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IPv6 Operations                                                E. Vyncke
Internet-Draft                                                     Cisco
Intended status: Informational                          October 27, 2014
Expires: April 30, 2015

   Happy Eyeballs Considerations for HTTP State Management Mechanisms


   HTTP servers usually save session states in their persistent storage
   indexed by session cookies generated by the HTTP servers.  It is up
   to the HTTP user-agent to send this session cookie on each HTTP
   request.  Some HTTP servers check whether the cookie is associated
   with the HTTP user-agent by the means of the user-agent IP address...

   If the Happy Eyeball mechanism is used to select between IPv6 and
   IPv4, it may happen that while using the same HTTP server, some HTTP
   requests are done over IPv6 and the others over IPv4, which leads to
   two different sets of session states in the HTTP server.  This has
   the consequence of inconsistencies at the HTTP server.

   The only purpose of this document is to document this issue.

   A similar problem arises with the use of non RFC 6888 compliant Large
   Scale NAT (LSN) devices used to access an IPv4-only HTTP server.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 30, 2015.

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Copyright Notice

   Copyright (c) 2014 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  HTTP Session Management with HTTP Cookie  . . . . . . . . . .   2
   2.  Other Use of Session Cookies  . . . . . . . . . . . . . . . .   3
   3.  Happy Eyeballs Issue  . . . . . . . . . . . . . . . . . . . .   3
   4.  Large Scale NAT Issue . . . . . . . . . . . . . . . . . . . .   4
   5.  Potential Mitgation . . . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  HTTP Session Management with HTTP Cookie

   HTTP requests are basically stateless, therefore if a HTTP server
   requires to have some states associated to a HTTP user-agent (such as
   user name, login state, history, shopping basket, ...), there is a
   need to conserve those states.  This is usually done by using a HTTP
   cookie (see also [RFC6265]) identifying the session; also called
   "session state cookie".

   This session state cookie is generated by the HTTP server at the very
   first HTTP request from a HTTP user-agent.  The cookie is usually
   opaque (often a random number) and has no semantic except as being an
   index within the persistent storage of the HTTP server.  This index
   is used to access the complete state of the user-agent.  This
   mechanism is secure if the cookie is transferred with confidentiality
   between the server and the user-agent.  If the cookie transfer and
   storage are not secured, then any hostile user-agent can reuse this
   cookie to access the full original session states (including shopping
   basket, payment details, ...).

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   Some HTTP applications link the user-agent IP address (whether IPv6
   or IPv4) to the session state, probably for additional security
   checks in order to prevent session cookie stealing.  This link leads
   to some issues in a dual-stack world which are described in this

   The author knows about at least two large web sites having this
   problem.  It was so severe that those sites which were dual-stack had
   to move back to being IPv4-only... until the application and its
   security is updated.

2.  Other Use of Session Cookies

   Beside the use of session cookies by the HTTP server to keep states
   on the server, the very same cookie is also sometimes used by Server
   Load Balancing (SLB) mechanism to ensure that all HTTP requests from
   the same user-agent (even if behind a NAT) are always sent to the
   same physical HTTP server.  This is required if the server persistent
   storage is local to the server and is not shared by all the physical
   servers behind the SLB.

3.  Happy Eyeballs Issue

   When a HTTP user-agent uses the Happy Eyeball [RFC6555] mechanism to
   access a HTTP server, then, part of the HTTP requests can happen over
   IPv6 and another part over IPv4 if the latency between IPv4 and IPv6
   varies quickly over time.  If there is a link between the session
   cookie and the user-agent IP address, then upon the first change of
   IP protocol version, the states associated to the cookie will be
   invalidated and will be deleted.  Here is an example:

   1.  User-agent with IPv4 address, ADDR4, connect to the server by
       using IPv4 because IPv6 is slower; the first request does not
       have any HTTP cookie;

   2.  Server generates a new cookie C4 and stores in its persistent
       storage that C4 is associated with address ADDR4;

   3.  User-agent continues his/her session using IPv4, on each new
       request the HTTP server receives the cookie C4 and checks that
       the user-agent address is indeed ADDR4;

   4.  Latency of IPv6 changes and becomes now faster than IPv4;

   5.  User-agent now uses its IPv6 address, ADDR6, to connect to the
       same server and continues to use the same cookie C4 as the server
       name is unchanged;

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   6.  The server receives the HTTP request with the C4 cookie and
       checks whether C4 is associated with ADDR6 which is not the
       case...  All session states are deleted and a new cookie, C6, is
       generated and associated to the IPV6 address ADDR6;

   7.  The end-user becomes frustrated because he/she has to restart
       his/her complete session from the beginning.

   This cookie invalidation may have some security benefit but it
   actually prevents a host using Happy Eyeballs to have a persistent
   session with a dual-stack HTTP server; with painful consequences for
   the user-experience: disconnection, loss of shopping basket, ...

4.  Large Scale NAT Issue

   [RFC6888] describes the LSN requirements but not all LSN implement
   them.  Some LSN in the real world have a pool of IPv4 addresses and
   do not always use the same public IPv4 address for all requests from
   a LSN client.  This obviously leads to the same problem as in section
   Section 3.  Whether the LSN is used by IPv4 clients or by IPv6
   clients does not make any difference to the problem.

5.  Potential Mitgation

   A potential mitigation for this issue is NOT to link any HTTP state
   management (including cookies) to any IP address of the HTTP user-

6.  IANA Considerations

   This document contains no IANA considerations.

7.  Security Considerations

   The association of the session cookie with the user-agent IP address
   has some security value as it effectively prevents "session cookie
   stealing"; this benefit should be balanced with the lack of
   persistent session and the remaining vulnerability if the HTTP
   session can be intercepted by a man-in-the-middle attack.

8.  Acknowledgements

   The author would like to thank Dan Wing and Andrew Yourtchenko for
   some discussions on this topic.

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9.  Informative References

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, April 2012.

   [RFC6888]  Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common Requirements for Carrier-Grade NATs
              (CGNs)", BCP 127, RFC 6888, April 2013.

Author's Address

   Eric Vyncke
   De Kleetlaan 6a
   Diegem  1831

   Phone: +32 2 778 4677
   Email: evyncke@cisco.com

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