Internet DRAFT - draft-lee-dnsop-recursion-performance-improvement
draft-lee-dnsop-recursion-performance-improvement
Domain Name System Operations X. Lee
Internet-Draft H. Li
Intended status: Best Current Practice H. Zhang
Expires: May 4, 2016 P. Zuo
CNNIC
November 2015
An approach to improve recursion performance
draft-lee-dnsop-recursion-performance-improvement-00
Abstract
A recursive DNS server generally uses random port numbers to send
outbound requests to protect against DNS spoofing attacks. Due to
the limitation of operation system, a process typically can only open
numerable file descriptors simultaneously. This limit reduces
recursion performance of resolvers. This draft offers an approach to
improve both recursion performance and security for recursive
servers.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 4, 2016.
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to this document. Code Components extracted from this document must
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1. Introduction
A recursive DNS server generally uses random port numbers to send
outbound requests to avoid cache poisoning. This is also essential
to protect against Dan Kaminsky's DNS attack. Due to the limitation
of operation system, a process typically can only open numerable file
descriptors simultaneously. For example, the limitation on Linux is
1024 by default. Although this configuration could be modified by
operation system operators, there is still a limit for maximum port
number (65535).This limitation not only reduces recursion
performance, but also makes resolvers vulnerable to attackers.
Suppose that a hacker sends thousands of queries for domains which
change irregularly and are actually not exist, the resolver must
start corresponding recursive requests to authoritative servers as
these domains are not cached, and soon, this resolver will not be
able to generate more outbound requests because no more file
descriptor can be open.
This draft proposes an approach to solve this problem. A resolver
should reuse a group of fixed port numbers for outbound requests. In
this case, the resolver could improve recursion performance greatly
as it avoids limitation of maximum file descriptors. As for
security, the resolver should add an extra recursive identifier(RQID)
in EDNS0 record in outbound requests. Authoritative servers should
copy this RQID in EDNS0 record to the response packet. The resolver
then match up the reply using RQID option. In this case, this
approach improves security because a hacker can hardly correctly
guess the randomized 32bit RQID besides the Transaction ID in DNS
message header.
2. Protocol changes
This draft uses an EDNS0 ([RFC6891]) option to include recursive
query ID(RQID) in DNS messages. The option is structured as follows:
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+0 (MSB) +1 (LSB)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0: | OPTION-RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2: | OPTION-LENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
4: | |
+ (RQID)Recursive Query ID |
6: | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
o (Defined in [RFC6891]) OPTION-CODE, 2 octets, for RQID is 10.
o (Defined in [RFC6891]) OPTION-LENGTH, 2 octets, use 4 as
recommended.
o RQID, a 32 bit identifier(recommended) assigned by the resolver
that generates a recursive query. This RQID should be copied by
authoritative server to the corresponding reply message and then
be used by the resolver to match up the reply.
3. Stub Resolver Considerations
This approach is aimed to work between recursive servers and
authoritative servers, a stub resolver by itself should determine if
it has to support this RQID option.
4. Recursive Server Considerations
A resolver supporting RQID option should reuse fixed port numbers to
send recursive queries to improve performance. The port number could
be configured by users and the RQID function should also be
configurable.
If the RQID function is enabled, a resolver should behave as follows:
When sending a query, it generates a random 32 bit RQID (recommended)
in the EDNS0 record as described above. This RQID option indicates
the resolver reuses its port to send recursive queries and expect the
authoritative server to copy the RQID option in the responses. When
receiving a response, it should check RQID option in EDNS0 record in
the response to match up the reply. If the response contains no
EDNS0 record or RQID option, the resolver itself should determine if
to accept this reply. For compatibility, it is recommended to accept
these replies. This could increase the risk of cache poisoning, but
in most cases, the resolver should be secured by other
equipments(firewalls etc).
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If a recursive server receives a query containing RQID option from
stub resolver, it should copy this option in the reply.
5. Authoritative Server Considerations
If an authoritative server does not support RQID function, it just
ignores RQID option in EDNS0 record.
If a authoritative server supports RQID function, it should copy the
RQID option in the reply.
6. Performance Considerations
The recursive query performance should be greatly improved as the
resolver reuses port numbers to avoid the operation system limit of
maximum file descriptors.
7. Security Considerations
This draft proposes an approach to use a RQID(32 bit as recommended)
option to match up DNS replies. If both the recursive and
authoritative server support this option, the risk of cache poisoning
is much lower than previous protocol.
For compatibility, it is recommended to accept DNS replies which
contain no RQID option.
8. IANA Considerations
IANA is requested to assign the option code 10 for the RQID Option
Code in the EDNS0 meta-RR.
9. References
[RFC1035] Mockapetris, P., ""DOMAIN NAMES - IMPLEMENTATION AND
SPECIFICATION"", November 1987,
<http://www.rfc-editor.org/info/rfc1035>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, ""Extension Mechanisms
for DNS (EDNS(0))"", April 2013,
<http://www.rfc-editor.org/info/rfc6891>.
Authors' Addresses
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Xiaodong Lee
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3020
Email: lee@cnnic.cn
Hongtao Li
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3164
Email: lihongtao@cnnic.cn
Haikuo Zhang
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3163
Email: zhanghaikuo@cnnic.cn
Peng Zuo
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 2629
Email: zuopeng@cnnic.cn
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