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Network Working Group                                           D. Zhang
Internet-Draft                                                     X. Xu
Intended status: Informational               Huawei Technologies Co.,Ltd
Expires: September 10, 2012                                       J. Yao
                                                                   CNNIC
                                                                  Z. Cao
                                                            China Mobile
                                                           March 9, 2012


             Overview of HIP Proxy Scenarios and Solutions
                      draft-irtf-hiprg-proxies-05

Abstract

   A Host Identity Protocol (HIP) proxy is a host that holds the keying
   material, and participates in HIP-based communications, on behalf of
   one or more hosts.

   HIP proxies play an important role in the transition from the current
   Internet architecture to the HIP architecture.  A core objective of a
   HIP proxy is to facilitate the communication between legacy (or Non-
   HIP) hosts and HIP hosts while not modifying the host protocol
   stacks.  In this document, the legacy hosts served by proxies are
   referred to as Legacy Hosts (LHs).  Currently, various design
   solutions of HIP proxies have been proposed.  These solutions may be
   applicable in different working circumstances.  In this document,
   these solutions are investigated in detail to compare their
   effectiveness in different scenarios.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on September 10, 2012.

Copyright Notice



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   Copyright (c) 2012 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.







































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  HIP Proxies  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Essential Functionality of HIP Proxies . . . . . . . . . .  5
     3.2.  A Taxonomy of HIP Proxies  . . . . . . . . . . . . . . . .  6
     3.3.  DI Proxies . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  N-DI Proxies . . . . . . . . . . . . . . . . . . . . . . .  9
     3.5.  Distributed Implementation of DI Proxies . . . . . . . . .  9
       3.5.1.  Distributed DI-HIT Proxies . . . . . . . . . . . . . . 10
       3.5.2.  Distributed DI-NAT Proxies . . . . . . . . . . . . . . 10
       3.5.3.  Distributed DI-transparent Proxies . . . . . . . . . . 10
     3.6.  DI Proxies Supporting Communication Initiated by HIP
           hosts  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   4.  Issues with LBMs in Supporting LHs to Initiate
       Communication  . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  LBMs adopting Load Balancers . . . . . . . . . . . . . . . 12
       4.1.1.  Load Balancer Supporting DI Proxy Components . . . . . 13
       4.1.2.  Load Balancer Supporting N-DI Proxy Components . . . . 13
     4.2.  LBMs without Load Balancers  . . . . . . . . . . . . . . . 14
       4.2.1.  Issues Caused by Intercepting DNS Lookups  . . . . . . 14
       4.2.2.  Issues with LBMs in Capturing and Processing
               Replies from HIP hosts . . . . . . . . . . . . . . . . 15
   5.  Issues with LBMs that also Support HIP Hosts to Initiate
       Communication  . . . . . . . . . . . . . . . . . . . . . . . . 16
     5.1.  DNS Resource Records for LHs . . . . . . . . . . . . . . . 17
     5.2.  An Asymmetric Path Issue . . . . . . . . . . . . . . . . . 18
   6.  Issues with Dynamic Load Balancing . . . . . . . . . . . . . . 20
     6.1.  Operations of DI-HIT Proxies . . . . . . . . . . . . . . . 21
     6.2.  Operations of DI-NAT Proxies . . . . . . . . . . . . . . . 21
     6.3.  Operations of DI-Transparent Proxies . . . . . . . . . . . 21
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
     11.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24











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1.  Introduction

   The Host Identity Protocol (HIP) and its architecture propose an
   alternative to the dual use of IP addresses as "locators" (routing
   labels) and "identifiers" (endpoint, or host, identifiers).  It
   introduces a new host identifier layer between the network layer and
   the transport layer so as to comprehensively address the issues of
   mobility, multi-homing and net-layer security.  The Host Identities
   (HIs) of HIP enabled hosts are cryptographically verifiable.  When
   two HIP hosts initiate their communication, they need to perform a
   handshaking process to authenticate each other and distribute
   symmetric keys for securing subsequent packet exchanges.  A HIP host
   and a legacy host cannot communicate with each other directly by
   using HIP, since HIP is designed to communicate between HIP hosts.

   As core components of HIP deployment solutions, HIP proxies have
   attracted increasing attention from both industry and academia.  A
   HIP proxy is a middlebox located between a legacy host and a HIP
   enabled host.  With the assistance of a HIP proxy, a legacy host can
   communicate with its desired HIP host without updating its protocol
   stack.

   Currently, multiple research efforts are engaged in both design and
   performance assessment of HIP proxies.  In this document, we attempt
   to investigate several important alternatives and compare their
   effectiveness in different scenarios.  There has previously been a
   detailed discussion of HIP proxies in [SAL05].  This document can be
   regarded as a complement of that paper.  Some new topics (e.g., the
   asymmetric path issues occurred in the load-balancing mechanisms for
   HIP proxies and the necessity of extending the HIP RR for HIP
   proxies) are discussed in the document.  Theoretically, legacy hosts
   and the HIP hosts which the legacy hosts intend to communicate with
   can be located anywhere in the network.  However, in this document,
   without mentioning otherwise, it is assumed that legacy hosts are
   located within a private network and HIP hosts are located in the
   public network, since this is the most important scenario that HIP
   proxies are expected to support [SAL05].

   The remainder of this document is organized as follows.  Section 2
   lists the key terminology used in this document.  In section 3, the
   essential functions of HIP proxies are indicated, and a
   classification of HIP proxies is proposed to facilitate subsequent
   analysis.  In section 4, we analyze the issues that HIP proxies have
   to face in constructing a Load Balancing Mechanism (LBM) which
   facilitates communication initiated by LHs.  Section 5 analyzes the
   issues that HIP proxies in a LBM have to face if they also need to
   support communication initiated by HIP hosts.  In section 6, we
   investigate the issues that HIP proxies have to deal with in



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   supporting dynamic load balancing and redundancy.  Section 7 provides
   conclusions, and Section 8 notes that no requests of IANA are made.
   Section 9 is the security considerations.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   BEX: HIP Base Exchange, a two-party cryptographic protocol used to
   establish communications context between HIP enabled hosts.

   LHs: Legacy Hosts which are represented as HIP hosts by HIP proxies.

   DI Proxy: DNS lookup Inspecting Proxy, A HIP proxy which needs to
   inspect or modify DNS lookups between the hosts it serves and their
   DNS servers or resolvers so as to collect essential information for
   subsequent service.

   HA: HIP Association, an IP-layer communications context for two HIP
   enabled host generated during a BEX execution.

   LBM: Load Balancing Mechanism, a mechanism which is able to
   distribute workload across multiple compments to avoid overload on a
   single component and increase the availability of the whole system.

   N-DI proxy: Non-DNS lookup Inspecting Proxy, A HIP proxy which does
   not need to intercept DNS lookups between the hosts and DNS servers
   in order to perform HIP proxying correctly.


3.  HIP Proxies

3.1.  Essential Functionality of HIP Proxies

   A primary function of HIP proxies is to facilitate the communication
   between legacy (or Non-HIP) hosts and HIP hosts while not modifying
   the host protocol stacks.  In order to achieve this, a HIP proxy
   needs to intercept the packets transported between LHs and HIP hosts
   before they arrive at their destinations.  Upon capturing such a
   packet, a HIP proxy needs to transfer it into the format which can be
   recognized by the destination host.

   Assume a proxy intercepts a packet sent out by a LH.  If the packet
   is destined to a HIP host, the proxy first tries to find out whether
   there is an appropriate HIP association (HA) in its local database to



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   process the packet.  If the HA exists, the proxy then uses the key
   maintained in the HA to encrypt the payload in the packet, transmits
   the packet into the HIP compatible format, and transfers it to the
   HIP host.  However, if there is no proper HA found, the proxy needs
   to use the HI and HIT assigned to the LH to carry out a HIP Base
   Exchange (BEX) and generate a new HA with the HIP host.  The newly
   generated HA is then maintained in the local database.

   Similarly, when processing a packet from a HIP host, the proxy needs
   to find a proper HA and use the keying material in the HA to decrypt
   the packet, and thus the packet is transferred into an ordinary IP
   packet and forwarded to the legacy host.

3.2.  A Taxonomy of HIP Proxies

   In practice, there are various design alternatives for HIP proxies.
   To benefit the analysis, in this document HIP proxies are classified
   into DNS lookup Intercepting Proxies (DI proxies) and Non-DNS lookup
   Intercepting Proxies (N-DI proxies).  As indicated by the name, a DI
   proxy needs to intercept DNS lookups in order to correctly process
   the follow-up communication between LHs and HIP hosts, while N-DI
   proxies do not have to.

   Note that a DI proxy implementation may also be designed to cooperate
   with a resolution server other than DNS.  That is, the DI proxy is
   able to intercept the lookup between a host that the proxy serves and
   the resolution server to benefit the pacekt transforming job.
   However, currently DNS is the only resolution mechanism analyzed and
   extended to support HIP communication.  Hence, DNS is only resolution
   mechanism considered in this document.

   To avoid confusion, in the remainder of this document, the terms
   "lookup" and "answer" are used in specific ways.  A lookup refers to
   the entire process of translating a domain name for a legacy host.
   The answer of a lookup is the response from a resolution server which
   terminates the lookup.

3.3.  DI Proxies

   Usually, before a host communicates with a remote host, the legacy
   host needs to consult a DNS server for the IP address of its
   destination.  On this premise, a DI proxy can effectively identify
   the HIP hosts which legacy hosts MAY contact in near future by
   intercepting DNS lookups.

   In practice, it is common to deploy one or multiple DNS resolvers for
   a private network.  A host in the private network can thus send its
   queries to a resolver instead of communicating with authoritative DNS



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   servers directly.  If the resolver has not cached the requested RRs,
   it will try to collect them from authoritative DNS servers.  In a
   lookup process, a resolver MAY have to contact multiple authoritative
   DNS servers before it eventually gets the desired DNS RRs.

   On the occasions where a resolver is located outside a private
   network, a HIP proxy located at the border of the network can
   intercept the DNS queries from LHs and then use the FQDNs obtained
   from the queries to initiate a new DNS lookup to the resolver to
   inquire about the desired information (AAAA RRs, HIP RRs, and etc.).
   If the host that the legacy host intends to communicate with is HIP
   enabled, the DNS resolver will hand out a HIP RR associated with an
   AAAA RR to the proxy.  After maintaining the needed information
   (e.g., HITs, HIs, and IPs addresses of the HIP hosts) in the local
   database for future usage, the proxy returns an answer with an AAAA
   RR to the legacy host.

   When the resolver is located inside the private network, conditions
   are a little more complex.  If a proxy is deployed on the path
   between LHs and the resolver, it can operate the same as what is
   illustrated in the above paragraph.  The proxies which can be
   deployed in this way are introduced in the remainder of this sub-
   section.  However, if a proxy is located at the border of the network
   (i.e., between the resolver and authoritative DNS servers), the proxy
   has to intercept the DNS lookups between the resolver and
   authoritative DNS servers.  Because the resolver MAY have to contact
   multiple authoritative DNS servers to get a desired answer, for the
   purpose of efficiency, the proxy can only inspect the responses from
   DNS servers and find out DNS answers.  Because the answer of a DNS
   lookup does not contain any NS RR, it can be easily distinguished
   from the intermediate responses.  After identifying a DNS answer, a
   DI proxy can locate the DNS server maintaining the desired RRs from
   the packet header and identify the FQDN of the inquired host from the
   packet payload.  Then, the proxy initiates an independent lookup to
   the DNS server to check whether the host is HIP enabled.  If it is,
   the proxy maintains the information of the host for future usage and
   returns an answer with an AAAA RR to the resolver.

   Besides intercepting DNS lookups, some kinds of DI proxies also
   modify the contents of the AAAA RRs in the DNS answers for LHs to
   enhance the efficiency or deploying flexibility.  For instance,
   [RFC5338] indicates that a HIP proxy can return HITs rather than IP
   addresses in DNS answers to LHs.  Consequently, when sending data
   packets, LHs will use the those HITs as the destination addresses.
   The HIP proxy can then advertise a route of the HIT prefix to attract
   the packet for HIP hosts.  [PAT07] also proposes a solution in which
   a HIP proxy maintains an IP address pool.  When sending a DNS answer
   to a LH, the proxy selects an IP address from its pool and inserts it



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   within the answer.  The legacy host will regard this IP address as
   the IP address of the peer it intends to communicate with.  In the
   subsequent communication, when the host sends a packet for the remote
   HIP host, it will use the IP address assigned by the proxy as the
   destination address.  Therefore, the HIP proxy can intercept the
   packets for the HIP hosts by advertising the routes of the IP
   addresses in its pool.  In the remainder of this document, these two
   types of proxies are referred to as DI-HIT proxies and DI-NAT proxies
   respectively, and the DI proxies which do not modify the contents of
   DNS answers (i.e., return the IP addresses of HIP hosts in answers)
   are referred to as DI-transparent proxies.

   Compared with DI-HIT and DI-NAT proxies, DI-transparent proxies show
   their limitations in multiple ways.  For instance, in practice it is
   reasonable for a LH to publish the IP address of its proxy instead of
   its own IP address within its DNS AAAA RR so that the packets for the
   LH will be firstly forwarded to the proxy.  Therefore, when a LH
   served by a DI-transparent proxy attempts to communicate with two
   remote LHs served by a same HIP proxy, it is difficult for the host
   to distinguish one remote host from the other as they both use the
   same IP address.  In addition, DI-transparent proxies cannot work
   properly in the circumstance where HIP hosts renumber their IP
   addresses during the communication due to, e.g., mobility or re-
   homing.  For DI-HIT or DI-NAT proxies, these issues can be largely
   mitigated as the IP addresses of HIP hosts will never be used by DI-
   HIT or DI-NAT proxies to identify hosts.

   Moreover, it is difficult for DI-transparent proxies to advertise
   routing information to attract the packets transported between LHs
   and remote HIP hosts.  Consequently, they need to be deployed at the
   borders of private networks.  DI-HIT (or DI-NAT) proxies, however,
   can easily attract the packets for HIP hosts to themselves by
   advertising routes to them because the packets destined to HIP hosts
   use HITs (or the IP addresses selected from pools) as their
   destination addresses.  Hence, they can be flexibly deployed inside
   the networks.  Therefore, in private networks which resolvers are
   located inside, DI-HIT or DI-NAT proxies can be deployed on the path
   between the resolvers and LHs and reduce the overhead on the proxies
   imposed by intercepting DNS lookups.

   DNSSEC [RFC4035] is desigend to prevent attackers from tampering or
   forging DNS lookups between resolvers and DNS server.  This solution
   may affect the deployment of HIP proxies.  For instance, DI-HIT and
   DI-NAT proxies need to modify the contents of DNS answers, and thus
   they should be only deployed on the path between legacy hosts and
   their resolvers if DNSSEC is deployed.  Therefore, a DI-HIT proxy (or
   a DI-NAT proxy) cannot be deployed in the middle of DNSSEC-enabled
   resolvers and authoritative DNS servers.



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3.4.  N-DI Proxies

   Unlike DI proxies, an N-DI proxy does not need to intercept DNS
   lookups transported between LHs (or resolvers) and DNS servers.

   In [SAL05], it is indicated that an N-DI proxy can maintain a list of
   the information of the HIP hosts if the HIP hosts that LHs intend to
   contact are predictable.  After intercepting a packet from a LH, the
   proxy can ensure the packet is for a HIP host if the destination
   address of the packet is maintained in the list.

   In the circumstances where it is difficult to predict the HIP hosts
   that LHs intend to contact in advance, an N-DI proxy needs to consult
   DNS servers to find out whether the destination IP address of a
   packet is associated with a HIP host or a legacy host.  The
   information obtained from the DNS servers can be maintained within
   two lists.  One list is for the information of HIP hosts; the other
   is for the information of legacy hosts.  When intercepting a packet,
   the N-DI first compares the destination address of the packet against
   the addresses in the lists to find out whether the destination of the
   packet is HIP enabled.  If the address is not maintained in the
   lists, the proxy then has to consult resolution systems and maintains
   the information of the host which the packet is aimed for in the
   correspondent list, according to the answers from resolution systems.

3.5.  Distributed Implementation of DI Proxies

   As discussed above, DI proxies have to intercept the DNS lookup
   packets between legacy hosts and DNS servers in order to correctly
   transform the packets transported between LHs and HIP hosts.  This
   requires that a DI proxy be deployed on the boundary of the private
   network or on the path where LHs and the DNS resolver transport their
   lookup packets.  In the circumstance where DNSSEC is deployed, a DI
   proxy cannot even be deployed on the boundary of the private network
   either, if the proxy needs to modify DNS lookup packets.  Such
   inflexibility MAY be undesirable under certain circumstances.

   This section analyzes a distributed design option of DI proxies which
   improves the deployment flexibility of DI proxies and addresses the
   DNSSEC issue by deploying the DNS related functionality (i.e.,
   intercepting and modifying the DNS communication) and the packet
   transforming functionality on different components.  The component
   performing the DNS lookup interception is referred to as the DNS
   lookup inspector while the component performing the packet
   transformation is referred to as the proxy component.  A DNS lookup
   inspector is located in a place where it can intercept and modify DNS
   lookups.  In practice, a DNS resolver can also be extended to act as
   an inspector.



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3.5.1.  Distributed DI-HIT Proxies

   The DNS lookup inspector of a distributed DI-HIT proxy returns HITs
   in DNS answers to LHs.  Therefore, the associated DI-HIT proxy can
   advertise routing information inside the private network to attract
   the packets using HITs as destination addresses.  Additionally, the
   inspector needs to forward other information (e.g., IP addresses of
   the HIP hosts and RVSes) of the HIP hosts contained in DNS RRs to the
   DI-HIT proxy component so that the proxy can perform HIP base
   exchanges with the HIP hosts on behavior of LHs.

   A DI-HIT proxy component can work with multiple DNS lookup
   inspectors, and thus it is possible for a DI-HIT proxy component to
   be deployed in public networks to support multiple private networks.
   This property is useful when Internet services providers (ISPs)
   intend to facilitate the legacy hosts in the private networks without
   HIP proxies to communicate with HIP hosts.

   A DNS lookup inspector can also be associated with mutiple DI-HIT
   proxy components in order to distribute the traffic process overhead
   on different proxy components.  This deployment is discussed in
   Section 4 in details.

3.5.2.  Distributed DI-NAT Proxies

   A DNS lookup inspector of a distributed DI-NAT proxy needs to not
   only return the IP addresses in the address pool of the DI-NAT proxy
   component but also transfer the mapping information of the IP
   addresses and the correspondent HIP hosts to the DI-NAT proxy
   component.  Moreover, the resolver needs to maintain the mapping
   information so as to avoid assigning an IP address for multiple HIP
   hosts concurrently.

   Similar with Distributed DI-HIT Proxies, a DI-NAT proxy component can
   also be deployed in a public network.  In this case, the addresses in
   the address pool MUST be routable in the public network.  Moreover, a
   DNS lookup inspector can also be associated with mutiple DI-NAT proxy
   components in order to distribute the traffic process overhead on
   different proxy components.  This deployment is discussed in Section
   4 in details.

3.5.3.  Distributed DI-transparent Proxies

   A DNS lookup inspector of a distributed DI-transparent proxy does not
   need to modify DNS answers, but it needs to forward the IP addresses
   and HIs of queried HIP hosts to the DI-NAT proxy component.  In this
   case, a DI-transparent proxy component MUST be deployed on the
   boundary of the private network in order to guarantee that it can



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   intercept packets exchagne the local LHs and the remote HIP hosts.

3.6.  DI Proxies Supporting Communication Initiated by HIP hosts

   In the scenarios where HIP hosts initiate communication, the HIP-
   enabled host first launches the DNS query to retrieve the remote
   host's HI/HIT or RVS address.  Without knowing if the remote host
   supports HIP-based exchange, the HIP host is expecting to receiving
   the remote host HIP based Identities.


 +----------+                  +---------+               +-------------+
 | HIP Host |                  |  Proxy  |               | non-HIP host|
 +----------+                  +---------+               +-------------+
      | 1.DNS Query QTYPE=HIP       |                           |
      |---------------------------->|                           |
      | 2.DNS Response HIT&HI       |                           |
      |<----------------------------|                           |
      | 3.DNS Query QTYPE=A         |                           |
      |---------------------------->|                           |
      | 4.DNS Response IP-A         |                           |
      |<----------------------------|                           |
      | 5-8.                        |                           |
      | BASE EXCHANGE(I1,R1,I2,R2)  |                           |
      |<--------------------------->|                           |
      |                             |                           |
      |9.HIP PACKET FORMAT          | 10.  LEGACY IP PACKET     |
      |---------------------------->|-------------------------->|
      |                             |                           |
      |11.HIP PACKET FORMAT         | 12.  LEGACY IP PACKET     |
      |<----------------------------|<--------------------------|
      |                             |                           |
      |                             |                           |


                        Figure 1: Translation Proxy

   As shown in Figure 1 the proxy intercepts the DNS query and
   iteratively forward the query to the global DNS to find an answer.
   If the responder is HIP enabled, it will have its HI or HIT
   registered in the DNS and the proxy will get an answer.  However, if
   the responder is not HIP aware, and only has type A or AAAA records
   in the DNS system, the query for QTYPE=HIP will fail.  On detecting
   that the responder is not HIP aware, the DNS proxy will use a
   temporary HI/HIT (T-ID) generated locally and reply this temporary
   HI/HIT to the initiator.  The proxy will associate the T-ID with the
   IP address of the responder.  After the HIP RR query reponse, the
   Type-A query response is followed, via which the initiator get the



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   the IP address of the proxy node.

   The HIP base exchange will proceed between the initiator and the
   proxy (step.5-8).  Then, the HIP association is established between
   the initiator and the proxy, i.e., between the host's HI and the
   temporary HI assigned to the responder by the proxy.  If the
   initiator starts data communication towards the responder, the proxy
   on the data path will be responsible for the translation between HIP
   packets and IP packets.  First, the proxy will de-capsulate the
   packet and decrypt the packet to get the original IP packet inside.
   By inspecting the HIP header after the IP header, the proxy is aware
   of the destination's HIT/LSI.  If the HIT and LSI are mapped to one
   of the responder's IP addresses, the proxy will translate the packet
   with the destination address as the responder's IP address, and
   source address as the proxy IP address.  The destination port is kept
   unchanged, but the source port can be dynamically assigned.


4.  Issues with LBMs in Supporting LHs to Initiate Communication

   If there is only a single HIP proxy deployed for a private network,
   the proxy may become the cause of a single-point-of-failure.  In
   addition, when the number of the users increases, the overhead
   imposed on the proxy may overwhelm its capability, which makes the
   proxy a bottleneck of the whole mechanism.  A typical solution to
   mitigate this issue is to organize multiple proxies to construct a
   LBM.  By sharing overhead of processing packets amongst multiple HIP
   proxies, a LBM can be more scalable and fault tolerant.

4.1.  LBMs adopting Load Balancers

   Load balancers have been widely utilized in the design of LBMs.  When
   adopted in a HIP proxy LBM, a load balancer needs to pool all proxy
   resources and be located in a position where it can intercept DNS
   lookups or modify DNS lookups if necessary.  In addition, the load
   balancer needs to distribute the information it learned from the DNS
   lookups to the appropriate proxies it manages.  In some cases, the
   load balancer MAY also need to take the responsibility of forwarding
   the data packets to proper proxies.

   Logically, a LBM adopting Load balancer can be regarded as a
   variation of a distributed HIP Proxy.  A load balancer is an extended
   DNS lookup inspector that is able to distribute load to different DI
   proxy components according to pre-specified policies.  The policies
   adopted by different load balancers can be varied.  A load balancer
   may require that all the packets from a LH be processed by the same
   HIP proxy while other balancers may expect all the packets for a HIP
   host to be processed by the same HIP proxy.



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4.1.1.  Load Balancer Supporting DI Proxy Components

   In a LBM where a load balancer manages multiple DI-HIT proxy
   components, the load balancer MUST be able to intercept DNS lookup
   packets and forward the information about the HIP hosts being queried
   to the proxy components according to certain policies.  Additionally,
   the load balancer needs to modify DNS lookup packets and return HITs
   in DNS answers to LHs (or resolvers).  In order to intercept the
   packets sent from LHs to HIP hosts, the load balancer MAY need to
   advertise a route of the HIT prefix.  After intercepting a data
   packet from a LH, the balancer needs to forward the packet to the
   proxy component which can correctly process it.

   In a LBM where a load balancer manages multiple DI-NAT proxy
   components, the load balancer MUST be able to intercept and forward
   the information about the HIP hosts being queried to the appropriate
   proxy components.  Additionally, the load balancer needs to modify
   DNS answers and return IP addresses in the address pools of the
   assigned DI-NAT proxies in DNS answers to LHs (or resolvers).  DI-NAT
   proxies can advertise the routes of the IP addresses in the pools so
   that the load balancer does not have to intercept the packets between
   LHs and HIP hosts.

   In a LBM where a load balancer manages multiple DI-transparent proxy
   components, the load balancer MUST be able to intercept and forward
   the information about the HIP hosts being queried to the appropriate
   proxy components.  The load balancer does not modify DNS answers, but
   it needs to be located in a place (e.g., the egress of the private
   network) where it is able to intercept the packets sent from LHs to
   HIP hosts and forward them to the assigned proxies.

4.1.2.  Load Balancer Supporting N-DI Proxy Components

   When the HIP proxies that a load balancer manages are N-DI proxies,
   the load balancer does not intercept DNS lookups.  Instead, the load
   balancer MUST be located in a place (e.g., the egress of the private
   network) where it is able to intercept the packets sent to HIP hosts.
   When receiving a packet from a LH, the load balancer needs to decide
   the appropriate proxies which the pacekts should be forward to (e.g.,
   according to the prefix of the destination address of the packet).
   In this solution, because the load balancer does not forward the
   information about the HIP hosts being queried to the appropriate
   proxies, the N-DI proxy components need to consult resolution systems
   themselves.







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4.2.  LBMs without Load Balancers

   Generally, in a LBM without a load balancer, there are two methods to
   distribute communication between LHs and HIP hosts among different
   HIP proxies.  The first solution is to divide the LHs in the private
   network into different groups (e.g., according to their IP
   addresses), with the LHs in different sections served by different
   HIP proxies.  The second solution is to divide the HIP hosts in the
   Internet into multiple groups (e.g., according to their HITs or IP
   addresses); every HIP proxy serves all the LHs in the private network
   but only processes the packets to and from the HIP hosts in a group.
   Abstractly, the two solutions are identical.  However, the first
   solution requires a private network to be divided into multiple sub-
   networks, and each of them is served by a HIP proxy.  This may
   introduce additional modification to the topology of the private
   network, which is not desired in many cases.  Therefore, in the
   design of existing LBM solutions, the second type of solution can be
   more preferred.  In the remainder of this document, the second one is
   mainly discussed.

4.2.1.  Issues Caused by Intercepting DNS Lookups

   +--------------------+           +------------------+
   |                    |           |                  |
   |                +---+-------+   |                  |
   | +-----------+  |HIP proxy 1+---+      +---------+ |
   | |Legacy Host|  +---+-------+   |      |HIP Host | |
   | +-----------+      |     .     |      |  (HH1)  | |
   |                    |     .     |      +---------+ |
   |                +---+--------+  |                  |
   |                |HIP proxy n +--+                  |
   |Private Network +---+--------+  | Public Network   |
   |                    |           |                  |
   +--------------------+           +------------------+
   Figure 1: An example of LBM

   Figure 1 illustrates a simple LBM without a load balancer.  In this
   mechanism, n proxies are deployed at the border of a private network.
   If such proxies are DI-HIT proxies, in order to share the overhead of
   processing data packets, each proxy needs to advertise a route of the
   HIT section it takes responsibility for.  In addition, each proxy
   also needs to advertise a route of a section of IP addresses (or a
   default route for the entire IP address namespace) inside the private
   network to intercept DNS lookups.  A problem occurs when the DNS
   lookups and the data packets sent by a legacy host are intercepted by
   different proxies.  In such a case, the proxy intercepting a data
   packet will lack essential knowledge to correctly process it.  If the
   proxies adopted in Figure 1 are DI-transparent proxies, then each



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   proxy only needs to advertise a route of a section of IP addresses
   which is adopted to intercept both DNS lookups and data packets.  On
   this occasion, if a HIP host and the DNS server maintaining its RR
   fall into two different IP sections, the DI-transparent proxy
   intercepting the lookups for the HIP host will not be the one
   intercepting subsequent data packets.

   A candidate solution to the problem that DI-HIT-proxy-based LBMs and
   DI-transparent-proxy-based LBMs face is to propagate the mapping
   information obtained from DNS lookups amongst HIP proxies.
   Therefore, after intercepting a DNS conversation, a proxy can forward
   the learned information to the proxy expected to process the
   subsequent data packets.  Alternatively, a proxy can attempt to
   collect required information from resolution systems after
   intercepting a data packet.  This approach, however, imposes
   additional overhead for DI-proxies to consult resolution servers.

   If the proxies in Figure 1 are DI-NAT proxies, the problem is
   eliminated.  In a DI-NAT-proxy-based LBM, each DI-NAT proxy needs to
   advertise two routes: a route to one of the IP addresses in the pool
   and a route to one of a section of IP addresses for intercepting DNS
   lookups.  After intercepting a DNS lookup, a DI-NAT proxy will return
   an IP address within the pool in the answer to the requester (a LH or
   a resolver), which can ensure that subsequent data packets will be
   delivered to the same proxy.

   If a DNS resolver supporting DI proxies can forward the mapping
   information obtained from DNS lookups to appropriate HIP proxies, the
   issue can be easily addressed.  In this case, the DNS resolver
   actually acts as a load balancer.

4.2.2.  Issues with LBMs in Capturing and Processing Replies from HIP
        hosts

   Theoretically, when representing a LH to communicate with a HIP host
   in the public network, a HIP proxy can use either an IP address it
   possesses or the IP address of the LH as the source address of the
   packets forwarded to the HIP host.  However, in practice, the latter
   option may cause an asymmetric traffic issue in the load balancing
   scenarios where multiple HIP proxies provide services for the same
   group of LHs.  Assume there are two HIP proxies located at the border
   of a private network.  If the proxies adopt the latter solution, they
   need to advertise the routes of the LHs in the public network
   respectively.  As a result, it is difficult to guarantee the packets
   transported between a legacy host and a HIP host are bound to the
   same HIP proxy, and thus after a proxy intercepts a packet it may
   lack the proper HIP association to process it.




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   A possible solution to address this problem is to share HIP state
   information (e.g., HIP associations, sequence number of IPsec
   packets) amongst the related HIP proxies in a real-time fashion.
   However, during communication, some context information such as the
   sequence numbers of ESP packets can change very fast.  It is
   infeasible to synchronize the ESP message counters for every
   transmitted or received packet, since such operations will occupy
   large amounts of bandwidth and seriously affect the performance of
   HIP proxies.  [Nir 2009] indicates that this issue can be partially
   mitigated by synchronizing ESP message counters only at regular
   intervals, for instance, every 10,000 packets.

   An issue similar to the one mentioned above is discussed in [TSC05],
   and an extended HIP base exchange is proposed.  But the proposed
   solution only tries to help HIP-aware middleboxes obtain the SPIs
   generated in a HIP base exchange and cannot be directly used to
   address this problem.

   When adopting the preceding option, proxies need to advertise the
   routes to their addresses in the public network respectively, so that
   the packets transported between a LH and a HIP host are intercepted
   by the same proxy.  The issue discussed above can thus be addressed.
   In the following discussions, without mentioning otherwise we assume
   that a HIP proxy uses one of its IP addresses as the source IP
   addresses of the packets which it sends to a HIP host.


5.  Issues with LBMs that also Support HIP Hosts to Initiate
    Communication

   Apart from the basic functions (i.e., supporting LHs to initiate
   communication with HIP hosts), in many typical scenarios, HIP proxies
   MAY also need to facilitate the communication initiated by HIP hosts.
   In this section, we attempt to analyze the issues that a HIP proxy
   has to face in the case where HIP hosts proactively initiate
   communication with LHs.

   In order to support the communication initiated by HIP hosts, the HIP
   proxies of a private network should have the knowledge essential to
   represent its LHs to perform HIP base exchanges with remote HIP
   hosts.  Such knowledge consists of the IP addresses of the LHs in the
   private network, their pre-assigned HITs, the corresponding HI key
   pairs, and any other necessary information.  In addition, such
   information of the LHs should be advertised in resolution systems
   (e.g., DNS and DHT) as HIP hosts.  Otherwise, a HIP host has to
   obtain the HIT of the LH in the opportunistic model which, however,
   should only be adopted in secure environments.




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5.1.  DNS Resource Records for LHs

   In difference impelementations, the AAAA RR of a LH can consist of
   either the IP address of the LH or the address of its HIP proxy.  In
   the preceding approach, the routing infrastructure will try to
   forward the packets for the LH to the host directly.  Therefore, in
   this case, HIP proxies MUST be located on the path of such packets to
   intercept them.  In the latter approach, the packets for a legacy
   host are first forwarded to the associated HIP proxy.  Compared with
   the preceding approach, the latter approach enables a proxy to be
   deployed in a more flexible way.  In addition, this approach can be
   more efficient in the private networks where LHs and HIP hosts are
   deployed in an intermixed way, since the HIP proxy will not have to
   intercept the packets transported between HIP hosts.  However, the
   latter approach may cause problems when processing packets sent by
   legacy hosts in the public network.  Normally, a HIP proxy needs to
   serve a number of LHs.  When using the latter approach, the packets
   destined to these LHs will have a same destination address (i.e., the
   IP address of the proxy).  Therefore, when receiving a packet from a
   legacy host located in the public network, the proxy may find it
   difficult to identify the LH to which the packet should be forwarded.

   A simple approach which combines the advantages of the above two
   solutions but avoids their disadvantages is to extend the HIP RR
   [RFC5205] with a new proxy field, which contains the IP address of a
   HIP proxy.  In the extended HIP RR of a LH, the proxy field consists
   of the IP address of its HIP proxy, while the proxy field in the RR
   of an ordinary HIP host is left empty.  Therefore, a HIP host
   intending to communicate with the LH can obtain the IP address of the
   proxy from DNS servers and set it as the destination address of the
   packets.  The packets are then routed to the proxy.  When a non-HIP
   host intends to communicate with the legacy host, it can obtain the
   IP address of the legacy host from the AAAA RR as usual and set it as
   the destination address of the packets; the packets are then
   transported to legacy host directly.

   It is also possible to use the RVS field in a HIP RR to transport the
   information of a HIP proxy.  However, in certain scenarios, a special
   proxy field can bring additional security benefits.  For instance, it
   is normally assumed that the BEX protocol is able to establish a
   security channel for the hosts on the both sides of communication to
   securely exchange messages.  However, this presumption MAY be no
   longer valid in the presence of HIP proxies, as the messages between
   legacy hosts and proxies can be transported in plain text.  With the
   Proxy field, it is easy to distinguish the legacy hosts represented
   by HIP proxies from the ordinary HIP hosts.  Therefore, a HIP host
   can assess the risks of exchanging sensitive information with its
   communicating peers in a more precise way.



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5.2.  An Asymmetric Path Issue

   In a load balancing scenario where multiple HIP proxies are deployed
   at the border of a private network, the packets transported between a
   legacy host and a HIP host MAY be routed via different HIP proxies.
   Therefore, when a packet is intercepted by a HIP proxy, the proxy may
   find that it lacks essential knowledge to appropriately process the
   packet.  Hence, an asymmetric path issue occurs.

   In order to explain the asymmetric path issue in more detail, let us
   revisit the LBM illustrated in Figure 1.  In addition, assume that
   the HIP proxies are DI-HIT proxies and their IP addresses are
   maintained in the DNS RRs of the LHs.  When a HIP host (e.g., HH1)
   looks up a legacy host at a DNS server, the DNS server returns the IP
   addresses of all the HIP proxies in an answer (see Figure 2).  Upon
   receiving the answer, HH1 needs to select an IP address and sends an
   I1 packet to the associated HIP proxy.  Assume the HIP proxy 1 is
   selected.  Then after a base exchange, HIP proxy1 and HH1 establish a
   HIP association respectively.  Upon receiving the first data packet
   from HH1, the HIP proxy uses the HIP association to de-capsulate the
   packet and forward it to the legacy host.  In the forwarded packets,
   the HIT of HH1 is adopted as the source IP address, and thus the HIT
   of HHI is adopted as the destination address in the reply packets
   sent by the legacy host.  Assume that the HIT of HH1 is within the
   section managed by HIP proxy n.  According the routes advertised by
   the proxy n, the packet is forwarded to the HIP proxy n which,
   however, does not have the corresponding HIP association to deal with
   the packet.  Similarly with DI-HIT proxies, DI-transparent proxies
   and N-DI proxies also suffer from the asymmetric path issue in the
   load balancing scenarios, since they cannot guarantee the data
   packets which are transported between a legacy host and a HIP host
   stick to a single HIP proxy too.
   +----------------------+         +--------------------------+
   |                      |         |                          |
   |                  +---+-------+ | (3)                      |
   |            (4)  -|HIP proxy 1+-+<-                        |
   |                / +---+-------+ |  \ +--------+ (1)+------+|
   |+-----------+< -      |     .   |   -|HIP Host|--> |  DNS ||
   ||Legacy Host|-        |     .   |    |  (HH1) |<-- |Server||
   |+-----------+ \   +---+-------+ |    +--------+(2) +------+|
   |           (5) - >|HIP proxy n+-+                          |
   | Private Network  +---+-------+ |    Public Network        |
   |                      |         |                          |
   +----------------------+         +--------------------------+
   Figure 2. An example of the asymmetric path issue

   As we mentioned in section 3.3.1, the approach of synchronizing HIP
   associations and IPsec associations amongst HIP proxies can be used



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   to address this issue.  However, this issue will introduce additional
   communication overhead on HIP proxies.  Here, several alternative
   solutions are introduced as follows.

   The simplest solution is to allow a HIP proxy to discard the I1
   packets it receives if they are not originally from HIP hosts which
   the proxy covers.  In addition, the proxy can inform the senders of
   the incidents using ICMP packets.  Therefore, after waiting for a
   certain period or upon receiving a ICMP packet, a HIP host will try
   to select another HIP proxy from the list in the DNS answer and send
   an I1 packet to it.  In the worst case, this process needs to be
   recursive until all the HIP proxies in the list have been contacted.
   Because a HIP host may have to send the multiple I1 packets in order
   to communicate with a LH, this solution may yield a long delay.  Note
   that in some DNS based load balancing approaches, a DNS server only
   returns one HIP proxy in an answer.  On such occasions, HIP hosts
   have to communicate with DNS servers repeatedly, and the negative
   influence caused by the communication delay can be exacerbated.

   A solution which is able to avoid the delay issue is to endow DNS
   servers with the capability of returning the IP address of an
   appropriate HIP proxy in an answer according to certain policies (
   e.g., the HIT (if the proxy is a DI-HIT proxy or a N-DI proxy) or the
   IP address (if the proxy is a DI-transparent proxy) of a requester).
   That is, the HIP proxy described in a DNS answer should be able to
   correctly transform the packets exchanged between the requester and
   the LH that it intends to access.  In this case, DNS servers actually
   act as load balancers.  In order to support this solution, DNS
   servers need to be extended to 1) maintain the information about the
   sections of the namespaces that HIP proxies take in charge of and 2)
   locate the appropriate HIP proxy according to the HIT or the IP
   address of a HIP requester.  These requirements result in
   modifications to current DNS servers in terms of the implementation
   of the DNS server applications and the conversation protocols between
   requesters and DNS servers.  For instance, a HIP host may need to
   transport its HIT in DNS requests in order to help DNS servers locate
   an appropriate HIP proxy.  A negative impact of this solution is to
   introduce additional complexity and overhead to DNS servers.

   Another solution is to extend RVS servers as load balancers.  After
   receiving an I1 packet from a HIP host, the load balancer then
   selects a proper HIP proxy and forwards the packet to it.  Using this
   solution, a DNS server only needs to reply wiht a record upon
   receiving a query from a HIP host, which reduce the traffic
   transported between DNS servers and HIP hosts.

   The asymmetric path issue can be eliminated when DI-NAT proxies are
   adopted.  A DI-NAT proxy located at the border of a private network



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   maintains a pool of IP addresses which are routable in the private
   network.  After receiving a packet from a HIP host, the DI-NAT proxy
   processes the packet and forwards it to the destination legacy host.
   In addition, an IP address selected from the pool is adopted as the
   source address of the packet.  Therefore, when the legacy host sends
   response packets to the HIP host, the packets will be transported to
   the same HIP proxy.  The asymmetric path issue is thus eliminated.


6.  Issues with Dynamic Load Balancing

   In practice, there are requirements for LBMs to support dynamic load
   balancing.  That is, when the overhead imposed on a proxy surpasses a
   threshold, the proxy can delegate all of (or a part of) its job to
   other proxies.  A proxy providing backup service for another proxy is
   called a backup proxy, and the proxy being served is called a primary
   proxy.  Note that two proxies can be backup proxies for each other on
   different sessions.  In this section, we analyze the operations of
   different types of HIP proxies in supporting dynamic load balancing.

   In some LBMs adopting load balancers, when a load balancer detects
   that the overhead imposed on a proxy is high, it can flexibly
   distribute the load to other proxies.  However, in the LBMs where no
   load balancer is deployed, a backup proxy MUST be able to detect the
   abnormal condition of its primary proxy and take over the job.  A
   simple but effective solution to achieve this is to allow a backup
   proxy to advertise the routes identical to those advertised by the
   primary proxy in both the private and the public networks (but with
   high costs).  When the overhead is high, the primary proxy can
   withdraw the routes it previously advertised so that the packets
   supposed to be processed by the primary proxy will be forwarded to
   the backup proxy.  We refer to the routes advertised by a proxy for
   backup purposes as the backup routes of the proxy.  In contrast, we
   refer to the routes advertised by a proxy to conduct its primary job
   as the primary routes of the proxy.  Normally, the backup routes have
   much higher costs than those of the corresponding primary routes, in
   order to avoid affecting the normal operations of the primary proxy.
   Note that the proxies in a LBM can provide backup services for one
   another.  In such a case, a proxy may need to advertise both primary
   and backup routes.

   It may be also important to synchronize state information between
   primary and backup proxies since without proper HIP associations a
   backup proxy cannot correctly take place of the primary proxy to
   process the packets.  The state synchronization problem has been
   discussed above and is not dicussed here in detail.  However, if
   there is no state synchronization, a backup proxy MAY select to send
   signaling packets to HIP hosts to initiate new HIP BEXs.



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   In the remainder of this section, we discuss the operations of
   different types of HIP proxies in achieving dynamic load balancing
   and redundancy without the assistance of load balancers.

6.1.  Operations of DI-HIT Proxies

   As mentioned in section 3.1, a DI-HIT proxy needs to at least
   advertise two primary routes in the private network, a route of a
   section of HITs for intercepting data packets, and a route of a
   section of IP addresses for intercepting DNS lookups.  When the proxy
   cannot work properly, it can withdraw both routes to enable a backup
   proxy to take over its job.

   In some cases, a DI-HIT proxy may only want to delegate a part of its
   job to others so as to reduce the load it undertakes.  To achieve
   this objective, the proxy can divide its routes into multiple more
   detailed routes.  When the load on the proxy is high, it can only
   withdraw a subset of the routes.  For instance, a DI-HIT proxy can
   selectively only delegate a part of the responsibility in processing
   DNS lookups to a backup proxy by withdrawing one of its lookup
   intercepting routes.

6.2.  Operations of DI-NAT Proxies

   A DI-NAT proxy needs to at least advertise two primary routes in the
   private network, a route for its IP address pool, used to intercept
   data packets, and a route for an IP address section used to intercept
   DNS lookups.  When the proxy is overloaded, it can withdraw both
   routes so that the associated backup proxy can take over the job.  In
   this case, the delegated backup proxy needs to maintain an IP address
   pool identical to the one maintained by the primary proxy.  Moreover,
   apart from synchronizing HIP associations, the synchronization of
   mappings from IP addresses to HITs is also required.  Otherwise, the
   backup proxy cannot process the received packet correctly.

   If a DI-NAT proxy only intends to maintain existing communication
   between LHs and HIP hosts while not facilitating any more, it can
   withdraw the lookup intercepting route.  As mentioned previously, DI-
   NAT proxies have the capability to stick the DNS lookups and the
   subsequent data packets to the same proxy.  Therefore, the backup
   proxy can intercept DNS lookups as well as process the subsequent
   communication.

6.3.  Operations of DI-Transparent Proxies

   Unlike DI-HIT and DI-NAT proxies, the routes advertised by a DI-
   transparent proxy are used for intercepting both DNS lookups and data
   packets.  Therefore, before a DI-transparent proxy withdraws a route,



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   it needs to synchronize the states of the on-going communication
   affected by the routing adjustment to its backup proxies.


7.  Conclusions

   This document mainly analyzes and compares the performance of
   different kinds of HIP proxies in LBMs.  Amongst the HIP proxies
   discussed in the document, DI-NAT proxies show their advantages in
   multiple scenarios.  In addition, we argue that the state
   synchronization among HIP proxies is very important to achieve load
   balancing and redundancy.  A topic which is important but not covered
   in this document is the compatibility between different HIP proxies.
   The different types of HIP proxies are designed based on different
   presumptions.  The presumptions of different type of HIP proxies may
   be in conflict with each other.  How to make a trade-off and enable
   different types of proxies to work cooperatively is an important
   issue that the designers of HIP extensible solutions should consider.


8.  IANA Considerations

   This document makes no request of IANA.


9.  Security Considerations

   One design objective of HIP is to provide peer-to-peer security
   between communicating hosts.  However, when a HIP host communicates
   with a LH under the assistance of a HIP proxy, the security of the
   communication between the HIP proxy and the LH may not be protected.
   If the HIP proxy is transparent to the HIP host, the host will
   believe that it is communicating with a ordinary HIP host and will
   not realize that the peer-to-peer security between it and the LH is
   not guaranteed.  This may cause potential security risks, especially
   when the HIP proxy is located in the public network.  Therefore, some
   solutions should be provided for a HIP host to detect whether it is
   actually communicating with HIP proxy.

   When sharing HIP state information amongst HIP proxies, the integrity
   and confidentiality of the state information should be protected.
   The discussion about the similar issues can be found in [Nir2009]and
   [Narayanan07].

   If a HIP proxy is deployed at the border of a private network or
   within the boundary of a private network, the security issues with
   the communication between the proxy and LHs are not serious.
   However, if a proxy is deployed in the public network, both the



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   communication between LHs and the proxy and the communication between
   the proxy and DNS servers should be secured.


10.  Acknowledgements

   Thanks to Tom Henderson for his kindly proof-reading and comments.


11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5205]  Nikander, P. and J. Laganier, "Host Identity Protocol
              (HIP) Domain Name System (DNS) Extensions", RFC 5205,
              April 2008.

   [RFC5338]  Henderson, T., Nikander, P., and M. Komu, "Using the Host
              Identity Protocol with Legacy Applications", RFC 5338,
              September 2008.

11.2.  Informative References

   [Narayanan07]
              Narayanan, V., "IPsec Gateway Failover and Redundancy -
              Problem Statement and Goals", 2007.

   [Nir2009]  Nir, Y., "IPsec High Availability Problem Statement",
              2009.

   [PAT07]    Salmela, P., Wall, J., and P. Jokela, "Addressing Method
              and Method and Apparatus for Establishing Host Identity
              Protocol (Hip) Connections Between Legacy and Hip Nodes,
              US. 20070274312", 2007.

   [SAL05]    Salmela, P., "Host Identity Protocol proxy in a 3G
              system", 2005.

   [TSC05]    Tschofenig, H., Gurtov, A., Ylitalo, J., Nagarajan, A.,
              and M. Shanmugam, "Traversing Middleboxes with the Host
              Identity Protocol", 2005.



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Internet-Draft        Investigation in HIP Proxies            March 2012


Authors' Addresses

   Dacheng Zhang
   Huawei Technologies Co.,Ltd
   HuaWei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District
   Beijing,   100085
   P. R. China

   Phone:
   Fax:
   Email: zhangdacheng@huawei.com
   URI:


   Xiaohu Xu
   Huawei Technologies Co.,Ltd
   HuaWei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District
   Beijing,   100085
   P. R. China

   Phone:
   Fax:
   Email: xuxh@huawei.com
   URI:


   Jiankang Yao
   CNNIC
   4, South 4th Street, Zhongguancun
   Beijing,   100190
   P.R. China

   Phone:
   Fax:
   Email: yaojk@cnnic.cn
   URI:


   Zhen Cao
   China Mobile
   32 Xuanwumenxi Ave,Xuanwu District
   Beijing 100053
   P.R. China

   Email: zehn.cao@gmail.com, caozhen@chinamobile.com






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