Returning multiple answers in DNS responses.
draft-wkumari-dnsop-multiple-responses-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
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|---|---|---|---|
| Authors | Warren "Ace" Kumari , Zhiwei Yan , Wes Hardaker | ||
| Last updated | 2016-01-05 | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-wkumari-dnsop-multiple-responses-02
dnsop W. Kumari
Internet-Draft Google
Intended status: Standards Track Z. Yan
Expires: July 8, 2016 CNNIC
W. Hardaker
Parsons, Inc.
January 05, 2016
Returning multiple answers in DNS responses.
draft-wkumari-dnsop-multiple-responses-02
Abstract
This document (re)introduces the ability to provide multiple answers
in a DNS response.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 8, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Returning multiple answers . . . . . . . . . . . . . . . . . 3
5. Additional records pseudo-RR . . . . . . . . . . . . . . . . 5
5.1. File Format . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Wire Format . . . . . . . . . . . . . . . . . . . . . . . 5
6. Signaling support . . . . . . . . . . . . . . . . . . . . . . 6
7. Stub-Resolver Considerations . . . . . . . . . . . . . . . . 6
8. Use of Additional information . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
12.1. Normative References . . . . . . . . . . . . . . . . . . 7
12.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Often the name being resolved in the DNS provides information about
why the name is being resolved, allowing the nameserver to predict
what other answers the client will soon query for. By providing
multiple answers in the response, the authoritative name server
operator can ensure that the recursive server that the client is
using has all the answers in its cache.
For example, the name server operator of Example Widgets, Inc
(example.com) knows that the example.com web page at www.example.com
contains various other resources, including some images (served from
images.example.com), some Cascading Style Sheets (served from
css.example.com) and some JavaScript (data.example.com). A client
attempting to resolve www.example.com is very likely to be a web
browser rendering the page and so will need to also resolve all of
the other names to obtain these other resources. Providing all of
these answers in response to a query for www.example.com allows the
recursive server to populate its cache and have all of the answers
available when the client asks for them.
Other examples where this technique is useful include SMTP (including
the mail server address when serving the MX record), SRV (providing
the target information in addition to the SRV response) and TLSA
(providing any TLSA records associated with a name).
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This is purely an optimization - by providing all of other, related
answers that the client is likely to need along with the answer that
they requested, users get a better experience, iterative servers need
to perform less queries, authoritative servers have to answer fewer
queries, etc.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Background
The existing DNS specifications allow for additional information to
be included in the "additional" section of the DNS response, but in
order to defeat cache poisoning attacks most implementations either
ignore or don't trust additional information (other than for "glue").
For some more background, see [Ref.Bellovin], [RFC1034], [RFC2181].
Not trusting the information in the additional section was necessary
because there was no way to authenticate it. If you queried for
www.example.com and got back answers for www.invalid.com you couldn't
tell if these were actually from invalid.com or if an attacker was
trying to get bad information for invalid.com into your cache. In a
world of ubiquitous DNSSEC deployment [Ed note: By the time this
document is published, there *will* be ubiquitous DNSSEC :-) ] the
iterative server can validate the information and trust it.
3. Terminology
Additional records Additional records are records that the
authoritative nameserver has included in the Additional section.
Primary query A Primary query (or primary question) is a QNAME that
the name server operator would like to return additional answers
for.
Supporting information Supporting information is the DNSSEC RRSIGs
that prove the authenticity of the Additional records.
4. Returning multiple answers
The authoritative nameserver should include as many of the instructed
Additional records and Supporting information as will fit in the
response packet.
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In order to include Additional records in a response, certain
conditions need to be met. [Ed note: Some discussion on each rule is
below]
1. Additional records MUST only be included when the primary name
and each additional record are signed using DNSSEC "valid".
2. Additional records MUST only be served over TCP connections, or
when DNS Cookies [ToDo: Ref] are in use. This is to mitigate
Denial of Service reflection attacks.[1]
3. Additional records SHOULD be contained within the same zone as
the primary name[2], or MAY be additionally be contained within a
child zone for which the name server is authoritative for,
assuming all DNSSEC validation records required to validate the
child(ren) are included as well. Note that the DS record, and NS
and glue records for a child zone may be returned even when no
other additional data for the child will be included.
4. The DNSSEC supporting information necessary to perform validation
on the records must be included. I.E., the RRSIGs required to
validate the Additional record information must be included.
5. The authoritative nameserver SHOULD include as many of the
additional records as will fit in the response. Each Additional
record MUST have its matching Supporting information. Additional
records MUST be inserted in the order specified in the Additional
records list.
6. Operators SHOULD only include Additional answers that they expect
a client to actually need. [3]
[Ed note 1: The above MAY be troll bait. I'm not really sure if this
is a good idea or not - moving folk towards TCP is probably a good
idea, and this is somewhat of an optional record type. Then again,
special handing (TCP only) for a record would be unusual. Additional
records could cause responses to become really large, but there are
already enough large records that can be used for reflection attacks
that we can just give up on the whole "keep responses as small as
possible" ship. ]
[Ed note 2: This is poorly worded. I mumbled about bailiwick,
subdomains, etc but nothing I could come up with was better. Also,
is this rule actually needed? I *think* it would be bad for .com
servers to be able to include Additional records for
www.foo.bar.baz.example.com, but perhaps <handwave>public-suffix-
list?! This rule also makes it easier to decide what all DNSSEC
information is required.]
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[Ed note 3: This is not enforceable. ]
5. Additional records pseudo-RR
To allow the authoritative nameserver operator to configure the name
server with the additional records to serve when it receives a query
to a label, we introduce the Additional Resource Record (RR).
5.1. File Format
The format of the Additional RR is:
label ADD "label,type; label,type; label,type; ..."
For example, if the operator of example.com would like to also return
A record answers for images.example.com, css.html.example.com and
both an A and AAAA for data.example.com when queried for
www.example.com he would enter:
www ADD "images,A; css.html,A; data,A; data,AAA;"
The entries in the ADD list are ordered. An authoritative nameserver
SHOULD insert the records in the order listed when filling the
response packet. This is to allow the operator to express a
preference in case all the records to not fit. The TTL of the
records added to the Additional section are MUST be the same as if
queried directly.
In some cases the operator might not know what all additional records
clients need. For example, the owner of www.example.com may have
outsourced his DNS operations to a third party. DNS operators may be
able to mine their query logs, and see that, in a large majority of
cases, a recursive server asks for foo.example.com and then very soon
after asks for bar.example.com, and so may decide to optimize this by
opportunistically returning bar when queried for foo. This
functionality could also be included in the authoritative name server
software itself, but discussions of these re outside the scope of
this document.
5.2. Wire Format
The wire format of the Additional RR is the same as the wire format
for a TXT RR:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ TXT-DATA /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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Where TXT-DATA is one or more charter-strings.
The Additional RR has RR type TBD [RFC Editor: insert the IANA
assigned value and delete this note]
6. Signaling support
Iterative nameservers that support Additional records signal this by
setting the OPT record's PL ("plus") bit (bit NN [TBD: assigned by
IANA] in the EDNS0 extension header to 1.
7. Stub-Resolver Considerations
No modifications need to be made to stub-resolvers to get the
predominate benefit of this protocol, since the majority of the speed
gain will take place between the validating recursive resolver and
the authoritative name server. However, stub resolvers may wish to
query directly for the Additional RR if it wants to pre-query for
data that will likely be needed in the process of supporting its
application.
8. Use of Additional information
When receiving Additional information, an iterative server follows
certain rules:
1. Additional records MUST be validated before being used.
2. Additional records SHOULD be annotated in the cache as having
been received as Additional records.
3. Additional records SHOULD have lower priority in the cache than
answers received because they were requested. This is to help
evict Additional records from the cache first, and help stop
cache filling attacks.
4. Iterative servers MAY choose to ignore Additional records for any
reason, including CPU or cache space concerns, phase of the moon,
etc. It may choose to only accept all, some or none of the
Additional records.
9. IANA Considerations
This document contains the following IANA assignment requirements:
1. The PL bit discussed in Section 6 needs to be allocated.
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10. Security Considerations
Additional records will make DNS responses even larger than they are
currently, leading to more large records that can be used for DNS
reflection attacks. We mitigate this by only serving these over TCP.
A malicious authoritative server could include a large number of
Additional records (and associated DNSSEC information) and attempt to
DoS the recursive by making it do lots of DNSSEC validation. I don't
view this as a very serious threat (CPU for validation is cheap
compared to bandwidth), but we mitigate this by allowing the
iterative to ignore Additional records whenever it wants.
By requiring the ALL of the Additional records are signed, and all
necessary DNSSEC information for validation be included we avoid
cache poisoning (I hope :-))
11. Acknowledgements
The authors wish to thank some folk.
12. References
12.1. Normative References
[Ref.Bellovin]
Bellovin, S., "Using the Domain Name System for System
Break-Ins", 1995,
<https://www.cs.columbia.edu/~smb/papers/dnshack.pdf>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<http://www.rfc-editor.org/info/rfc2181>.
[RFC5395] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", RFC 5395, DOI 10.17487/RFC5395, November
2008, <http://www.rfc-editor.org/info/rfc5395>.
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12.2. Informative References
[I-D.ietf-sidr-iana-objects]
Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
progress), May 2011.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From -00 to -01.
o Nothing changed in the template!
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Zhiwei Yan
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing 100190
P. R. China
Email: yanzhiwei@cnnic.cn
Wes Hardaker
Parsons, Inc.
P.O. Box 382
Davis, CA 95617
US
Email: ietf@hardakers.net
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