Network Working Group                                       T. Henderson
Internet-Draft                                        The Boeing Company
Expires: August 14, 2005                               February 13, 2005

                   Using HIP with Legacy Applications

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on August 14, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   The Host Identity Protocol and architecture (HIP) proposes to add a
   cryptographic name space for network stack names.  From an
   application viewpoint, HIP-enabled systems support a new address
   family (e.g., AF_HOST), but it may be a long time until such
   HIP-aware applications are widely deployed even if host systems are
   upgraded.  This informational document discusses implementation and
   API issues relating to using HIP in situations in which the system is

Henderson               Expires August 14, 2005                 [Page 1]

Internet-Draft     Using HIP with Legacy Applications      February 2005

   HIP-aware but the applications are not.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Approaches for supporting legacy applications  . . . . . . . .  5
     3.1   Using IP addresses in applications . . . . . . . . . . . .  5
     3.2   Using DNS  . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.3   Connecting directly to a HIT . . . . . . . . . . . . . . .  7
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  8
       Intellectual Property and Copyright Statements . . . . . . . .  9

Henderson               Expires August 14, 2005                 [Page 2]

Internet-Draft     Using HIP with Legacy Applications      February 2005

1.  Introduction

   The Host Identity Protocol (HIP) [1] is an experimental effort in the
   IETF and IRTF to study a new public-key-based name space for use as
   host identifiers in Internet protocols.  Fully deployed, the HIP
   architecture will permit applications to explicitly request the
   system to connect to another named host by expressing the name of the
   host when the system call to connect is performed.  However, there
   will be a transition period during which systems become HIP-enabled
   but applications are not.

   When applications and systems are both HIP-aware, the coordination
   between the application and the system can be straightforward.  For
   example, using the terminology of the widely used sockets API, the
   application can issue a system call to connect to another host by
   naming it explicitly, and the system can perform the necessary
   name-to-address mapping to assign appropriate routable addresses to
   the packets.  To enable this, a new address family (e.g., AF_HOST)
   could be defined, and additional API extensions could be defined
   (such as allowing IP addresses to be passed in the system call, along
   with the host name, as hints of where to initially try to reach the

   This draft does not define a native HIP API such as described above.
   Rather, this draft is concerned with the scenario in which the
   application is not HIP-aware and a traditional (sockets) API is used
   by the application.  To use HIP in such a situation, there are a few
   basic possibilities:  i) allow applications to use IP addresses as
   before, and provide a mapping from IP address to host name (and back
   to IP address) within the system, ii) take advantage of domain name
   resolution to provide the application with either an alias for the
   host identifier or (in the case of IPv6) the host identity tag (HIT)
   itself, and iii) support the use of HITs directly (without prior DNS
   resolution) in place of IPv6 addresses.  This draft describes several
   variations of the above strategies and suggests some pros and cons to
   each approach.

Henderson               Expires August 14, 2005                 [Page 3]

Internet-Draft     Using HIP with Legacy Applications      February 2005

2.  Terminology

   Referral:  When the application passes what it believes to be an IP
      address to another application instance on another host, within
      its application data stream.  An example is the FTP PORT command.

   Resolver: The system function used by applications to resolve domain
      names to IP addresses.

Henderson               Expires August 14, 2005                 [Page 4]

Internet-Draft     Using HIP with Legacy Applications      February 2005

3.  Approaches for supporting legacy applications

   This section provides examples of how legacy applications, using
   legacy APIs, can operate over a HIP-enabled system and use HIP.  The
   examples are organized by the name used by an application (or
   application user) to name the peer system:  an IP address, a domain
   name, or a HIT.

3.1  Using IP addresses in applications

   Consider the case in which an application issues a "connect(ip)"
   system call to connect to a system named by address "ip", but for
   which we would like to enable HIP to protect the communications.
   Since the application or user does not (can not) in this case
   indicate a desire to use HIP by using the standard sockets API, the
   decision to invoke HIP must be done on the basis of policy.  For
   example, if an IPsec-like implementation of HIP is being used, a
   policy may be entered into the security policy database that mandates
   to use or try HIP based on a match on the source or destination IP
   address, or other factors.

   There are a number of ways that HIP could be used in such a scenario.

   Manual configuration:
      Pre-existing SAs may be available due to previous administrative

      The system could send an I1 to the Responder with an empty value
      for Responder HIT.

   Using DNS:
      If the responder has host identities registered in the forward DNS
      zone and has a PTR record in the reverse zone, the initiating
      system could perform a reverse+forward lookup to learn the HIT
      associated with the address.

   These types of solutions have the benefit of naturally supporting
   application-level referrals, since the applications always use IP
   addresses.  They have weaker security properties than full HIP,
   however, because the binding between host identity and address is
   weak.  In fact, the semantics of the application's "connect(ip)" call
   may be interpreted as "connect me to the system reachable at IP
   address ip" but perhaps no stronger semantics than that.  HIP can be
   used in this case to provide perfect forward secrecy and
   authentication, but not to strongly authenticate the peer at the
   onset of communications.  DNS, if trusted, may be able to provide
   some additional initial authentication, but at a cost of initial

Henderson               Expires August 14, 2005                 [Page 5]

Internet-Draft     Using HIP with Legacy Applications      February 2005

   resolution latency.

3.2  Using DNS

   In the previous section, it was pointed out that a HIP-enabled system
   might make use of DNS to transparently fetch host identifiers prior
   to the onset of communication.  For applications that make use of
   DNS, the name resolution process is another opportunity to use HIP.
   If host identities are bound to domain names, with a trusted DNS, the
   following are possible:

   Return HIP LSIs instead of IP addresses:
      The system resolver could be configured to return a Local Scope
      Identifier (LSI) rather than an IP address, if HIP information is
      available in the DNS that binds a particular domain name to a host
      identity, and to otherwise return an IP address.  The system can
      then maintain a mapping between LSI and host identity and perform
      the appropriate conversion in the transport layer and below.  The
      application uses the LSI as it would an IP address.

   Locally use a HIP-specific domain name suffix:
      One drawback to spoofing the DNS resolution is that some
      applications actually may want to fetch IP addresses (e.g.,
      diagnostic applications such as ping).  One way to provide finer
      granularity on whether the resolver returns an IP address or an
      LSI is to distinguish by the presence of a domain name suffix.
      Specifically, if the application requests to resolve
      "" (or some similar suffix), then the system
      returns an LSI, while if the application requests to resolve
      "", IP address(es) are returned as usual.

   If the LSI is non-routable, a couple of potential hazards arise.
   First, applications that perform referrals may pass the LSI to
   another system that has no system context to resolve the LSI back to
   a host identity or an IP address.  Note that these are the same type
   of applications that will likely break if used over certain types of
   NATs.  Second, applications may cache the results of DNS queries for
   a long time, and it may be hard for a HIP system to determine when to
   perform garbage collection on the LSI bindings.

   It may be possible for an LSI to be routable, but such a case may not
   have the level of security in the binding to host identity that a HIT
   has with the host identity.  For example, a special IP address that
   have some location invariance is the identifier-address discussed in
   [2].  In general, LSIs considered to date for HIP have been

Henderson               Expires August 14, 2005                 [Page 6]

Internet-Draft     Using HIP with Legacy Applications      February 2005

3.3  Connecting directly to a HIT

   The previous two sections describe the use of IP addresses and and
   LSIs as "handles" to a host identity.  A third approach, for IPv6
   applications, is to configure the application to connect directly to
   a HIT (e.g., "connect(HIT)" as a socket call).  Although more
   cumbersome for human users (due to the flat HIT name space) than
   using either IPv6 addresses or domain names, this scenario has
   stronger security semantics, because the application is asking the
   system to connect specifically to the named peer system.

   It may be hard in this case for a system to distinguish between a HIT
   and a routable IPv6 address.  Elsewhere it has been proposed that
   HITs be precluded (temporarily) from using highest-ordered bits that
   correspond to IPv6 addresses, so that at least in the near term, a
   system could differentiate between a HIT and an IPv6 address by

   Another challenge with this approach is in actually finding the IP
   addresses to use, based on the HIT.  Some type of HIT resolution
   service would be needed in this case.

   A third challenge of this approach is in supporting referrals to
   possibly non-HIP-aware hosts.  However, since most communications in
   this case would likely be to other HIP-aware hosts (else the initial
   connect() would fail), the problem may be instead if the peer host
   supports HIP but is not able to perform HIT resolution for some

Henderson               Expires August 14, 2005                 [Page 7]

Internet-Draft     Using HIP with Legacy Applications      February 2005

4.  Security Considerations

   To be completed.

5  References

   [1]  Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-01
        (work in progress), October 2004.

   [2]  Nordmark, E. and M. Bagnulo, "Multihoming L3 Shim Approach",
        draft-ietf-multi6-l3shim-00 (work in progress), January 2005.

Author's Address

   Tom Henderson
   The Boeing Company
   P.O. Box 3707
   Seattle, WA


Henderson               Expires August 14, 2005                 [Page 8]

Internet-Draft     Using HIP with Legacy Applications      February 2005

Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at

Disclaimer of Validity

   This document and the information contained herein are provided on an

Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

Henderson               Expires August 14, 2005                 [Page 9]