Network Working Group E. Lear
Internet-Draft Cisco Systems
Expires: November 22, 2004 May 24, 2004
Things MULTI6 Developers should think about
draft-lear-multi6-things-to-think-about-03
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
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
questions.
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
complete.
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 2.1.2.1, address whether rendezvous SHOULD be handled in a
solution.
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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
2.1.2.1 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]
(MIPv6)
2.2 Identifiers and locators
2.2.1 Does your solution provide for a split between identifiers and
locators?
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
connection?
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
mapped?
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.
2.4.3.1 Please describe authentication/authorization
How are bindings authenticated and authorized. What technology do you
build on for this mechanism?
2.4.3.2 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
[5].
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
operations.
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
hosts?
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
multicast?
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
&dquot;connection&dquot;?
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
2003.
[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
US
EMail: lear@cisco.com
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