[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05

Network Working Group                                           D. Zhang
Internet-Draft                                                     X. Xu
Intended status: Informational               Huawei Technologies Co.,Ltd
Expires: April 26, 2011                                           J. Yao
                                                                   CNNIC
                                                        October 23, 2010


                      Investigation in HIP Proxies
                      draft-irtf-hiprg-proxies-01

Abstract

   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 communications between legacy (or Non-
   HIP) hosts and HIP hosts while not modifying their protocol stacks.
   In this document, the legacy hosts served by proxies are referred to
   as the Made-up Legacy (ML) hosts.  Currently, various designing
   solutions of HIP proxies have been proposed.  These solutions may be
   applicable in different working circumstances.  In this document, we
   attempt to investigate these solutions in detail and compare their
   performances in different scenarios.

Requirements Language

   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].

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 April 26, 2011.

Copyright Notice



Zhang, et al.            Expires April 26, 2011                 [Page 1]


Internet-Draft        Investigation in HIP Proxies          October 2010


   Copyright (c) 2010 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.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminologies  . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  HIP Proxies  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Essential Operations of HIP Proxies  . . . . . . . . . . .  5
     3.2.  A Taxonomy of HIP Proxies  . . . . . . . . . . . . . . . .  5
     3.3.  DI Proxies . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.4.  N-DI Proxies . . . . . . . . . . . . . . . . . . . . . . .  8
     3.5.  DNS Resolvers Supporting HIP Proxies . . . . . . . . . . .  9
   4.  Issues with LBMs in Supporting ML Hosts to Initiate
       Communication  . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  An Issues Caused by Intercepting DNS Lookups . . . . . . . 10
     4.2.  Issues with LBMs in Capturing and Processing Replies
           from HIP hosts . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Issues with LBMs which also Support HIP Hosts to Initiate
       Communication  . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.1.  DNS Resource Records for ML Hosts  . . . . . . . . . . . . 13
     5.2.  An Asymmetric Path Issue . . . . . . . . . . . . . . . . . 14
   6.  Issues with LBMs in supporting dynamic load balance and
       redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  Application of DI1 proxies in supporting dynamic load
           balance and redundancy . . . . . . . . . . . . . . . . . . 17
     6.2.  Application of DI2 proxies in supporting dynamic load
           balance and redundancy . . . . . . . . . . . . . . . . . . 17
     6.3.  Application of DI3 proxies in supporting dynamic load
           balance and redundancy . . . . . . . . . . . . . . . . . . 18
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     11.2. Informative References . . . . . . . . . . . . . . . . . . 19



Zhang, et al.            Expires April 26, 2011                 [Page 2]


Internet-Draft        Investigation in HIP Proxies          October 2010


   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20


















































Zhang, et al.            Expires April 26, 2011                 [Page 3]


Internet-Draft        Investigation in HIP Proxies          October 2010


1.  Introduction

   As core components of HIP extensional solutions, HIP proxies have
   attracted increasing attention from both the industry and the
   academia.  Currently, multiple research work is engaged in the design
   and the performance assessment of HIP proxies.  In this document, we
   attempt to investigate several important designing solutions and
   compare their effectiveness in different scenarios.  Actually, there
   has 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 necessary of extending
   the HIP RR for HIP proxies) are discussed in the draft.
   Theoretically, ML hosts and the HIP hosts they intend to communicate
   with can be located anywhere in the network.  However, in this
   document, without mentioned otherwise, legacy hosts are located
   within a private network and HIP hosts are located in the public
   network, as 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 terminologies used in this document.  In section 3, we
   indicate the essential functions of HIP proxies and provide a
   classification.  In section 4, we analyze the issues that HIP
   proxies have to face in constructing a Load Balancing Mechanism (LBM)
   which facilitates communications initiated by ML hosts.  Section 5
   analyzes the issues that HIP proxies in a LBM have to face if they
   also need to support communications initiated by HIP hosts.  In
   section 6, we investigate the issues that HIP proxies have to deal
   with in supporting dynamic load balancing and redundancy.  Section 7
   provides a brief discussion about the influence brought by DNSsec to
   the deployment of HIP proxies.  Section 8 is the conclusion of the
   entire document.


2.  Terminologies

   BEX: HIP Base Exchange

   DI Proxy: DNS Inspecting Proxy

   HA: HIP association

   LBM: Load Balancing Mechanism

   N-DI proxy: Non-DNS Inspecting Proxy





Zhang, et al.            Expires April 26, 2011                 [Page 4]


Internet-Draft        Investigation in HIP Proxies          October 2010


3.  HIP Proxies

3.1.  Essential Operations of HIP Proxies

   A primary function of HIP proxies is to exchange messages with HIP
   hosts on the performance of legacy hosts, using standard HIP
   protocols.  In order to achieve this, a HIP proxy needs to intercept
   the packets transported between legacy 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 host which the packet is destined for.  Assume a proxy captures a
   packet sent out by a ML host.  If the packet is destined to a HIP
   host, the proxy first checks whether there is an appropriate HIP
   association (HA) in its local database which can be used to process
   the packet.  If such a HA is located, the proxy then find the proper
   key maintained in the HA and use it to encrypt the payload in the
   packet.  The packet is then forwarded to the HIP host.  However, if
   there is no such an HA or it has expired, the proxy needs to use the
   HI and HIT assigned to the ML host 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.  After capturing packet
   from a HIP host, the proxy also needs to use the keying material in
   the associated HA to decrypt the packet, transfer it into an ordinary
   IP packet, and forwards the IP packet to the legacy host.

3.2.  A Taxonomy of HIP Proxies

   In practice, there are various design solutions for HIP proxies.
   These solutions are based on different presumptions and supposed to
   execute in different circumstances.  To benefit the analysis, we
   classify HIP proxies into DNS lookups Intercepting Proxies (DI
   proxies) and Non-DNS lookups 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 legacy
   hosts and HIP hosts, while N-DI proxies do not have to.

   To avoid confusion, in the remainder of this document we use the
   terms "lookup" and "answer" 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 legacy host communicates with a remote host, it
   needs to query DNS servers to obtain the IP address of its
   destination.  On this premise, a DI proxy can effectively identify
   the hosts which legacy hosts may contact in near future by



Zhang, et al.            Expires April 26, 2011                 [Page 5]


Internet-Draft        Investigation in HIP Proxies          October 2010


   intercepting DNS lookups.  In practice, it is common to deploy one
   more multiple local DNS servers (resolvers) for a private network.
   Therefore, the hosts in the network can send their queries to the
   resolver instead of communicating with authoritative DNS servers
   directly.  If the resolver does not cache the inquired RRs, it will
   try to obtain them from authoritative DNS servers.  The resolver may
   have to contact multiple authoritative DNS servers to get the IP
   address of the authoritative DNS server which actually contains
   desired DNS RRs.  If the resolver is located out of the private
   network, a HIP proxy located at the border of the network can
   intercept an initial DNS query from a legacy host and then use the
   FQDN obtained from the query to initiate a new DNS lookup with 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, IPs addresses) in the local
   database, 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 can be located on the path
   between ML hosts and the resolver, it can work exactly as same as
   what is illustrated above.  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, it has to spend more
   efforts to intercept and modify 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.
   In this case, to be more efficient, the proxy can only inspect the
   responses from DNS services 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 sever 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 DNS answers for resolvers or
   ML hosts in order to benefit their following up operations.  For
   instance, [RFC5338] indicates that a HIP proxy can returns HITs
   rather than IP addresses in DNS answers to ML hosts.  Consequently,
   the data packets from ML hosts to HIP hosts will use the HITs of the
   HIP hosts as destination addresses.  [PAT07] also proposes a proxy



Zhang, et al.            Expires April 26, 2011                 [Page 6]


Internet-Draft        Investigation in HIP Proxies          October 2010


   solution which requires a HIP proxy to maintain an IP address pool.
   When sending a DNS answer to a ML host, the proxy selects an IP
   address from its pool and inserts it in 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 selected IP
   address as the destination address.  In the remainder of this
   document, these two types of proxies are referred to as DI1 proxies
   and DI2 proxies respectively, and the 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 DI3 proxies.

   Different modifications on DNS answers introduce different influences
   on the performances of DI proxies and impose different restrictions
   on their locations.

   Compared with DI1 and DI2 proxies, DI3 proxies show their limitations
   in many aspects.  For instance, it is a practical solution for a ML
   host to publish the IP address of its proxy in its DNS AAAA RR so
   that the packets for the host will be directly forwarded to the
   proxy.  Therefore, when a ML host served by a DI3 proxy attempts to
   communicate with two remote ML hosts 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, DI3 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 DI1 or DI2 proxies, these issues can be largely
   mitigated as the IP addresses of HIP hosts will never be used by DI1
   or DI2 proxies to identity hosts.

   Moreover, it is difficult for DI3 proxies to advertise routing
   information to attract the packets they needs to process (i.e., the
   packets transported between ML hosts and remote HIP hosts).
   Consequently, they can be only deployed at the borders of private
   networks.  DI1 (or DI2) proxies, however, can attract the packets for
   HIP hosts to themselves by advertising associated routes, because the
   packets destined to HIP hosts use HITs (or the IP addresses selected
   from pools) as their destination addresses.  Hence, they can locate
   inside the networks.  Therefore, in a private network whose resolver
   are located inside, a DI1 or a DI2 proxy can be deployed on the path
   between the resolver and legacy hosts, and it needs only to
   intercept, modify and forward the queries from legacy host to the
   resolver.  Compared with deploying HIP proxies at the border of the
   network, this deploying solution can reduce the overhead on the proxy
   imposed by intercepting DNS lookups.






Zhang, et al.            Expires April 26, 2011                 [Page 7]


Internet-Draft        Investigation in HIP Proxies          October 2010


3.4.  N-DI Proxies

   Unlike DI proxies, an N-DI proxy does not attempt to find out the HIP
   hosts a legacy host may contact in advance by intercepting DNS
   lookups transported between legacy hosts (or resolvers) and DNS
   servers.  Instead, it identifies whether the receiver of a packet is
   HIP enabled when it capture the packet.  Typically, an N-DI proxy
   achieves this by inspecting the destination address of the packet.
   When the HIP hosts that ML hosts intend to contact are predicable and
   the number of the HIP hosts is finite, an N-DI proxy can maintain a
   list of mapping information between HITs and IP addresses[SAL05].
   After intercepting a packet from a legacy host, the proxy can ensure
   the packet is for a HIP host, if the destination address of the
   packet is maintained in the list.  Obviously, this solution is
   infeasible in the circumstances where it is difficult to identify the
   HIP hosts that ML hosts intend to contact in advance.  On such
   occasions, an N-DI proxy has to find out whether a packet from a ML
   host is destined to a HIP host and or a legacy host.  It is
   infeasible for an N-DI proxy to consult resolution systems to find
   out whether an IP address belongs to a HIP host or a legacy host.
   Therefore, the N-DI proxy has to maintain to list of IP addresses.
   One is for HIP hosts, and the other is for legacy hosts.  When
   intercepting a packet, the N-DI can compare the destination address
   of the packet against the addresses in the lists to find out whether
   the packet is destined to a HIP host.  If no address is matched, the
   proxy has to consult resolution systems and maintain the address in
   the associated list according the answer from resolution systems.
   Obviously, an N-DI proxy may have to maintain a large amount of state
   information, which makes it less efficient and scaleable than DI-
   proxies.  Fortunately, this issue can be mitigated by inserting HITs
   instead of IPv6 addresses in the AAAA RRs of HIP hosts in DNS
   servers.  When receiving an answer containing the AAAA RR of a HIP
   host (e.g., host B), a legacy host (e.g., host A) will regard the HIT
   in the answer as the IPv6 address of B. Afterwards, when A sends a
   data packet to B, it use the HIT of B as the destination address.
   Because HITs share a prefix which is different from those of ordinary
   IP addresses, when an N-DI proxy (e.g., proxy P) catches the packet,
   P can easily distinguish it from the packets for legacy hosts.  In
   addition, P can advertise a route of the prefix of HITs within the
   private network so as to avoid dealing with the packets transported
   between legacy hosts.  After processing the packet, P may need to get
   the associated IP address from resolution servers which provide ID to
   locator mapping information (e.g., DHT servers), using the HIT found
   in the packet header.  Otherwise, P can try to send the packet to an
   overlay which supports HIT-based routing in the public network (e.g.,
   HIP Bone).

   Compared with DI proxies, N-DI proxies can be deployed in a more



Zhang, et al.            Expires April 26, 2011                 [Page 8]


Internet-Draft        Investigation in HIP Proxies          October 2010


   flexible way.  For instance, in order to facilitate the legacy hosts
   in the private networks without HIP proxies to communicate with HIP
   hosts, Internet services providers (ISPs) may deploy HIP proxies in
   transit networks.  If DI proxies are adopted, they need to locate in
   the places where they can intercept all the packets transported
   inside the transit network to find out DNS lookups because the IP
   addresses of DNS servers are normally unknown in advance.  The jobs
   of processing packets are cumbersome.  In addition, such locations
   may be quite difficult to find out.  In this case, N-DI proxies show
   their advantages; an N-DI proxy can advertise a route of the HIT
   prefix (or a sub-prefix of HIT) in the transit network and easily
   attract the desired packets to it.  Therefore, they can be deployed
   in a more flexible way and have to process fewer packets.  However,
   there is a realistic problem which may prevent N-DI proxies from
   being widely employed.  It is predicable that, in the initial period
   of widely deploying HIP hosts, various HIP proxy solutions will be
   adopted by different organizations and the information of HIP hosts
   in DNS servers will organized in an ad hoc way.  At least in this
   period, it is extremely difficult to guarantee that all the RRs of
   HIP hosts are modified appropriately.  This issue makes it difficult
   for N-DI proxies to effectively distinguish packets for HIP hosts
   from those for legacy packets.  From this perspective, the capability
   of DI proxies in modifying DNS answers is desirable.

3.5.  DNS Resolvers Supporting HIP Proxies

   As discussed above, DI proxies have to intercept and modify the DNS
   communications between legacy hosts and DNS servers in order to
   facilitate the communications between legacy hosts and HIP hosts.
   This requires a DI proxy be deployed on the boundary of the private
   network or on the path between legacy hosts and the DNS resolver.
   Such inflexibility may be undesired under certain circumstances.  In
   this section, we analyze a design option of DI proxies which improve
   the deployment flexibility of DI proxies by separating the DNS
   related functionality ( i.e., intercepting and modifying the DNS
   communications from DI proxies to DNS resolvers) from DI proxies and
   implementing it in DNS resolvers.

   A resolver extended to support a DI1 proxy returns HITs in DNS
   answers to ML hosts.  Therefore, the associated DI1 proxy can
   advertise routing information inside the private network to attract
   the packets using HITs as destination addresses.  Additionally, the
   resolver needs to transfer other information (e.g, IP addresses of
   the HIP hosts and RVSes) of the HIP hosts to the DI1 proxy so that
   the proxy can perform BEXes with the HIP hosts on behavior of ML
   hosts.

   A resolver extended to support a DI2 proxy needs to not only return



Zhang, et al.            Expires April 26, 2011                 [Page 9]


Internet-Draft        Investigation in HIP Proxies          October 2010


   the IP addresses in the address pool of the DI2 proxy but also
   transfer the mapping information of the IP addresses and the HIs to
   the DI2 proxy.  Moreover, the resolver may have to maintain the
   mapping information so as to avoid associated multiple HIs with a
   single IP address.  A resolver extended to support a DI3 proxy needs
   not to modify DNS answers, but it needs to transport the IP addresses
   of HIP hosts and their HIs to the DI2 proxy.  Therefore, this
   solution cannot make the development of DI3 proxies more flexible.


4.  Issues with LBMs in Supporting ML Hosts 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 it the
   bottleneck of the whole mechanism.  A typical solution to mitigate
   this issue is to organize multiple proxies to construct a LBM.  By
   sharing overheads amongst multiple HIP proxies, a LBM can be more
   scalable and capable to tolerate the failures of a sub-set of HIP
   proxies.  However, a LBM is not just a collection of multiple HIP
   proxies.  Lots of issues need to be carefully considered.

   Generally, there are two solutions to share communication between ML
   hosts and HIP hosts among different HIP proxies.  The first solution
   is to divided the ML hosts in the private network into different
   groups (e.g., according to their IP addresses), and the ML hosts in
   different sections are taken in charge of 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 ML hosts in the private network but
   only take in charge of the packets to and from the HIP hosts in a
   group.  Abstractly, the two solutions are identical.  However, the
   first solution actually attempts to divide a private network 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 is
   more preferred.  In the remainder of this document, we mainly
   consider the second one.

4.1.  An Issues Caused by Intercepting DNS Lookups









Zhang, et al.            Expires April 26, 2011                [Page 10]


Internet-Draft        Investigation in HIP Proxies          October 2010


   +--------------------+           +------------------+
   |                    |           |                  |
   |                +---+-------+   |                  |
   | +-----------+  |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.  In this mechanism, n proxies are
   deployed at the border of a private network.  If such proxies are DI1
   proxies, in order to share the overheads of processing data packets,
   each proxy needs to advertise a route of the HIT section it takes in
   charge of.  In addition, each proxy also needs to advise 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 DI3
   proxies, then each 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 DI3 proxy
   intercepting the lookups for the HIP host will not be the one
   intercepting subsequent data packets.  Therefore, DI3-proxy-based
   LBMs also suffer from a same problem with DI1-proxy-based LBMs.

   A candidate solution to the problem is to propagate the mapping
   information obtained from DNS lookups amongst HIP proxies.
   Therefore, after intercepting a DNS conversation, a proxy can forward
   the gained 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 addition
   overheads to DI-proxies in communicating with resolution servers.

   If the proxies in Figure 1 are DI2 proxies, the problem can be
   eliminated.  In a DI2-proxy-based LBM, each DI2 proxy needs to
   advertise two routes, one of the IP addresses in the pool and one of
   a section of IP addresses for intercepting DNS lookups.  After
   intercepting a DNS lookup, a DI2 proxy will return an IP address
   within the pool in the answer to the requester (a ML host or a



Zhang, et al.            Expires April 26, 2011                [Page 11]


Internet-Draft        Investigation in HIP Proxies          October 2010


   resolver), which can ensure the subsequent data packets will be
   transported to the same proxy.

   The DNS resolvers supporting DI proxies can simply address the issue
   by forwarding the mapping information obtained from DNS lookups to
   appropriate HIP proxies.

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

   Theoretically, when representing a ML host to communicate with a HIP
   host in the public network, a HIP porxy can use either an IP address
   it possesses or the IP address of the ML host as the source address
   of the packets forwarded to the HIP host.  However, in practice, the
   succeeding option may cause several issues.  For instance, in the
   succeeding option, a Hip proxy must be placed on the path of the
   packets transferred between HIP hosts and the ML hosts it serves in
   order to capture the reply packets from HIP hosts.  In addition, the
   succeeding solution may cause problems in the load balancing
   scenarios where multiple HIP proxies provide services for a same
   group of ML hosts.  Assume there are two HIP proxies located at the
   border of a private network.  If the proxies adopt the succeeding
   solution, they need to advertise the routes of the ML hosts 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 stuck to a same HIP proxy, and thus after a proxy intercepts
   a packet it may lack the proper HIP association to process it.

   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-in-time fashion.
   However, during communication, some context information such as the
   sequence numbers of IPsec packets can change very fast.  It is
   infeasible to synchronize the IPsec message counters for every
   transmitted or received IPsec packet, since such operations will
   occupy large amounts of bandwidth and seriously affect the
   performances of HIP proxies.  [Nir 2009] indicates that this issue
   can be partially mitigated by synchronizing IPsec message counters
   only at regular intervals, for instance, every 10,000 packets.

   An issue similar with 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 middle boxes obtain
   the SPIs used in a HIP base exchange and cannot be directly used to
   address the issue mentioned above.

   Note that all these issues can be simply addressed by adopting the
   preceding option because it can guarantee the packets transported



Zhang, et al.            Expires April 26, 2011                [Page 12]


Internet-Draft        Investigation in HIP Proxies          October 2010


   between a ML host and a HIP host are intercepted by a same proxy.
   Therefore, in the following discussions, without mentioned otherwise
   we assume that a HIP proxy uses one of its IP addresses as the source
   IP address of a packet which it sends to a HIP host.


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

   Apart from the basic functions (i.e., supporting ML hosts to
   communicate 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 conditions where HIP hosts proactively initiate
   communication with legacy hosts.

   In order to support the communication initiated by HIP hosts, the HIP
   proxies of a private network should have the knowledge essential to
   represent the ML hosts to perform HIP BEXs.  Such knowledge consists
   of the IP addresses of the legacy hosts, their pre-assigned HITs, the
   corresponding HI key pairs, and any other necessary information.  In
   addition, such information of the ML hosts 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 ML host in the opportunistic
   model which, however, should only be adopted in secure environments.

5.1.  DNS Resource Records for ML Hosts

   In practice, the AAAA RR of a ML host can consist of either the IP
   address of the ML host or the address of its HIP proxy.  In the
   preceding case, the packets destined to a legacy host are transported
   to the host directly, and thus HIP proxies must be located on the
   path of such packets to intercept them.  In the succeeding case, the
   packets for a legacy host are firstly transported to the associated
   HIP proxy.  Therefore the proxy can be deployed anywhere desired.  In
   addition, the succeeding approach is more efficient than the
   preceding one in private networks where legacy hosts and HIP hosts
   are deployed in an intermixed way, since the HIP proxy will not have
   to process the packets transported between HIP hosts.  However, the
   succeeding approach may cause problems in the process of packets sent
   by legacy hosts in the public network.  Normally, a HIP proxy needs
   to serve a number of ML hosts.  When using the succeeding approach,
   the packets destined to these ML hosts 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 ML host which the
   packet should be forwarded to.




Zhang, et al.            Expires April 26, 2011                [Page 13]


Internet-Draft        Investigation in HIP Proxies          October 2010


   A simple approach which combines the advantages of the above two
   solutions but avoids their disadvantages is to extend the RDATA field
   in HIP RRs [RFC5205] with a new proxy field, which contains the IP
   address of a HIP proxy.  In the extended HIP RR of a ML host, 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 ML host 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.

   Although it is also possible to use the RVS field in a HIP RR to
   transport the information of a HIP proxy, a special proxy field can
   bring additional benefits in security.  For instance, it is normally
   assumed that the base-exchange 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 made up 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 specific way.

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 DI1 proxies and their IP addresses are maintained
   in the DNS RRs of the ML hosts.  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 forwards it to the legacy host.  In the forwarded packets,



Zhang, et al.            Expires April 26, 2011                [Page 14]


Internet-Draft        Investigation in HIP Proxies          October 2010


   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 DI1 proxies, DI3 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 sharing HIP
   associations and IPsec association amongst HIP proxies can be used to
   address this issue.  However, this issue will introduce addition
   communication overhead on HIP proxies.  Here, we discuss several
   other alternative solutions.

   The simplest solution is to allow a HIP proxy to discard the I1
   packets it receives if they are not original from HIP hosts which the
   proxy takes in charge of.  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 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 ML host, 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 even exacerbated.

   A solution which is able to avoid the delay issue is to endow DNS



Zhang, et al.            Expires April 26, 2011                [Page 15]


Internet-Draft        Investigation in HIP Proxies          October 2010


   servers with the capability of returning the IP address of an
   appropriate HIP proxy in an answer according to the HIT (if the proxy
   is a DI1 proxy or a N-DI proxy) or the IP address (if the proxy is a
   DI3 proxy) of a requester.  That is, the HIP proxy described in a DNS
   answer should take in charge of the namespace section which the
   requester belongs to.  In order to achieve this, DNS servers need to
   1) maintain the information about the sections of the namespaces that
   HIP proxies take in charge of, 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 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.

   It is also possible to register HIP proxies to a RVS server.
   Therefore, upon receiving an I1 packet, the RVS server can forward it
   to a proper proxy to process.

   The asymmetric path issue can be eliminated by adopting DI2 proxies.
   A DI2 proxy located at the border of a private network maintains a
   pool of IP addresses which are routable in the private network.
   After receiving a packet from a HIP host, the DI2 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 responding
   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 LBMs in supporting dynamic load balance and redundancy

   The load balancing solutions discussed above are simple and static.
   They cannot modify routes of packets according to the loads on
   different HIP proxies.  In practice, there are requirements for LBMs
   to support dynamic load balance and redundancy.  That is, when a
   proxy (called a prim proxy) in a LBM is not able to work properly or
   the overheads imposed on it surpass a threshold, the proxy can
   delegate all of (or a part of) its job to other proxies (called
   backup proxies).  In this section, we analyze the performance of
   different types of HIP proxies in supporting dynamic load balance and
   redundancy.

   In order to provide backup services, a backup proxy needs to
   advertise the same routes as those advertised by the prim proxy in
   both the private and the public networks.  To avoid affecting the
   normal operations of the prim proxy, the routes advertised by the
   backup proxy have a much higher cost than that of the routes



Zhang, et al.            Expires April 26, 2011                [Page 16]


Internet-Draft        Investigation in HIP Proxies          October 2010


   advertised by the prim proxy.  When the abnormal conditions mentioned
   above occurs, the prim proxy can withdraw the routes it previously
   advertised so that the packets supposed to be processed by the prim
   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
   achieve its primary job as the prim routes of the proxy.  In
   practice, the proxies in a LBM can provide backup services for one
   another.  Therefore, a proxy in such a LBM may needs to advertise
   both prim and backup routes.

   The synchronization of state information between prim and backup
   proxies is also very important.  Without proper HIP associations, a
   backup proxy cannot correctly take place of the prim proxy to process
   the packets.  The state synchronization problem has been discussed
   above.  If there is no state synchronization, a backup proxy may
   select to send signaling packets to HIP hosts to initiate new HIP
   BEXs.

   In the remainder of this section, we attempt to analyze the
   performance of different types of HIP proxies in supporting dynamic
   load balance and redundancy respectively.

6.1.  Application of DI1 proxies in supporting dynamic load balance and
      redundancy

   As mentioned in section 3.1, a DI1 proxy needs to at least advertise
   two prim routes in the private network, one for a section of HITs,
   which is used to intercept data packets, and the other for a section
   of IP addresses, which is used to intercept 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 DI1 proxy may only want to delegate a part of its
   job to others so as to reduce the overloads it undertakes.  To
   achieve this objective, the proxy can advertise multiple specific
   prim routes.  When the overload on the proxy is high, it can only
   withdraw a subset of those advertised routes.  For instance, a DI1
   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.  Application of DI2 proxies in supporting dynamic load balance and
      redundancy

   A DI2 proxy needs to at least advertise two prim routes in the
   private network, a route for its IP address pool, used to intercept
   data packets, and the other for an IP address section, is used to



Zhang, et al.            Expires April 26, 2011                [Page 17]


Internet-Draft        Investigation in HIP Proxies          October 2010


   intercept DNS lookups.  When the proxy cannot work properly, it can
   withdraw both routes to enable a backup proxy to take over its job.
   In this case, the delegated backup proxy needs to maintain an IP
   address pool identical to the one maintained by the prim proxy.
   Moreover, apart from synchronizing HIP associations, the
   synchronization of mappings from IP addresses to HITs is also
   required.  Otherwise, the backup proxy cannot translate the received
   packet correctly.

   If a DI2 proxy only intends to maintain existing communications
   between ML hosts and HIP hosts while not facilitating any more, it
   can withdraw the lookup intercepting route.  As mentioned previously,
   DI2 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
   communications.

6.3.  Application of DI3 proxies in supporting dynamic load balance and
      redundancy

   Unlike DI1 and DI2 proxies, the routes advertised by a DI3 proxy are
   used for intercepting both DNS lookups and data packets.  Therefore,
   before a DI3 proxy withdraws a route, it needs to synchronize the
   states of the on-going communications 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, DI2 proxies show its advantages in
   multiple scenarios.  In addition, we argue that the state
   synchronization among HIP proxies is very important to achieve
   academic load balancing and redundancy.  There is a topic which is
   important but not covered in this document is the compatibility among
   different HIP proxies.  The different types of HIP proxies are
   designed based on different presumptions.  The presumptions of
   different type of HIP proxies maybe conflict with each other.  Then
   how to make a trade-off and enable different types of proxies work
   cooperatively is an important issue that the designers of HIP
   extensible solutions have to consider.


8.  IANA Considerations

   This document makes no request of IANA.




Zhang, et al.            Expires April 26, 2011                [Page 18]


Internet-Draft        Investigation in HIP Proxies          October 2010


9.  Security Considerations

   Security is an important benefit introduced by HIP.  In the basic HIP
   architecture, security requirement on DNS communications is not
   compelled.  But in practice, DNSSEC [RFC4305] is recommended in order
   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, DI1 and DI2 proxies need to modify the
   contents of NDS answers, and thus they should be only deployed on the
   path between legacy hosts and their resolvers.  Therefore, a DI1
   proxy (or a DI2 proxy) should not be deployed in the middle of
   DNSsec-enabled resolvers and authoritative DNS servers.

   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 [Nir 2009]
   and [Narayanan 07].


10.  Acknowledgements


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

   [Narayanan 07]
              Narayanan, V., "IPsec Gateway Failover and Redundancy -
              Problem Statement and Goals", 2007.

   [Nir 2009]



Zhang, et al.            Expires April 26, 2011                [Page 19]


Internet-Draft        Investigation in HIP Proxies          October 2010


              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.


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:











Zhang, et al.            Expires April 26, 2011                [Page 20]


Internet-Draft        Investigation in HIP Proxies          October 2010


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

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









































Zhang, et al.            Expires April 26, 2011                [Page 21]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/