One document matched: draft-barwood-dnsext-edns-page-option-01.txt

Differences from draft-barwood-dnsext-edns-page-option-00.txt

DNS Extensions Working Group                                  G. Barwood
Internet-Draft                                                           
Intended status: Standards track                          18 August 2009
Expires: February 2010


                           EDNS Page Option    
               draft-barwood-dnsext-edns-page-option-01    

Status of this Memo
   
   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   This Internet-Draft will expire on February 16, 2010.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
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   Please review these documents carefully, as they describe your rights
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Abstract

   Describes an EDNS option to allow large DNS responses to be sent 
   using small UDP packets.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . .  3

     2.1 Initial request  . . . . . . . . . . . . . . . . . . . . . .  3

     2.2 Server response  . . . . . . . . . . . . . . . . . . . . . .  4

     2.3 Follow-up request  . . . . . . . . . . . . . . . . . . . . .  4    

   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5

   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5

   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  5

   6.  Informative References . . . . . . . . . . . . . . . . . . . .  5



































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1.  Introduction

   DNSSEC implies that DNS responses may be large, possibly larger
   than the de factor ~1500 byte internet MTU.

   Large UDP packets are undesirable for 3 reasons:

   (1) Although the IP protocol specifies a means by which large IP 
   packets are split into fragments and then re-assembled, in practice
   this mechanism cannot be relied on, and large UDP packets may fail
   to be delivered

   (2) If a single fragment is lost, the the entire response must be
   re-sent.

   (3) The large ratio between the request size and the response size
   allows malicious programs to mount "amplification" attacks.

   (4) Re-assembling fragments requires buffer resources, which opens
   up denial of service attacks.

   Instead, it is possible to use TCP, but this is undesirable, as TCP
   imposes significant overhead and state that is vulnerable to denial
   of service attack.

   Nearly all current DNS traffic is carried by UDP with a maximum 
   size of 512 bytes, and relying on TCP is a risk for the deployment
   of DNSSEC.

   A particular problem occurs with home router proxies, which
   often truncate DNS responses at 512 bytes. In this case, TCP does
   not help, and it is impossible to retrieve responses through the
   proxy.

   Therefore an EDNS option to allow large DNS responses to be sent 
   using small UDP packets is proposed.

   The option includes an authentication mechanism that prevents blind
   spoofing of the response, provided IP fragmentation does not occur.
   
2. Protocol

2.1 Initial request

   The client signals support in it's initial request by including
   an EDNS Page option containing the following data:

   - Secret Key ( 4 bytes )  

   The secret key is used to validate the response, preventing blind 
   spoofing.



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2.2 Server response   

   The server responds with an EDNS Page option containing the following
   option data:

   - Secret key ( 4 bytes )
   - Page size ( 2 bytes )
   - Page number ( 1 byte )
   - Cookie ( 4 bytes )
   - Total response size ( 2 bytes )
   - Page data
 
   The original Question is not sent.

   The secret key is a copy of the secret key sent in the request.

   The page size is chosen so that the complete response packet size
   does not exceed the EDNS UDP payload size as defined in [RFC2181]. 
   Servers may also limit the response size for other reasons, for 
   example to mitigate an amplification attack, or to avoid IP 
   fragmentation.

   The client allocates an assembly buffer, and copies the Page data
   into it, at offset (Page number) x (Page Size).

2.3 Follow-up request
  
   The client then sends a follow-up request for each page it has not
   yet received. Each follow-up request has the Question and an EDNS 
   page option with option data as follows:

   - Secret Key ( 4 bytes )
   - Page size ( 2 bytes )
   - Page number ( 1 byte )
   - Cookie ( 4 bytes )

   The cookie (possibly in conjunction with the Question) identifies a
   read-only representation of the full response on the server.

   The cookie has a lifetime of 5 seconds. After this time has elapsed,
   a SERVERFAIL error response may be generated.
   
   When the client has received all of the pages, the complete assembled
   response is then processed normally.

   The follow-up requests may be sent in parallel. The client should
   retry a request if no response is received after a timeout period.







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3.  Security Considerations

   The secret key may expose internal state to an attacker who controls
   a name server. It is essential that a cryptographically strong source
   of random numbers be used to generate the secret key. This must be 
   seeded from data that cannot be guessed by an attacker, such as
   thermal noise or other random physical fluctuations.

   Clients must verify the secret key in each response.

   Fragmented responses are vulnerable to blind spoofing, therefore
   fragmented responses should be avoided if possible.

4.  IANA Considerations

   The EDNS TYPE code for Page Option.  

5.  Acknowledgments


6.  Informative References

   [RFC2181]  P. Vixie, "Extension Mechanisms for DNS (EDNS0)", 
              RFC 2181, August 1999.

Author's Address

   George Barwood
   33 Sandpiper Close
   Gloucester 
   GL2 4LZ
   United Kingdom

   Phone: +44 452 722670
   EMail: george.barwood@blueyonder.co.uk




















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