DNS Operations(dnsop) K.F. Fujiwara
Internet-Draft JPRS
Intended status: Informational July 16, 2013
Expires: January 17, 2014
Side effect of DNSSEC: an increase of DS queries
draft-fujiwara-dnsop-ds-query-increase-01.txt
Abstract
An increase of periodic DS queries is observed at top level domain
(TLD) DNS servers. Almost all of periodic DS queries are queries for
unsigned delegations. The reason of the increase is low NCACHE TTL
value and DS nonexistence. This phenomena is DNSSEC protocol and DNS
parameter issue. DS queries will increase as DNSSEC validators will
increase.
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document authors. All rights reserved.
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Internet-Draft Increase of DS queries July 2013
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Table of Contents
1. Problem statement . . . . . . . . . . . . . . . . . . . . . . 2
2. Possible affected domain names . . . . . . . . . . . . . . . 3
3. Possible solutions . . . . . . . . . . . . . . . . . . . . . 3
4. Possible approaches . . . . . . . . . . . . . . . . . . . . . 4
5. Issues of Dummy DS . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Problem statement
Many TLDs have supported DNSSEC. However, many delegations do not
have DS resource records. Some of full-resolvers support DNSSEC
validation.
A significant increase of DS queries is observed at JP TLD DNS
servers. 3.7% of queries are DS queries at JP TLD DNS servers in
July, 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 conditions of this phenomena 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
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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 for TLD DNS servers one zone cut per
NCACHE TTL seconds.
JP TLD case, NS, DS 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 receives 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.
2. 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).
3. Possible solutions
There are four approaches to the problem.
1. Lengthen NCACHE TTL value. However, this approach can not stop
the increase of DS queries because 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.)
2. Sign all delegations. If all delegations are signed, DS RR are
cached. However, a TLD can not control.
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3. Lengthen resource record TTL of popular names. However, a TLD
can not control.
4. Add dummy DS to unsigned delegations. Dummy DS RR is ignored at
DNSSEC validators and it indicates that the delegation is an
unsigned delegation. Dummy DS TTL value is controllable. This
proposal requires new digest type. Issues of this proposal is
discussed in Section 5.
5. Update DNS/DNSSEC protocol to reduce unnecessary DS queries.
4. Possible approaches
A TLD can control its NCACHE TTL value and its zone. Possible
approaches for A TLD are to prepare the increase, careful query
analysis, a combination of option 1 and option 4. Step by step
approach is possible.
1. Start discussing approaches (new digest type).
2. Prepare wide connectivity and reinforce DNS servers' performance.
3. Careful query analysis.
4. If DS queries will increase and exceed a certain limit, control
NCACHE TTL value.
5. If DS queries will increase and exceed a certain limit, add dummy
DS RRs to popular unsigned domain names.
5. Issues of Dummy DS
Adding dummy DS RRs to unsigned delegations is one of possible idea
to reduce unnecessary DS queries.
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 issues.
o TLD can not use opt-out technique defined in NSEC3 [RFC5155].
o Dummy DS RRs may be treated as a DNSSEC error.
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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.
6. Normative 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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