible answer sets for these features are known in advance, it would be possible to pre-compute these answer sets and signatures, but the DNS zone transfer protocol cannot be used to distinguish or transfer such data sets, or the rules used to select among the possible answers.) 2.2. Sign and Serve model In this category of models, multiple providers each independently sign and serve the same zone. The zone owner typically uses provider-specific APIs to update zone content at each of the providers, and relies on the provider to perform signing of the data. A key requirement here is to manage the contents of the DNSKEY and DS RRset in such a way that validating resolvers always have a viable path to authenticate the DNSSEC signature chain no matter which provider they query and obtain responses from. These models can support DNSSEC even for the non-standard features mentioned previously, if the DNS providers have the capability of signing the response data generated by those features. Since these responses are often generated dynamically at query time, one method is for the provider to perform online signing (also known as on-the- fly signing). However, another possible approach is to pre-compute all the possible response sets and associated signatures and then algorithmically determine at query time which response set needs to be returned. In these models, the function of coordinating the DNSKEY or DS RRset does not involve the providers communicating directly with each other, which they are unlikely to do since they typically have a contractual relationship only with the zone owner. The following descriptions consider the case of two DNS providers, but the model is generalizable to any number. Huque & Aras Expires September 04, 2018 [Page 3] Internet-Draft Multi Provider DNSSEC models March 2018 2.2.1. Model 1 o Zone owner holds the KSK and manages the DS record. o Each provider has their own ZSK which is used to sign data. o Providers have an API that owner uses to query the ZSK. public key, and insert a combined DNSKEY RRset that includes both ZSKs and the KSK, signed by the KSK. o Key rollovers need coordinated participation of the zone owner to update and re-sign the DNSKEY RRset. 2.2.2. Model 2 o Each provider has their own KSK and ZSK. o Each provider also includes the ZSK of the other provider - delivered to them by the zone owner via some API mechanism. o DNSKEY RRset is signed independently by each provider using their own KSK. o Zone owner manages the DS RRset that includes both KSKs. o KSK rollovers need coordinated participation of the zone owner to update the DS RRset. 2.2.3. Other Models Possible models in which KSK and/or ZSK key pairs are shared across providers are not currently discussed. Preliminary discussion with some providers has revealed that this is not a mode all of them are comfortable with, as they do not want to share signing keys with other parties. 2.3. Inline Signing model In this model, the zone owner runs a master server but does not perform zone signing, instead pushing out the zone (typically via zone transfer mechanisms) to multiple providers, and relying on those providers to sign the zone data before serving them out. This model has to address the same set of requirements as the Sign-and-Serve model regarding managing the DNSKEY and DS RRsets. However, assuming standardized zone transfers mechanisms are being used to push out the zone to the providers, it likely also has the limitation that non- standardized DNS features cannot be supported or signed. This model is not discussed further. Huque & Aras Expires September 04, 2018 [Page 4] Internet-Draft Multi Provider DNSSEC models March 2018 3. Signing Algorithm Considerations [TBD: at the very least we have to note whether any or all of these schemes require algorithms to be the same or not, or benefit from algorithms being the same. Current DNS specifications indicate that if there are multiple algorithms in the DNSKEY RRset, then data records need to be signed with at least one of each algorithm, (how does that work with online signing?). Multiple signatures per record set is a cost that probably few operators want to bear.] 4. Validating Resolver Behavior From the point of view of the Validating Resolver, the Sign and Serve models (Section 2.2), that employ multiple providers signing the same zone data with distinct keys, are the most interesting. In these models, for each provider, the Zone Signing Keys of the other providers are imported into the DNSKEY RRset and the DNSKEY RRset is re-signed. If this is not done, the following situation can arise (assuming two providers A and B): o The validating resolver follows a referral (delegation) to the zone in question. o It retrieves the zone's DNSKEY RRset from one of provider A's nameservers. o At some point in time, the resolver attempts to resolve a name in the zone, while the DNSKEY RRset received from provider A is still viable in its cache. o It queries one of provider B's nameservers to resolve the name, and obtains a response that is signed by provider B's ZSK, which it cannot authenticate because this ZSK is not present in its cached DNSKEY RRset for the zone that it received from provider A. o The resolver will not accept this response. It may still be able to ultimately authenticate the name by querying other nameservers for the zone until it elicits a response from one of provider A's nameservers. But it has incurred the penalty of additional roundtrips with other nameservers, with the corresponding latency and processing costs. The exact number of additional roundtrips depends on details of the resolver's nameserver selection algorithm and the number of nameservers configured at provider B. o Zone owners will want to deploy a DNS service that responds as efficiently as possible with validatable answers, and hence it is important that the DNSKEY RRset is maintained with the ZSKs of all participating providers. Huque & Aras Expires September 04, 2018 [Page 5] Internet-Draft Multi Provider DNSSEC models March 2018 As long as the DNSKEY RRset at each provider contains the active ZSKs of all the providers, resolvers can validate a response no matter which provider's nameservers it came from. Details of how the DNSKEY RRset itself is validated differs. In Sign and Serve model 1 (Section 2.2.1), one unique KSK managed by the Zone Owner signs an identical DNSKEY RRset deployed at each provider, and the signed DS record in the parent zone refers to this KSK. In Sign and Serve model 2 (Section 2.2.2), each provider has a distinct KSK and signs the DNSKEY RRset with it. The Zone Owner deploys a DS RRset at the parent zone that contains multiple DS records, each referring to a distinct provider's KSK. Hence it does not matter which provider's nameservers the resolver obtains the DNSKEY RRset from, the signed DS record in each model can authenticate the associated KSK. 5. Key Rollover Considerations TBD 6. IANA Considerations This document includes no request to IANA. 7. Security Considerations [TBD] 8. References 8.1. Normative References [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Protocol Modifications for the DNS Security Extensions", RFC 4035, March 2005. 8.2. Informative References Huque & Aras Expires September 04, 2018 [Page 6] Internet-Draft Multi Provider DNSSEC models March 2018 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. [RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC Operational Practices, Version 2", RFC 6781, DOI 10.17487/ RFC6781, December 2012, . Authors' Addresses Shumon Huque Salesforce Email: shuque@gmail.com Pallavi Aras Salesforce Email: paras@salesforce.com Huque & Aras Expires September 04, 2018 [Page 7]