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Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Expires: November 22, 2004                                  May 24, 2004

               Things MULTI6 Developers should think about

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.

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Copyright Notice

    Copyright (C) The Internet Society (2004). All Rights Reserved.


    This document specifies a set of questions that authors should be
    prepared to answer as part of a solution to multihoming with IPv6.
    The questions do not assume that multihoming is the only problem of
    interest, nor do they demand a more general solution either.

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1. Introduction

    At the time of this writing there are some six separate solutions
    looking at the problem of multihoming within IPv6 and related
    problems, such as the locator/identifier split.

    In order to sort through how proposed solutions compare against one
    another, and potentially, how they can borrow mechanisms and design
    decisions from one another, this document contains a list of pointed

    The purpose of these questions is to focus people who propose
    solutions on practical operational problems that both single-homed
    and multi-homed deployments may face.

    Unless it is blatantly obvious, each question contains some reasoning
    as to why it is being asked.  It is envisioned that no solution will
    answer every question with completeness, but that there will be
    tradeoffs to be made.  The answers by the various designers of
    solutions will hopefully shed some light on which tradeoffs we as a
    community wish to make.

    It would seem silly for people who have written out detailed answers
    to these questions to have to repeat the exercise. Therefore, a
    simple reference to existing documents will suffice, so long as the
    answer is complete.  If it is not complete, then feel free to
    reference it and add what text is necessary to make the answer

    This document presumes a familiarity with RFC 3582 [2], and does not
    attempt to repeat the requirements work gathered there.

1.1 Differences between -02 and -03

    Added questions relating to whether existing communications can be
    piggybacked.  Added questions about how the mechanism aggregates if
    site-wide, or how information is gotten by parties if per-host.
    Several other additions.

1.2 Differences between -01 and -02

    Security Considerations and a touchup in some of the words.

1.3 Differences between -00 and -01

    In section, address whether rendezvous SHOULD be handled in a

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    In section 2.2.3, clarified wording.

    New subsection 2.4.3 on what if you do not use DNS

    new subsections  2.3,4, 2.4.7, 2.4.8, 2.4.9, 2.4.14

    Clarifications on 2.4.15, and perhaps elsewhere.

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2. The Questions

2.1 Routing

2.1.1 How will your solution solve the multihoming problem?

    That's why we're here.  Remember, a reference is fine.

2.1.2 Uniqueness Does your solution address mobility?

    If so, how are rendezvous handled?  Can your solution handle both
    locators changing at the same time?  If so, please explain. Should
    it?  If not, how will your solution interact with MOBILEIP-V6 [3]

2.2 Identifiers and locators

2.2.1 Does your solution provide for a split between identifiers and

2.2.2 What is the lifetime of a binding from an identifier to a locator?

2.2.3 How is the binding updated?

    Will transport connections remain up when new paths become available
    or when old ones become unavailable?  How does the end node discover
    these events?

2.3 On The Wire

2.3.1 At what layer is your solution applied, and how?

    Is it applied in every packet?  If so, what fields are used?

2.3.2 Why is the layer you chose the correct one?

    Each layer has its benefits and tradeoffs.  For instance, transport
    layer solutions would require that EVERY transport be modified, while
    IP layer solutions may entail expansion of the packet or a change to
    the pseudo-header (thus requiring changes to the transport layer).

2.3.3 Can your solution be aggregated and implemented site-wide?

    Some mechanisms may be implemented per host.  Others may be
    implemented at the site level.  If yours is implemented site-wide
    does it aggregate well?  If your solution is implemented at the host

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    level, how is necessary information gotten to the relevant parties of
    the communication?

2.3.4 Does your solution impact existing traffic engineering methods,
       such as MPLS-TE?

    Traffic engineering allows for source-based traffic aggregation to a
    particular destination.  How will your mechanism interact with such
    existing methods?

2.3.5 Does your solution expand the size of an IP packet?

    Expanding the size of an IP packet may cause excessive fragmentation
    in some circumstances.

2.3.6 Will your solution add additional latency?

    Latency is an important factor in many applications, including voice.
    Any substantial amount of additional latency, including session
    initiation would be highly undesirable.

2.3.7 Can multihoming capabilies be negotiated end to end during a

    If the proposal introduces additional overhead, can the information
    be somehow piggybacked on messages that are already used?  This would
    be useful in order to keep connection setup constant.  Please also
    indicate any drawbacks that might apply due to this piggybacking.

2.3.8 Do you change the way fragmenting is handled?

    If you use a shim approach, do you fragment above or below the shim?
    How are fragments identified, so that they can be reassembled?  If
    you use any additional names, do they need to be associated with
    fragments?  If not, why not?  If so, how will that happen?

2.3.9 Are there any changes to ICMP error semantics?

    Do you create new codes?  If so, why and what do they mean? Will a
    host that is not aware of your scheme see them?

2.4 Names, Hosts, Endpoints, or none of the above?

2.4.1 Please explain the relationship of your solution to DNS

    If your solution uses new names for identifiers, please explain what
    mappings are defined, and how they are performed?

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    If there are any additional administrative requirements, such as new
    zones or RR types to manage, please explain them as well.

2.4.2 If you have separate locators and identifiers, how will they be

    Does the mapping work in both directions?  How would someone
    debugging a network determine which end stations are involved?

2.4.3 If you are not using DNS...

    Please describe the mechanism you are using. Please describe authentication/authorization

    How are bindings authenticated and authorized. What technology do you
    build on for this mechanism? Is your mechanism hierarchical?

    Please describe the hierarchical breakdown.

2.4.4 Please explain interactions with "2-faced" DNS

    2-faced DNS is used so that hosts behind a NAT get one address for
    internal hosts, while hosts outside the NAT get another. Similar
    mechanisms are used for application layer gateways, such as SOCKS

2.4.5 Does your solution require centralized registration?

    For instance, if you are using the DNS, what will be the top level
    domain, and how will the name space distribute through it?

    Also, how will the centralized registration be managed?

2.4.6 Have you checked for DNS circular dependencies?

    If you are using the DNS in your solution, is it required for
    connectivity?  What happens if the DNS fails?  Can communication
    between the DNS resolver and the server make use of your solution?
    What about between the application and the resolver?

2.4.7 How does a host know its identity?

    If you are establishing a new identity, how does the host learn it?

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2.4.8 What if a DNS server itself is multihomed?

    If a link fails or a service is dropped, how will it impact DNS?
    Again are there any dependency loops?  Perhaps diagram out your
    dependencies to make sure.

2.4.9 What additional load will be placed on DNS servers?

    Can the load be distributed?  Remember that DNS is optomized for READ

2.4.10 Any upstream provider support required?

    If so, please describe.

2.4.11 What application/API changes are needed?

    Will old code just work with the new mechanism? For instance, what
    about code that uses gethostbyname()?

    Will getaddrinfo() need to change?

    What about other API calls?

2.4.12 Is this solution backward compatable with "old" IP version 6?

    Can it be deployed incrementally?  Please describe how.

    Does your solution impose requirements on non-multihomed/non-mobile

    What happens if someone plugs in a normal IPv6 node?

2.4.13 Is your solution backward compatable with IPv4?

    How will your mechanism interact with 6to4 gateways and IPv4 hosts?

2.4.14 Can IPv4 devices take advantage of this solution?

    Can the same mechanism somehow be used on the existing network?  N.B.
    this is NOT a requirement, but more a consideration.

2.4.15 What is the impact of your solution on different types of sites?

    How are single homed sites impacted?

    How are small multihomed sites impacted?

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    How does it scale for large multihomed sites?

    What about ad-hoc sites such as an IETF event?

2.4.16 How will your solution interact with other middleboxes?

    What are the implications for firewalls?  What are the interactions
    with NAT?  What are the interactions with web caches? What
    complications are introduced with your solution?  For instance, are
    there implication for ingress filters?  If so, what are they?

2.4.17 Are there any implications for scoped addressing?

    Please see RFC 3513 [1].  How does your mechanism interact with

    How does your solution interact with link-local addressing

    How does your solution interact with Son-Of-Sitelocal (whatever that
    will be)?

2.4.18 Are there any layer 2 implications to your proposal?

    While Ipv6 has a simplified approach to layer 2, perhaps you
    unsimplifiied it.  If so, please provide details.

2.4.19 Referrals

    How will your solution handle referrals, such as those within FTP?

    It must be possible for existing applications to continue to work.
    Referrals exist within various other protocols, such as so-called
    "peer to peer" applications.

2.4.20 What new information should applications be aware of?

    If there are new bindings, what does the application need to take
    advantage of them?  How does the application present a

2.5 Legal Stuff

    Are you introducing a namespace that might involve mnemonics? Doing
    so might introduce trademark concerns.  If so, how do you plan to
    address such concerns?

    Are there any organizations required to manage a new name space? If
    so, please describe what they are and how the method will scale.

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3. Security Considerations

    How secure should a multi6 solution be?  This is a reasonable
    question for each solution to answer.  The author opines that the
    worst case should be no worse than what we have today.  For example,
    would a multi6 solution open up a host on either end of a
    communication to a time-based attack?  Any such risks should be
    clearly stated by the authors.  Considerable time should be spent on
    threat analysis. Please see [4] for more details.

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4. Acknowledgments

    The author wishes to acknoledge everyone in the multi6 group and
    elsewhere that is putting forward proposals.  It is easy to ask
    questions like the ones found in this draft.  It is quite a bit
    harder to develop running code to answer them.  Marcelo Bagnulo, Kurt
    Erik Lindqvist, Patrik Faltstrom, Brian Carpenter, and Iljitsch van
    Beijnim provided input to this document.

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Normative References

    [1]  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
         Addressing Architecture", RFC 3513, April 2003.

    [2]  Abley, J., Black, B. and V. Gill, "Goals for IPv6
         Site-Multihoming Architectures", RFC 3582, August 2003.

    [3]  Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
         IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), July

    [4]  Nordmark, E. and T. Li, "Threats relating to IPv6 multihoming
         solutions", draft-nordmark-multi6-threats-00 (work in progress),
         October 2003.

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Informative References

    [5]  Kitamura, H., "A SOCKS-based IPv6/IPv4 Gateway Mechanism", RFC
         3089, April 2001.

Author's Address

    Eliot Lear
    Cisco Systems
    170 W. Tasman Dr.
    San Jose, CA  95134-1706

    EMail: lear@cisco.com

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