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

Versions: 00 01 draft-palet-v6tc-goals-tunneling

   Network Working Group                                      K. Nielsen
   INTERNET-DRAFT                                               Ericsson
                                                              M. Morelli
   Expires:  March 2, 2005                            Telecom Italia Lab
                                                                J. Palet
                                                             Consulintel
                                                             J. Soininen
                                                                   Nokia
                                                             J. Wiljakka
                                                                   Nokia

                                                       September 2, 2004

                   Goals for Zero-Configuration Tunneling
                 <draft-nielsen-v6ops-zeroconf-goals-01.txt>


Status of this memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668 (BCP 79).

   By submitting this Internet-Draft, I accept the provisions of Section
   [#3] of RFC 3667 (BCP 78).

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

   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 cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


Abstract

   This document describes the set of goals to be fulfilled by a Zero-
   Configuration Tunneling protocol.

   Zero-Configuration Tunneling here denotes a minimalistic IPv6-in-IPv4
   automatic tunneling mechanism that could be used by a Service



Nielsen, et al.                                                 [Page 1]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   Provider to offer IPv6 connectivity to its customers in early phases
   of IPv4 to IPv6 transition.


Table of Contents

   1. Introduction.....................................................2
   2. Terminology......................................................4
   3. Scope and Limitations............................................4
      3.1. IPv6 address allocation, Scope and Limitations:.............4
      3.2. IPv6 tunnel link characteristics, Scope and Limitations:....5
   4. Assumptions and Prerequisites....................................5
      4.1. Applicability Assumptions...................................5
      4.2. 3GPP Compliance Prerequisite................................6
   5. Timing...........................................................6
   6. Goals............................................................7
      6.1. Simplicity..................................................7
      6.2. Automated IPv6-in-IPv4 tunnel establishment.................7
      6.3. Use native when available...................................7
      6.4. Easy to deploy and Easy to Phase-out with no modifications on
      existing equipment...............................................8
      6.5. Tunnel Server End-point Discovery...........................8
      6.6. Address Assignment..........................................8
      6.7. Tunnel Link Sustainability..................................9
      6.8. Tunnel End-Point Reachability Detection.....................9
      6.9. Private and public IPv4 addresses...........................9
      6.10. Scalability, Load Balancing................................9
      6.11. Security..................................................10
   7. Non Goals.......................................................10
      7.1. NAT and Firewall Traversal.................................10
      7.2. IPv6 DNS...................................................10
      7.3. Extensibility..............................................11
      7.4. Registration burden........................................11
   8. Stateful or Stateless...........................................11
   9. Security Considerations.........................................11
      9.1. Threats to existing network infrastructures................12
      9.2. Threats to nodes implementing Zero-Configuration Tunneling.12
         9.2.1. Threats to end-hosts..................................13
         9.2.2. Threats to Tunnel Servers.............................13
            9.2.2.1. Tunnel State related risks.......................13
            9.2.2.2. Traffic related risks............................14
            9.2.2.3. Packet Delivery related threats..................14
      9.3. Implications of Direct Tunneling...........................14
   10. Acknowledgments................................................15
   11. Authors Addresses..............................................15
   12. Changes from draft-nielsen-v6ops-zeroconf-goals-00.txt.........16
   13. Informative References.........................................17
   Appendix A Out of Scope............................................18
   Appendix B Open Issues.............................................18

1. Introduction



Nielsen, et. al.                                                [Page 2]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004



   The IETF v6ops Working Group has identified and analyzed deployment
   scenarios for IPv4/IPv6 transition mechanisms in various stages of
   IPv6 deployment and IPv6 and IPv4 coexistence.

   This work has been carried out for a number of different network
   environments each with their particular characteristics: Enterprise,
   ISP, Unmanaged and 3GPP networks, see e.g., [2], [3] and [4].

   The work has identified a need for automatic IPv6-in-IPv4 tunneling
   mechanisms that provide bidirectional IPv6-in-IPv4 tunneled
   connectivity between dual stack end-nodes located at an IPv4-only
   access network and dual-stack tunnel servers located at IPv6-IPv4
   network boundaries within the Service Providers network.

   The term Zero-Configuration Tunneling is used in this document to
   denote an IPv6-in-IPv4 tunneling mechanism that fulfills the goals as
   put forward here.

   A Zero-Configuration Tunneling mechanism provides a basic set of
   tunneling features only, and intentionally so. The scope of Zero-
   Configuration Tunneling is not to provide emulation of the full suite
   of native IPv6 connectivity functions as defined by [7], [8] and [9];
   rather the focus is to provide a minimal set of features required for
   automatic establishment of IPv6 connectivity.

   The starting point for the definition of the set of goals to be
   fulfilled by a Zero-Configuration Tunneling mechanism has been the
   set of features required for the IPv6-in-IPv4 tunneling mechanism
   envisaged to be needed during the early phases of IPv6 transition in
   3GPP environments as described in [4].

   The applicability of Zero-Configuration Tunneling may widen to other
   transition scenarios.

   For scenarios demanding advanced tunneling features, for example full
   emulation of native (though tunneled) IPv6 connectivity, a more full-
   fledged tunneling mechanism is envisaged to be deployed, see [5].
   With respect to the latter, an analysis of appropriate mechanisms for
   automatic discovery of the tunnel endpoint is being done in [6].

   It should be emphasized that unless otherwise specified then in this
   document the reference, IPv6-in-IPv4 encapsulation as defined in [1],
   refers to the aspects of Protocol-41 encapsulation related to IPv4
   header construction (except for source and destination address
   determination), MTU and Fragmentation, Hop Limits and ICMP handling
   as detailed in Section 3.1-3.6 of [1]. The particular aspects of
   Configured IPv6-In-IPv4 Tunneling in the areas of IPv4 source and
   destination address determination, tunnel link characteristics and
   IPv6 Neighbor Discovery operation are not intended referred to by the
   above reference.



Nielsen, et. al.                                                [Page 3]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004




2. Terminology

   Zero-Configuration Tunneling site:
   A logical IPv4 network over which IPv6 connectivity is provided to
   dual-stack nodes by means of Zero-Configuration Tunneling.

   Tunnel End-point:
   A dual-stack node performing IPv6-in-IPv4 tunnel
   encapsulation/decapsulation in accordance with Zero-Configuration
   Tunneling.

   Tunnel Server:
   A dual-stack server node with IPv6 connectivity and which provides
   IPv6 connectivity to client nodes by performing IPv6-in-IPv4 tunnel
   encapsulation/decapsulation to/from client nodes in accordance with
   Zero-Configuration Tunneling.

   A Tunnel Server is likely to be a dual-stack router.

   Tunnel Client:
   A dual-stack node that obtains IPv6 connectivity by means of Zero-
   Configuration Tunneling. A tunnel client relies on IPv6-in-IPv4
   tunnel encapsulation/decapsulation to/from Tunnel Servers for IPv6
   communications to native IPv6 nodes.

   Direct Tunneling:
   Direct tunnelling here refer to the case where end-hosts located
   within the same Zero-Configuration Tunnelling site may circumvent the
   Tunnel Server and communicate directly using the tunnel protocol.

3. Scope and Limitations

   The scope of Zero-Configuration Tunneling is restricted to an
   absolute minimal set of functions required to provide automatic IPv6
   connectivity establishment to dual stack nodes by means of IPv6-in-
   IPv4 encapsulation as defined in [1] to tunnel servers under the
   assumptions and prerequisites described in Section 4.

   Zero-Configuration Tunneling does not attempt to provide emulation of
   the full set of native IPv6 connectivity functions as defined by [7],
   [8] and [9].

3.1. IPv6 address allocation, Scope and Limitations:

   The primary goal of Zero-Configuration Tunneling is to provide IPv6
   connectivity to nodes on an individual basis. By this it is meant
   that it is only an explicit goal to have a /128 address allocated for
   global connectivity on the tunnel link. As such optimal IPv6




Nielsen, et. al.                                                [Page 4]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   connectivity provisioning in Personal Area Network (PAN) scenarios is
   not explicitly within the scope of Zero-Configuration Tunneling.

   It is not explicitly within the scope of Zero-Configuration Tunneling
   to support usage of privacy IPv6 extensions as defined in [12].

   It is not explicitly within the scope to support usage of IPv6
   multicast.

   No goals are defined as to how address configuration should be
   performed. This may be done based on legacy stateless or stateful
   IPv6 address configuration mechanisms or by some altogether different
   mechanism particular to the zero-configuration solution.

3.2. IPv6 tunnel link characteristics, Scope and Limitations:

   Direct tunneling is neither an explicit goal nor explicitly excluded
   in Zero-Configuration Tunneling.

   It is not an explicit requirement for the zero-configuration tunnel
   link to support IPv6 link-local multicast.

   The tunnel protocol should allow for the formation of a link-local
   address on the tunnel link. Though no particular usage of such an
   address is explicitly demanded by the goals set forward here.

   It is an explicit goal that nodes attached to a tunnel link must be
   able to ascertain the reachability of neighbors with which it is
   communicating (or wish to start communicate). This may be achieved
   using IPv6 Neighbor Discovery mechanism ([13]) based on unicast link-
   local packet exchanges (or link-local multicast if such is supported)
   but it may also be achieved by altogether different mechanisms.

4. Assumptions and Prerequisites

4.1. Applicability Assumptions

   Zero-Configuration Tunneling is a tunneling mechanism by the virtue
   of which dual-stacks hosts, attached to IPv4-only networks links, can
   use IPv6-in-IPv4 encapsulation as defined in [1] to tunnel servers
   for global IPv6 connectivity.

   The aim of the document is to define the set of goals to be fulfilled
   by zero-configured tunneling when the following assumptions are made
   on the deployment environment:

      - IPv4 source addresses spoofing within the Zero-Configuration
        Tunneling site is prevented.
      - The Zero-Configuration Tunneling site is protected from proto-41
        encapsulated packets arriving from external IPv4 networks.




Nielsen, et. al.                                                [Page 5]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


      - At least one authoritative DNS server is IPv4-enabled and at
        least one recursive DNS server supports IPv4. Further IPv4 DNS
        Server discovery is provided by already existing means/means
        outside the scope of the tunnel protocol.
      - There are no NATs in between the tunnel endpoints in the Zero-
        Configuration Tunneling site.
      - The Zero-Configuration Tunneling network is fully penetrable for
        intra-site IPv6-in-IPv4 Protocol 41 traffic.
      - The user is being authenticated to the network by means external
        to the tunneling protocol and other than that no additional
        authentication/registration mechanisms are required.

   The above assumptions are believed to be readily applicable to the
   3GPP tunneling transition scenario described in [4], section 3.1.

   It is a prerequisite that the tunnel protocol must work in IPv4
   network environments where IPv4 multicast is not provided.

4.2. 3GPP Compliance Prerequisite

   It is a prerequisite that Zero-Configuration Tunneling should be
   applicable in 3GPP wireless networks. When considering the
   characteristics of 3GPP network links and mobile terminals / User
   Equipment (UE), the following points need to be taken into account:
      - Link bandwidth (tunnel overhead / usage cost)
      - Link latency
      - UE battery power and derived implications on memory and
        processing power

   It is thus an explicit requirement for Zero-Configuration Tunneling
   to comply well with the constrained conditions put on the above
   parameters by the 3GPP environments. The latter which commonly is
   recognized as translating into requirements for the protocol to
   operate with a limited number of message exchanges, small packet
   sizes and simple message processing.

   Here we shall refer to a protocol as being lightweight when its
   demands on message exchanges, packet sizes and message processing
   complexity are sufficiently light for it to be readily applicable in
   environments characterized by the constrained conditions of 3GPP
   networks (as described above).

   As a mean to ensure that the protocol be lightweight it is considered
   preferable for the protocol to provide a simple set of functions
   only, even if it provides only a basic IPv6 service compared to the
   native one. It is although acknowledged that additional functionality
   doesn't necessarily automatically add complexity to the demands on
   the aforementioned parameters.

5. Timing




Nielsen, et. al.                                                [Page 6]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   For the purpose of 3GPP deployment it is a prerequisite that this
   tunneling protocol is provided within a very restrictive timescale.

   Zero-Configuration Tunneling is envisaged to be deployed in 3GPP
   networks as an initial and temporary mechanism to provide limited
   IPv6 connectivity services. Native IPv6 like connectivity is in 3GPP
   environments envisaged to be feasible by virtue of true native IPv6
   only.

   Trial deployments, in which zero-configuration type of IPv6
   connectivity is provided in 3GPP environments, are starting up using
   experimental protocols at the time of writing this document.

6. Goals

   The goals to be achieved by Zero-Configuration Tunneling are detailed
   in the following subsections.

6.1. Simplicity

   By simplicity, we understand a tunnel protocol that is easy to
   implement in the targeted environment. Additionally, the protocol
   should provide a reasonable, limited set of basic IPv6 connectivity
   features.

   Further by simplicity we imply that the protocol must be lightweight.

6.2. Automated IPv6-in-IPv4 tunnel establishment

   The protocol should provide for the set up of IPv6-in-IPv4 tunnels,
   based on IPv6-in_IPv4 encapsulation as defined in [1], from dual-
   stack nodes, attached to IPv4-only networks, to Tunnel Servers.

   The IPv6-in-IPv4 tunnels and the IPv6 connectivity must be
   established in an automated manner, i.e. without requiring manual
   intervention at any of the tunnel end-points at tunnel establishment
   time.

   The mechanism must be fully dynamic in the sense that it must not
   require IP address information such as the IPv4 address of a Tunnel
   Server and/or the IPv6 address(es) to use for IPv6 connectivity to be
   configured on the Tunnel Clients beforehand.

6.3. Use native when available

   The tunnel protocol should allow the usage of native IPv6
   connectivity whenever such is available.

   The protocol must in no way restrict the native IPv6 capabilities of
   the client node.




Nielsen, et. al.                                                [Page 7]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   The node should not use Zero-Configuration Tunneling when native IPv6
   connectivity is available.

   Comment: The fact that a node should not use Zero-Configuration
   Tunneling when native IPv6 connectivity is available is not
   considered to be a functional requirement on the tunnel protocol.
   Rather it is considered related to when, and how, the node
   (implementation) uses the Zero-Configuration Tunneling function.

6.4. Easy to deploy and Easy to Phase-out with no modifications on
   existing equipment

   The tunnel protocol should be easy to deploy into the existing IPv4
   and IPv6 network infrastructure.

   The tunnel protocol should have no major impact on protocols and
   infrastructure nodes deployed in existing infrastructures providing
   IPv4 and native IPv6 connectivity.

   The tunnel protocol should coexist and work seamlessly together with
   any native IPv6 infrastructure that gradually may be implemented in
   the network. The tunnel protocol should have no negative implications
   on how such are implemented.

   The tunnel protocol must be easy to take out of service once native
   IPv6 is available.

6.5. Tunnel Server End-Point Auto-Discovery

   The tunnel protocol must provide a mechanism for automated end-point
   discovery by the virtue of which end-hosts automatically and at run-
   time can determine the IPv4 addresses of available Tunnel Servers.

   The discovery mechanism should rely on intrinsic services, read
   services already universally deployed, to the particular network
   environment. It should not require the addition of additional IP
   network infrastructure elements for this function only.

   Comment: The analysis done in [6] may apply.

6.6. Address Assignment

   The tunnel protocol must allow for the assignment of at least one
   globally routable (/128) IPv6 unicast address to use for tunneled
   IPv6 connectivity over the link provided by the Zero-Configuration
   Tunneling mechanism.

   It is preferable that the address assignment provides a stable
   address, that is, an address that can be used for IPv6 connectivity
   for a certain amount of time rather than solely one address per
   higher layer session initiation.



Nielsen, et. al.                                                [Page 8]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004



6.7. Tunnel Link Sustainability

   The tunnel link established in between a host deploying Zero-
   Configuration Tunneling and an associated Tunnel Server should be
   expected to remain in administrative active state for the lifetime of
   the IPv6 address provided to the host.

   The tunnel protocol must not mandate keep-alive messages to be
   transmitted by the host simply in order to sustain tunnel link
   connectivity.

   Motivation: The fact that a 3GPP terminal, for the single purpose of
   transmitting keep-alive messages, could have to wake up the radio
   periodically, send a packet over the radio and possibly wait for
   response is undesirable for the following reasons:
      - The terminal cannot, as otherwise anticipated, be in dormant
        mode all the time it is idle. This has severe implications for
        the battery consumption of the device.
      - Radio resources are costly and sparse and consequently not to be
        used for what is considered to be unnecessary traffic.

6.8. Tunnel End-Point Reachability Detection

   The tunnel protocol must allow for means for one tunnel end-point to
   verify the reachability of other tunnel end-points towards which it
   intends to send packets.

   The unicast neighbor reachability discovery functions provided by
   IPv6 Neighbor Discovery ([13]), i.e., unicast NS/NA exchanges, should
   be supported on the tunnel link.

6.9. Private and public IPv4 addresses

   The tunnel protocol must work over IPv4 sites deploying both private
   and public IPv4 addresses.

   Furthermore, the tunnel protocol should work with both dynamic and
   static IPv4 address allocation.

   Motivation: Private IPv4 addresses are widely used in current 3GPP
   networks.

6.10. Scalability, Load Balancing

   In order to ensure the scalability of the tunnel service, in terms of
   not limiting the number of simultaneous connections to the service
   and consequently limiting possible service denial situations, it
   should be possible for a Service Provider to load-balance those
   connections among several available Tunnel Servers.




Nielsen, et. al.                                                [Page 9]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   Load balancing should be planned already during the early phases of
   deployment. Given adequate planning it should be possible for a
   Service Provider to seamlessly deploy additional Tunnel Servers in
   order to support an increased amount of Tunnel Clients.

   Comment: This may be achieved using load balancing functions provided
   by the Tunnel Server End-point Discovery mechanism as detailed in
   [14].

6.11. Security

   The tunnel protocol should not impose any new vulnerability to the
   existing network infrastructure.

   The tunnel protocol should not impose any new vulnerability to the
   nodes implementing the tunnel protocol than what is already present
   in existing multi-access IPv6 networks, where multiple hosts are
   served by the same router or possibly multiple routers.

7. Non Goals

   Non-goals of zero-configured tunneling are detailed in the following
   subsections.

   With the term Non-goals we refer to features that generally are
   believed to be applicable to tunneling, but which are not among the
   minimal set of required features of Zero-Configuration Tunneling. The
   latter primarily because of the prerequisites for Zero-Configuration
   Tunneling and/or because of the assumptions made on the applicability
   environments for Zero-Configuration Tunneling, e.g., see Section 4.

7.1. NAT and Firewall Traversal

   NAT and Firewall traversal is not required due to the assumptions on
   the applicability environment.

   Moreover to minimize the tunneling overhead applied to the packets as
   well as in order to minimize the number of tunnel set-up signaling
   messages exchanged on the link, it is preferable that the protocol
   does not deploy the UDP encapsulation techniques, on which mechanisms
   able to traverse NATs and Firewalls normally rely.

7.2. IPv6 DNS

   By virtue of the assumptions on the applicability environments, the
   dual stack end-hosts can use IPv4 DNS discovery mechanisms and IPv4
   transport for DNS services.

   Given that IPv4 based DNS services are already available, it is not
   considered a requirement that the end-host should be able to deploy




Nielsen, et. al.                                               [Page 10]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   IPv6 based DNS services. Consequently, the tunnel protocol does not
   need to provide IPv6 DNS discovery mechanisms.

7.3. Extensibility

   As a minimal tunneling mechanism Zero-Configuration Tunneling targets
   IPv6 connectivity provisioning only. The protocol does not need to be
   readily extendable to other encapsulation mechanisms, e.g., IPv4-in-
   IPv6.

7.4. Registration burden

   Tunnel service registration is not required due to the assumptions on
   the applicability environment.

   In order to keep the simplicity and minimize the tunnel overhead it
   is desirable that the tunnel protocol not in itself (e.g., in order
   to meet the goals put forward in this document) mandates
   authenticated registration of the user.

8. Stateful or Stateless

   By a stateful mechanism we mean a mechanism that require the Tunnel
   Server to maintain tunnel state per client it serves.

   Tunnel state here is considered to be any parameter kept by the
   server per client and without which the server is unable to serve the
   client (receive packets from/send packets to).

   Tunnel state must be distinguished from state used to optimize the
   packet delivery function of the tunnel server and which is kept in a
   fixed or upper limited amount of memory space, such as, e.g.,
   reachability information.

   It should be emphasized that this document makes no deliberate
   assumptions on whether a Zero-Configuration Tunneling solution should
   be based on a stateful or stateless Tunnel Server mechanism. Indeed
   it is anticipated that the goals of zero-configuration as put forward
   here could be served both by a stateless as well as by a stateful
   mechanism.

9. Security Considerations

   It is assumed that the following assumptions of Section 4 are valid
   in the particular network environment:

      - IPv4 source addresses spoofing within the Zero-Configuration
        Tunneling site is prevented.
      - The Zero-Configuration Tunneling site is protected from proto-41
        encapsulated packets arriving from external IPv4 networks.




Nielsen, et. al.                                               [Page 11]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   It is worthwhile to note that together these assumptions imply that
   the IPv4 source of all protocol-41 tunneled packets is legitimate.

9.1. Threats to existing network infrastructures

   As stated in Section 6.11 the tunnel protocol should not impose any
   new vulnerability to the existing network infrastructure.

   The following have been identified as potential threats opened up for
   by the deployment of Zero-Configuration Tunneling:

      - As the tunnel service is un-authenticated (not registered) it
        may be possible to use a tunnel server to reflect tunneled
        packets into the network, similar to the 6to4-reflection attacks
        identified in [10].
      - The Zero-configuration site must be kept fully penetrable for
        intra-site IPv6-in-IPv4 protocol-41 encapsulated packets. This
        may open up for threats to end-hosts that rely on the network
        infrastructure to filter out bogus protocol-41 encapsulated
        packets.
      - Zero-configuration tunneling may open up for threats to other
        mechanisms in the network that rely on Protocol-41
        encapsulation.

   Detailed analysis of the validity of these threats will have to
   depend on the particular zero-configuration solution. In general it
   could be noted that attacks based on the above threats largely should
   be preventable if the end-hosts in the network implement appropriate
   drop policies, either simple drop all protocol-41 policies or more
   differentiated policies based, e.g., on source addresses.

9.2. Threats to nodes implementing Zero-Configuration Tunneling

   The following considerations apply to the situation where Zero-
   Configuration Tunneling is deployed in between tunnel servers and
   end-hosts only.

   Special security considerations for the usage of Zero-Configuration
   Tunneling for direct tunneling in between end-hosts is given in
   Section 9.3.

   As stated in Section 6.11 the tunnel protocol should not impose any
   new vulnerability to the nodes implementing the tunnel protocol than
   what is already present in existing multi-access IPv6 networks where
   multiple hosts are served by the same router or possible multiple
   routers.

   Here it is implicitly assumed that the tunnel server(s) take the role
   of default routers and the end-nodes using Zero-Configuration
   Tunneling for IPv6 connectivity the role of hosts in multi-access
   environments.



Nielsen, et. al.                                               [Page 12]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004



9.2.1. Threats to end-hosts

   Given that all IPv4 sources of protocol-41 tunneled packets can be
   assumed to be legitimate, threats stemming from encapsulated packets
   sourced by nodes (addresses) other than nodes (addresses) which the
   end-hosts recognize as tunnel servers (identified by addresses) can,
   if not already an intrinsic part of the zero-configuration protocol,
   easily be mitigated by the implementation of appropriate
   differentiated (source addresses) drop policies in the end-hosts,
   i.e., accept only if source is tunnel server.

   In current multi-access IPv6 networks hosts need to trust on the
   benevolence of their default routers as well as hosts must trust that
   anyone impersonating as a router is indeed one, see, e.g., the trust
   models and threats described in [11].

   Future multi-access IPv6 networks may rely on SEND mechanisms, i.e.,
   mechanisms developed in the SEND WG in order to mitigate the threats
   described in [11], to establish a trust relations ship in between
   host and routers.

   Given that IPv4 source address spoofing is not possible in Zero-
   Configuration Tunneling sites, then
      - for an end-host to trust that packets it perceives as stemming
        from tunnel servers do actually stem from such - as well as รป
      - for an end-host to trust on the benevolence of its tunnel
        servers,
   it suffices that a trustworthy tunnel server end-point discovery
   mechanism, read discovery of benevolent tunnel servers IPv4
   address(es), is implemented.

   In open environments, such as, e.g., the 3GPP environment, it is
   assumed a prerequisite that a trustworthy zero-configuration tunnel
   server end-point discovery mechanism is implemented.

9.2.2. Threats to Tunnel Servers

   Zero-Configuration Tunneling may be deployed over very large IPv4
   sites with low density of active tunnel clients but with a very high
   number of dormant, but potential tunnel clients. Therefore Denial of
   Service prevention by strict over provisioning of Tunnel Server
   capacity is unlikely to be performed.

9.2.2.1. Tunnel State related risks

   If the Tunnel Server relies on state to be kept per tunnel client
   that it serves, the server risks resource exhaustion.

   In this situation it is a security prerequisite that no node, whether
   located within or outside the Zero-Configuration Tunneling site, can



Nielsen, et. al.                                               [Page 13]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   initiate initialization of tunnel state for other entities than
   itself.

   Given this prerequisite, then for tunnel server resource exhaustion
   by tunnel state creation to be categorized as a security threat,
   rather than a case of under provisioning, requires a large number of
   tunnel clients to operate in co-action. This is thus not considered a
   plausible threat.

9.2.2.2. Traffic related risks

   Tunnel encapsulation is recognized as being more resource demanding
   than mere packet forwarding. Given the same traffic load a Tunnel
   Server must thus be more generously provisioned that a corresponding
   router for it not to be more likely to get overthrown by large
   unexpected amounts of traffic than the router.

   The authors have found no plausible treats to the tunnel service, due
   to large unexpected amounts of traffic needing encapsulation, which
   can be classified as a security threat rather than a case of under
   provision. This regardless of whether the traffic is due to a surge
   in the density of active tunnel clients or due to a surge in the
   traffic streams set-up by active clients.

9.2.2.3. Packet Delivery related threats

   One potential risk related to packet delivery has been identified.
   This risk is the equivalent of the threat to routers in multi-access
   environments described in [11], Section 4.3.2.

   The risk is associated with the special case where the tunnel
   protocol requires special resource demanding and/or temporary state
   creation actions to be taken by the Tunnel Server for delivery of
   packets destined for not recently addressed Tunnel Clients. The
   situation where such actions must be performed for all packets at all
   times is considered to be unlikely. The actions required could be
   buffering of packets while the reachability of the destined node is
   being verified.

   In case a malicious node (located either within or outside the zero-
   configuration site) is able to continuously send packets to
   continuously changing nodes, which by the Tunnel Server is perceived
   as being existing or potential client nodes, the malicious node may
   be able to exhaust the Tunnel Servers capability of delivering
   packets by saturating the packet buffering mechanism and the
   reachability state table as well as by keeping the Tunnel Server busy
   determining the reachability state of the ever changing client nodes.

9.3. Implications of Direct Tunneling





Nielsen, et. al.                                               [Page 14]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   In case direct tunneling in between end-hosts is provided by the
   tunneling protocol, it will not (as described in Section 9.2.1) be
   possibly for end-hosts to filter out received Protocol-41
   encapsulated packets based on whether the IPv4 source is an address
   belonging to a trusted Tunnel Server as such behavior evidently would
   break direct tunneling.

   As other end-hosts generally are non-trusted, direct tunneling may
   thus open up for attacks against IPv6 ingress filtering.

   Detailed analysis of the validity of this threat will have to depend
   on the particular zero-configuration solution.

10. Acknowledgments

   Prior work by J. Mulahusic on the requirements for UE tunneling has
   been considered in the initial stage of the work.

   This work has benefited from input and comments provided by Fred
   Templin in the initial phase of the work.

   Thanks are due to Pekka Savola for many helpful comments and
   suggestions for improvements.

   Corresponding work on assisted-tunneling, [5], has been an
   inspiration for the Zero-Configuration Tunneling work.

   The authors would like to acknowledge the European Commission support
   in the co-funding of the Euro6IX project, where part of this work is
   being developed.


11. Authors Addresses

              Mario Morelli
              Telecom Italia Lab.
              Via Guglilmo Reiss Romoli, 274
              I-10148 Turin,
              Italy

              Phone: +39 011 228 7790
              Fax: +39 011 228 5069
              Email: mario.morelli@tilab.com


              Karen Egede Nielsen
              Ericsson
              Skanderborgvej 232
              8260 Viby J
              Denmark




Nielsen, et. al.                                               [Page 15]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


              Phone: + 45 89 38 51 00
              Email: karen.e.nielsen@ericsson.com


              Jordi Palet Martinez
              Consulintel
              San Jose Artesano, 1
              Alcobendas - Madrid
              E-28108 - Spain

              Phone: +34 91 151 81 99
              Fax:   +34 91 151 81 98
              EMail: jordi.palet@consulintel.es

              Jonne Soininen
              Nokia
              Linnoitustie 6
              02600 ESPOO
              Finland

              Phone: +358 7180 08000
              EMail: jonne.soininen@nokia.com



              Juha Wiljakka
              Nokia
              Visiokatu 3
              33720 TAMPERE
              Finland

              Phone: +358 7180 48372
              EMail: juha.wiljakka@nokia.com




12. Changes from draft-nielsen-v6ops-zeroconf-goals-00.txt

      - Aimed to clarify what is meant by full suite of native Ipv6
        connectivity functions.

      - Aimed to clarify what is meant when referring to IPv6-in-IPv4
        encapsulation as defined in [1].

      - Aimed to clarify the accepted limitations of the IPv6
        connectivity service provided by Zero-Configuration Tunneling
        compared to the full suite of native IPv6






Nielsen, et. al.                                               [Page 16]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


      - Added that it is a prerequisite that Zero-Configuration
        Tunneling can work over IPv4 networks where Ipv4 multicast is
        not supported.

      - Clarified goal, Section 6.3, on usage of native IPv6 when
        available.

      - Added goal on load sharing and scalability, Section 6.10.

      - Added Section 8, discussing state or no state.

      - Changed Section 6.8 on reachability detection to refer to
        unicast Neighbor Discovery techniques rather than IPv6 NUD.

      - Added material to the section on threats to tunnel servers,
        9.2.2.

      - Added section, Section 9.3, discussing particular security
        considerations for usage of direct tunneling.

      - Added text under Acknowledgements

      - Specified references as informative.

      - Performed various Editorial changes.


13. Informative References

   [1]  Nordmark, E., Basic Transition Mechanisms for IPv6 Hosts and
        Routers, draft-ietf-v6ops-mech-v2-04.txt (work in progress),
        July 2004.
   [2]  Lind, M., Scenarios and Analysis for Introducing IPv6 into ISP
        Networks, draft-ietf-v6ops-isp-scenarios-analysis-03.txt (work
        in progress), June 2004.
   [3]  Huitema, C., Evaluation of Transition Mechanisms for Unmanaged
        Networks, draft-ietf-v6ops-unmaneval-03.txt (work in progress),
        June 2004.
   [4]  Wiljakka, J., Analysis on IPv6 Transition in 3GPP Networks,
        draft-ietf-v6ops-3gpp-analysis-10.txt (work in progress), May
        2004.
   [5]  Durand, A., Requirements for assisted tunneling, draft-ietf-
        v6ops-assisted-tunneling-requirements-00.txt (work in progress),
        June 2004.
   [6]  Palet, J., Analysis of IPv6 Tunnel End-point Discovery
        Mechanisms, draft-palet-v6ops-tun-auto-disc-01.txt (work in
        progress), June 2004.
   [7]  Wasserman, M., Recommendations for IPv6 in 3GPP standards, RFC
        3314.
   [8]  Loughney, J., IPv6 Node Requirements, draft-ietf-ipv6-node-
        requirements-10.txt (work in progress), August 2004.



Nielsen, et. al.                                               [Page 17]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   [9]  IAB, IESG, IAB/IESG Recommendations on IPv6 Address Allocations
        to Sites, RFC 3177.
   [10] Savola, P., Security Considerations for 6to4, draft-ietf-v6ops-
        6to4-security-04.txt (work in progress), July 2004.
   [11] Nikander, P., IPv6 Neighbor Discovery (ND) Trust Models and
        Threats, RFC 3756.
   [12] Narten, T., Privacy Extensions for Stateless Address
        Autoconfiguration in IPv6, RFC 3041.
   [13] Narten, T., Neighbor Discovery for IP Version 6 (IPv6), RFC
        2461.
   [14] Jordi, P., draft-palet-v6ops-solution-tun-auto-disc-00 (work in
        progress), September 2004.


Appendix A Out of Scope

   [Editor's Note: This appendix can be removed in a future revision of
   this document]

   The following issues have been considered as being out of scope of
   this work.

   DNS:

   DNS registration of the IPv6 addresses allocated to dual stack nodes
   while deploying Zero-Configuration Tunneling for IPv6 connectivity.

   Mobile IPv6:

   Support of Mobile IPv6 usage over the tunnel-link; here under
   potential mechanisms required to support MIPv6 movement detection as
   well as fast tunnel set-up for Mobile IPv6 session survivability.


Appendix B Open Issues

   [Editor's Note: This appendix can be removed in a future revision of
   this document]

   Allow NATs that support proto-41 forwarding:
   Should the no NATs assumption be relaxed to allow only NATs which
   support proto-41 forwarding ?



Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights



Nielsen, et. al.                                               [Page 18]


INTERNET-DRAFT          Zeroconf Tunneling Goals        September, 2004


   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights. Information
   on the IETF's procedures with respect to rights in IETF Documents can
   be found in RFC 3667 (BCP 78) and RFC 3668 (BCP 79).

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

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


Copyright Statement

   Copyright (C) The Internet Society (2004). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.



This Internet-Draft expires March 2, 2005.















Nielsen, et. al.                                               [Page 19]


Html markup produced by rfcmarkup 1.120, available from https://tools.ietf.org/tools/rfcmarkup/