Internet DRAFT - draft-fujiwara-dnsop-ds-query-increase
draft-fujiwara-dnsop-ds-query-increase
DNS Operations(dnsop) K. Fujiwara
Internet-Draft JPRS
Intended status: Informational January 20, 2014
Expires: July 24, 2014
Side effect of DNSSEC: an increase of DS queries
draft-fujiwara-dnsop-ds-query-increase-02.txt
Abstract
An increase of periodic DS queries is observed at top level domain
(TLD) DNS servers. The reason of the increase is low NCACHE TTL
value and DS nonexistence. This memo presents issues with DNSSEC and
small NCACHE TTL value, including possible countermeasures in order
to prepare future increase of DS queries.
Status of This Memo
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This Internet-Draft will expire on July 24, 2014.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 2
3. Possible affected domain names . . . . . . . . . . . . . . . 3
4. Possible measures . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Dummy DS idea . . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
A significant increase of DS queries is observed at JP TLD DNS
servers. 4.5% of queries are DS queries at JP TLD DNS servers in
Dec., 2013 and they are still increasing. Almost all query names of
DS queries are unsigned zone cuts. These DS queries are useless for
DNSSEC validation because they are unsigned delegations. Very small
number of IP addresses send most of DS queries and the DS queries are
periodic. The reason of the increase is low NCACHE TTL value and DS
nonexistence. Details are described in Section 2. Possible affected
domain names are described in Section 3. Possible countermeasures
are described in Section 4.
2. Problem statement
Many TLDs have supported DNSSEC. However, many delegations do not
have DS resource records. Some of full-resolvers support DNSSEC
validation.
The conditions of the DS query increase are as follows.
o TLD's TTL value is relatively high, e.g., 86400.
o TLD's NCACHE TTL value is low, e.g., 900.
o There are many popular query names whose resource record TTLs are
low, e.g., 300, and they are unsigned.
o DNSSEC validators receive queries of popular names frequently,
e.g. every 5 minutes.
An unsigned delegation does not have a DS RR in its TLD zone. DNSSEC
validation process starts when the validator receives a query and it
does not exist in the validator's cache. DNSSEC validators need to
know DS RR existence for each query name. The DS RR nonexistence
information is cached within NCACHE TTL. As a result, each DNSSEC
validator may send DS queries to TLD DNS servers one zone cut per
NCACHE TTL seconds.
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This phenomena is DNSSEC protocol and DNS parameter issue. DS
queries will increase as DNSSEC validators will increase.
JP TLD case, NS and glue TTL is 86400 and NCACHE TTL is 900. There
are many popular names which are unsigned domain names and whose TTLs
are low. TTL of "www.yahoo.co.jp" A is 60 (CNAME TTL is 900 and TTL
of aliased name is 60) and TTL of "www.google.co.jp" A is 300. Busy
full-resolvers receive both queries every minutes or more. When a
busy full-resolver enables DNSSEC validation, it will send
"yahoo.co.jp" and "google.co.jp" DS queries every 900 seconds.
"yahoo.co.jp" NS and "google.co.jp" NS are cached in a day (86400
seconds). As a result, queries to JP DNS servers may increase 96
(86400 / 900) times at the maximum. This is DNSSEC protocol and
parameter issue.
3. Possible affected domain names
Possible affected domain names are delegation centric domain names
which support DNSSEC, whose NCACHE TTL is low, and which has popular
domain names which are not signed and use low TTL values.
TLDs: com, net, org, jp use 900 as NCACHE TTL value. Magnification
is 96 or more.
Reverse DNS: 193.in-addr.arpa uses 3600 as NCACHE TTL value.
Magnification is 48.
The root is affected a little because popular TLDs have already been
signed and the magnification is not high, 8 or 24 (86400 / 10800 or
86400 / 3600).
4. Possible measures
There are no good solutions and five possible measures to the
problem.
1. Reinforce DNS infrastructures.
2. Sign popular domain names. If popular domain names are signed,
their DS RRs are cached. However, a TLD can not control them.
Some TLDs have been trying to increase signed delegations by
price or security campaigns.
3. Lengthen resource record TTL of popular names. However, a TLD
can not control.
4. Lengthen NCACHE TTL value. However, the value is chosen by the
TLD's policy and this approach can not stop the increase of DS
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queries. Section 5 of DNS NCACHE [RFC2308] recommends negative
cache time limit as values of one to three hours. Lengthening
NCACHE TTL value over 10800 is useless. Magnification can only
be lowered. (JP case, from 96 to 8 or 24.)
5. Update DNS/DNSSEC protocol to reduce unnecessary DS queries.
There are some idea.
1. Changing validator's caching algorithms.
2. Adding dummy DS to popular unsigned delegations. Details are
described in Section 4.1.
Without protocol modifications, we need to reinforce DNS
infrastructures and try to increase signed delegations.
4.1. Dummy DS idea
"Adding dummy DS to popular unsigned delegations." Dummy DS RR may
be ignored by traditional DNSSEC validators and it indicates that the
delegation is an unsigned delegation. Dummy DS TTL value is
controllable. This proposal requires new digest type.
Dummy DS RR will be ignored by traditional DNSSEC validators because
Section 5.2 of DNSSEC Protocol [RFC4035] defines that the resolver
should treat unknown digest type as no DS RRset exists. BIND 9 and
Unbound validators ignored dummy DS RR whose digest type is 255.
However, there are many considerations.
o Dummy DS RRs may be treated as a DNSSEC error. Google public DNS
reports validation error at dummy DSs. BIND 9 and Unbound
validators ignore dummy DSs. DNSSEC Protocol [RFC4035] may be
ambiguous.
o Dummy DS RRs increase signing costs because most of TLDs use opt-
out technique defined in NSEC3 [RFC5155] to reduce signed domain
names.
o Newly added DS RRs may be used within dummy DSs' TTL seconds (for
example, it will be 1 day). Without dummy DS RRs, newly added DS
RRs are used within NCACHE TTL (900 or 10800 seconds).
o Is it allowed that TLDs add dummy DS RRs without registrants'
consent? If adding dummy DS is same as 'NO DS', it is possible.
Otherwise, TLDs cannot add dummy DS RRs without registrants'
consent.
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5. References
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008.
Author's Address
Kazunori Fujiwara
Japan Registry Services Co., Ltd.
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065
Japan
Phone: +81 3 5215 8451
EMail: fujiwara@jprs.co.jp
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