--- 1/draft-ietf-dnsop-qname-minimisation-00.txt 2015-02-15 03:14:55.578215411 -0800 +++ 2/draft-ietf-dnsop-qname-minimisation-01.txt 2015-02-15 03:14:55.598215899 -0800 @@ -1,165 +1,194 @@ -Network Working Group S. Bortzmeyer +Domain Name System Operations (dnsop) Working Group S. Bortzmeyer Internet-Draft AFNIC -Intended status: Informational October 22, 2014 -Expires: April 25, 2015 +Intended status: Experimental February 15, 2015 +Expires: August 19, 2015 DNS query name minimisation to improve privacy - draft-ietf-dnsop-qname-minimisation-00 + draft-ietf-dnsop-qname-minimisation-01 Abstract This document describes one of the techniques that could be used to - improve DNS privacy (see [I-D.bortzmeyer-dnsop-dns-privacy]), a + improve DNS privacy (see [I-D.ietf-dprive-problem-statement]), a technique called "qname minimisation". Discussions of the document should take place on the DNSOP working group mailing list [dnsop]. 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 April 25, 2015. + This Internet-Draft will expire on August 19, 2015. Copyright Notice - Copyright (c) 2014 IETF Trust and the persons identified as the + Copyright (c) 2015 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. Table of Contents 1. Introduction and background . . . . . . . . . . . . . . . . . 2 2. Qname minimisation . . . . . . . . . . . . . . . . . . . . . 2 3. Operational considerations . . . . . . . . . . . . . . . . . 3 - 4. Other advantages . . . . . . . . . . . . . . . . . . . . . . 4 + 4. Performance implications . . . . . . . . . . . . . . . . . . 5 5. Security considerations . . . . . . . . . . . . . . . . . . . 5 - 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 - 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 + 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 + 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 6 - Appendix A. An algorithm to find the zone cut . . . . . . . . . 6 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 + 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + Appendix A. An algorithm to find the zone cut . . . . . . . . . 7 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction and background The problem statement is exposed in - [I-D.bortzmeyer-dnsop-dns-privacy]. The terminology ("qname", - "resolver", etc) is also defined in this companion document. This - specific solution is not intended to completely solve the problem, - far from it. It is better to see it as one tool among a toolbox. + [I-D.ietf-dprive-problem-statement] TODO: add a reference to the + specific section when ietf-dprive-problem-statement will be published + as RFC. The terminology ("qname", "resolver", etc) is also defined + in this companion document. This specific solution is not intended + to fully solve the DNS privacy problem; instead, it should be viewed + as one tool amongst many. It follows the principle explained in section 6.1 of [RFC6973]: the less data you send out, the less privacy problems you'll get. 2. Qname minimisation The idea is to minimise the amount of data sent from the DNS resolver. When a resolver receives the query "What is the AAAA record for www.example.com?", it sends to the root (assuming a cold resolver, whose cache is empty) the very same question. Sending "What are the NS records for .com?" would be sufficient (since it will be the answer from the root anyway). To do so would be compatible with the current DNS system and therefore could be easily - deployable, since it is an unilateral change to the resolvers. + deployable, since it is an unilateral change to the resolvers, it + does not change the protocol. Because of that, resolver implementers + may do qname minmisation in slightly different ways. - If "minimisation" is too long, you can write it "m12n". + If "minimisation" is too long, you can write it "m10n". To do such minimisation, the resolver needs to know the zone cut - [RFC2181]. There is not a zone cut at every label boundary. If we - take the name www.foo.bar.example, it is possible that there is a - zone cut between "foo" and "bar" but not between "bar" and "example". - So, assuming the resolver already knows the name servers of .example, - when it receives the query "What is the AAAA record of - www.foo.bar.example", it does not always know if the request should - be sent to the name servers of bar.example or to those of example. - [RFC2181] suggests a method to find the zone cut (section 6), so - resolvers may try it. + [RFC2181]. Zone cuts do not necessarily exist at every label + boundary. If we take the name www.foo.bar.example, it is possible + that there is a zone cut between "foo" and "bar" but not between + "bar" and "example". So, assuming the resolver already knows the + name servers of .example, when it receives the query "What is the + AAAA record of www.foo.bar.example", it does not always know if the + request should be sent to the name servers of bar.example or to those + of example. [RFC2181] suggests a method to find the zone cut + (section 6), so resolvers may try it. Note that DNSSEC-validating resolvers already have access to this information, since they have to find the zone cut (the DNSKEY record set is just below, the DS record set just above). - It can be noted that minimising the amount of data sent also - partially addresses the case of a wire sniffer, not just the case of - privacy invasion by the servers. + Minimising the amount of data sent also, in part, addresses the case + of a wire sniffer as well the case of privacy invasion by the + servers. One should note that the behaviour suggested here (minimising the amount of data sent in qnames) is NOT forbidden by the [RFC1034] (section 5.3.3) or [RFC1035] (section 7.2). Sending the full qname to the authoritative name server is a tradition, not a protocol - requirment. + requirment. This tradition comes[mockapetris-history] from a desire + to optimize the number of requests, when the same name server is + authoritative for many zones in a given name (something which was + more common in the old days, where the same name servers served .com + and the root) or when the same name server is both recursive and + authoritative (something which is strongly discouraged now). + Whatever the merits of this choice at this time, the DNS is quite + different now. + + As mentioned before, there are several ways to implement qname + minimisation. Two main strategies are the aggressive one and the + lazy one. In the aggressive one, the resolver only sends NS queries + as long as it does not know the zone cuts. This is the safest, from + a privacy point of view. The lazy way "piggybacks" on the + traditional resolution code. It sends traditional full qnames and + learn the zone cuts from the referrals received, then switching to NS + queries. This leaks more data but probably requires less changes in + the existing resolver codebase. 3. Operational considerations The administrators of the forwarders, and of the authoritative name servers, will get less data, which will reduce the utility of the statistics they can produce (such as the percentage of the various - qtypes). On the other hand, it will decrease their legal - responsability, in many cases. + qtypes). On the other hand, it may decrease their legal + responsibility. Some broken name servers do not react properly to qtype=NS requests. - As an example of today, look at www.ratp.fr (not ratp.fr), which is - delegated to two name servers that reply properly to "A www.ratp.fr" - queries but send REFUSED to queries "NS www.ratp.fr". This behaviour - is a gross protocol violation and there is no need to stop improving - the DNS because of such brokenness. However, qname minimisation may - still work with such domains since they are only leaf domains (no - need to send them NS requests). Anyway, such setup breaks many - things (besides qname minimisation), it breaks negative answers as - the servers don't return the correct SOA. It also breaks anything - that depends on NS and SOA records existing at the top of the zone. + For instance, some authoritative name servers embedded in load + balancers reply properly to A queries but send REFUSED to NS queries. + REMOVE THIS SENTENCE BEFORE PUBLICATION: As an example of today, look + at www.ratp.fr (not ratp.fr). This behaviour is a gross protocol + violation, and there is no need to stop improving the DNS because of + such brokenness. However, qname minimisation may still work with + such domains since they are only leaf domains (no need to send them + NS requests). Such setup breaks more than just qname minimisation. + It breaks negative answers, since the servers don't return the + correct SOA, and it also breaks anything dependent upon NS and SOA + records existing at the top of the zone. + + A problem can also appear when a name server does not react properly + to ENT (Empty Non-Terminals). If ent.example.com has no resource + records but foobar.ent.example.com does, then ent.example.com is an + ENT. A query, whatever the qtype, for ent.example.com must return + NODATA (NOERROR / ANSWER: 0). However, some broken name servers + return NXDOMAIN for ENTs. REMOVE THIS SENTENCE BEFORE PUBLICATION: + As an example of today, look at com.akadns.net or www.upenn.edu with + its delegations to Akamai. If a resolver queries only + foobar.ent.example.com, everything will be OK but, if it implements + qname minimisation, it may query ent.example.com and get a NXDOMAIN. + See also section 3 of [I-D.vixie-dnsext-resimprove] for the other bad + consequences of this brokenness. Another way to deal with such broken name servers would be to try - with A requests (A being choosen because it is the most common and - hence the least revealing qtype). Instead of querying name servers - with a query "NS example.com", we could use "A _.example.com" and see - if we get a referral. + with A requests (A being chosen because it is the most common and + hence a qtype which will be always accepted, while a qtype NS may + ruffle the feathers of some middleboxes). Instead of querying name + servers with a query "NS example.com", we could use "A _.example.com" + and see if we get a referral. - Other strange and illegal practice may pose a problem: for instance, + Other strange and illegal practices may pose a problem: for instance, there is a common DNS anti-pattern used by low-end web hosters that also do DNS hosting that exploits the fact that the DNS protocol (pre-DNSSEC) allows certain serious misconfigurations, such as parent and child zones disagreeing on the location of a zone cut. Basically, they have a single zone with wildcards like: - ;; ANSWER SECTION: - *.com. 60 IN A 74.220.199.6 - - ; and: - - ;; ANSWER SECTION: - *.uk. 60 IN A 74.220.199.6 - - ; etc. + *.example. 60 IN A 192.0.2.6 (It is not known why they don't just wildcard all of "*." and be done with it.) This lets them turn up tons of web hosting customers without having to configure thousands of individual zones on their nameservers. They just tell the prospective customer to point their NS records at their nameservers, and the Web hoster doesn't have to provision anything in order to make the customer's domain resolve. @@ -167,86 +196,111 @@ instance for a deep domain name (like www.host.group.department.example.com where host.group.department.example.com is hosted on example.com's name servers). For such a name, a cold resolver will, depending how qname minimisation is implemented, send more queries. Once warm, there will be no difference with a traditional resolver. A possible solution is to always use the traditional algorithm when the cache is cold and then to move to qname minimisation. This will decrease the privacy a bit but will guarantee no degradation of performance. -4. Other advantages + Another useful optimisation may be, in the spirit of the HAMMER idea + [I-D.wkumari-dnsop-hammer] to probe in advance for the introduction + of zone cuts where none previously existed (i.e. confirm their + continued absence, or discover them.) - The main goal of qname minimisation is to improve privacy, by sending +4. Performance implications + + The main goal of qname minimisation is to improve privacy by sending less data. However, it may have other advantages. For instance, if a root name server receives a query from some resolver for A.CORP followed by B.CORP followed by C.CORP, the result will be three NXDOMAINs, since .CORP does not exist in the root zone. Under query - minimization, the root name servers would hear only one question (for - .CORP itself) to which they could answer NXDOMAIN, thus opening up a - negative caching opportunity in which the full resolver could know a - priori that neither B.CORP or C.CORP could exist. Thus in this - common case the total number of upstream queries under query + name minimisation, the root name servers would hear only one question + (for .CORP itself) to which they could answer NXDOMAIN, thus opening + up a negative caching opportunity in which the full resolver could + know a priori that neither B.CORP or C.CORP could exist. Thus in + this common case the total number of upstream queries under qname minimisation would be counter-intuitively less than the number of queries under the traditional iteration (as described in the DNS standard). + Qname minimisation may also improve look-up performance for TLD + operators. For a typical TLD, delegation-only, and with delegations + just under the TLD, a 2-label QNAME query is optimal for finding the + delegation owner name. + 5. Security considerations No security consequence (besides privacy improvment) is known at this time. 6. Acknowledgments - Thanks to Olaf Kolkman for the original idea. Thanks to Mark Andrews - and Francis Dupont for the interesting discussions. Thanks to Mohsen - Souissi for proofreading. Thanks to Tony Finch for the zone cut - algorithm in Appendix A. Thanks to Paul Vixie for pointing out that - there are practical advantages (besides privacy) to qname m12n. + Thanks to Olaf Kolkman for the original idea although the concept is + probably much older [1]. Thanks to Mark Andrews and Francis Dupont + for the interesting discussions. Thanks to Brian Dickson, Warren + Kumari and David Conrad for remarks and suggestions. Thanks to + Mohsen Souissi for proofreading. Thanks to Tony Finch for the zone + cut algorithm in Appendix A. Thanks to Paul Vixie for pointing out + that there are practical advantages (besides privacy) to qname m10n. Thanks to Phillip Hallam-Baker for the fallback on A queries, to deal with broken servers. Thanks to Robert Edmonds for an interesting anti-pattern. 7. References 7.1. Normative References [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. - [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, July 2013. - [I-D.bortzmeyer-dnsop-dns-privacy] - Bortzmeyer, S., "DNS privacy considerations", draft- - bortzmeyer-dnsop-dns-privacy-02 (work in progress), April - 2014. + [I-D.ietf-dprive-problem-statement] + Bortzmeyer, S., "DNS privacy considerations", draft-ietf- + dprive-problem-statement-01 (work in progress), January + 2015. 7.2. Informative References [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. - [dprive] IETF, , "The DPRIVE working group of IETF", March 2014, - . + [I-D.wkumari-dnsop-hammer] + Kumari, W., Arends, R., Woolf, S., and D. Migault, "Highly + Automated Method for Maintaining Expiring Records", draft- + wkumari-dnsop-hammer-01 (work in progress), July 2014. + + [I-D.vixie-dnsext-resimprove] + Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS + Resolvers for Resiliency, Robustness, and Responsiveness", + draft-vixie-dnsext-resimprove-00 (work in progress), June + 2010. [dnsop] IETF, , "The DNSOP working group of IETF", March 2014, . + [mockapetris-history] + Mockapetris, P., "Private discussion", January 2015. + +7.3. URIs + + [1] https://lists.dns-oarc.net/pipermail/dns- + operations/2010-February/005003.html + Appendix A. An algorithm to find the zone cut Although a validating resolver already has the logic to find the zone cut, other resolvers may be interested by this algorithm to follow in order to locate this cut: (0) If the query can be answered from the cache, do so, otherwise iterate as follows: (1) Find closest enclosing NS RRset in your cache. The owner of