Network Working Group E. Lear
Request for Comments: 4219 Cisco Systems
Category: Informational October 2005
Things Multihoming in IPv6 (MULTI6) Developers Should Think About
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
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.
Table of Contents
1. Introduction ....................................................3
1.1. Reading this Document ......................................3
2. On the Wire Behavior ............................................4
2.1. How will your solution solve the multihoming problem? ......4
2.2. At what layer is your solution applied, and how? ...........4
2.3. Why is the layer you chose the correct one? ................4
2.4. Does your solution address mobility? .......................4
2.5. Does your solution expand the size of an IP packet? ........4
2.6. Will your solution add additional latency? .................4
2.7. Can multihoming capabilities be negotiated
end-to-end during a ........................................4
2.8. Do you change the way fragmenting is handled? ..............5
2.9. Are there any layer 2 implications to your proposal? .......5
3. Identifiers and Locators ........................................5
3.1. Uniqueness .................................................5
3.2. Does your solution provide for a split between
identifiers and ............................................5
3.3. What is the lifetime of a binding from an
identifier to a locator? ...................................5
3.4. How is the binding updated? ................................5
3.5. How does a host know its identity? .........................5
3.6. Can a host have multiple identifiers? ......................5
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3.7. If you have separate locators and identifiers, how
will they be ...............................................5
3.8. Does your solution create an alternate "DNS-like"
service? ...................................................5
3.9. Please describe authentication/authorization ...............6
3.10. Is your mechanism hierarchical? ...........................6
3.11. Middlebox interactions ....................................6
3.12. Are there any implications for scoped addressing? .........6
4. Routing System Interactions .....................................6
4.1. Does your solution change existing aggregation methods? ....6
4.2. Does the solution solve traffic engineering requirements? ..7
4.3. Does the solution offer ways for the site to manage
its traffic ................................................7
4.4. If you introduce any new name spaces, do they
require aggregation? .......................................7
4.5. Does your solution interact with Autonomous System
numbering? .................................................7
4.6. Are there any changes to ICMP error semantics? .............7
5. Name Service Interactions .......................................7
5.1. Please explain the relationship of your solution to DNS ....7
5.2. Please explain interactions with "2-faced" DNS .............7
5.3. Does your solution require centralized registration? .......8
5.4. Have you checked for DNS circular dependencies? ............8
5.5. What if a DNS server itself is multihomed? .................8
5.6. What additional load will be placed on DNS servers? ........8
5.7. Any upstream provider support required? ....................8
5.8. How do you debug connectivity? .............................8
6. Application Concerns and Backward Compatibility .................8
6.1. What application/API changes are needed? ...................8
6.2. Is this solution backward compatible with "old" IP
version 6? .................................................9
6.3. Is your solution backward compatible with IPv4? ............9
6.4. Can IPv4 devices take advantage of this solution? ..........9
6.5. What is the impact of your solution on different
types of sites? ............................................9
6.6. How will your solution interact with other middleboxes? ...10
6.7. Referrals .................................................10
6.8. Demonstrate use with a real life complex application ......10
7. Legal Concerns .................................................10
8. Security Considerations ........................................10
9. Acknowledgements ...............................................11
10. References ....................................................11
10.1. Normative References .....................................11
10.2. Informative References ...................................11
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1. Introduction
At the time of this writing there are quite a number of proposed
solutions to the problem of multihoming within IPv6, and related
problems such as the locator/identifier split.
This document contains several sets of questions that attempt to
focus these solutions on operational problems. This document does
not suggest methods to solve the problem. Rather, we simply want to
ensure that while solving a problem the medicine is not worse than
the cure. We focus on practical operational problems that both
single-homed and multihomed deployments may face.
It is the hope of the author that perhaps the authors of other
proposed solutions will use this document to identify gaps in their
solutions, and cooperate to close those gaps.
1.1. Reading this Document
The questions are organized along the following lines:
o changes to on the wire behavior;
o routing system interactions;
o identifier/mapping split;
o application concerns and backward compatibility;
o name service interactions;
o legal concerns; and
o security considerations.
In reality many questions cut across all of these concerns. For
instance, the identifier / locator split has substantial application
implications, and every area has security considerations.
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 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.
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RFC 4219 MULTI6 Solution Questionnaire October 2005
2. On the Wire Behavior
2.1. How will your solution solve the multihoming problem?
Please scope the problem you are attempting to solve and what you are
not attempting to solve.
2.2. At what layer is your solution applied, and how?
Is it applied in every packet? If so, what fields are used?
2.3. 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).
2.4. 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)
2.5. Does your solution expand the size of an IP packet?
Expanding the size of an IP packet may cause excessive fragmentation
in some circumstances.
2.6. 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.
2.7. Can multihoming capabilities 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.
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2.8. 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?
2.9. Are there any layer 2 implications to your proposal?
While IPv6 has a simplified approach to layer 2, perhaps you
unsimplified it. If so, please provide details.
3. Identifiers and Locators
3.1. Uniqueness
3.2. Does your solution provide for a split between identifiers and
locators?
3.3. What is the lifetime of a binding from an identifier to a locator?
3.4. 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?
3.5. How does a host know its identity?
If you are establishing a new identity, how does the host learn it?
3.6. Can a host have multiple identifiers?
If so, how does an application choose an identity?
3.7. 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?
3.8. Does your solution create an alternate "DNS-like" service?
If you use mechanisms other than DNS, first, why was DNS not
appropriate? Also, how will this other mechanism interact with DNS?
What are its scaling properties?
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3.9. Please describe authentication/authorization
How are bindings authenticated and authorized. What technology do
you build on for this mechanism?
3.10. Is your mechanism hierarchical?
Please describe the hierarchical breakdown.
3.11. Middlebox interactions
What are the implications for firewalls? What are the interactions
with Network Address Translation (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?
When considering this question, there are really two issues. First,
will middleboxes impede your solution by rewriting headers in some
way, as NATs do for IP addresses, and web caches do at higher layers?
Second, is there a way in which middleboxes are actually part of your
solution? In particular, are they required? This would be the case,
for example, with Generalized Structure Element (GSE) (8+8).
3.12. 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)?
4. Routing System Interactions
4.1. Does your solution change existing aggregation methods?
Routing on the Internet scales today because hosts and networks can
be aggregated into a relatively small number of entries. Does your
solution change the way in which route aggregation occurs?
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4.2. Does the solution solve traffic engineering requirements?
One of the significant goals of IPv4 multihoming solutions has been
the ability to perform traffic engineering based on appropriately
adjusting the BGP advertisements. If the prefixes used by such sites
was be aggregated (particularly beyond the site"s border), the site"s
ability to perform traffic engineering would be diminished.
4.3. Does the solution offer ways for the site to manage its traffic
flows?
If so, how? Is this controllable on a per-host basis, or on a
per-site basis?
4.4. If you introduce any new name spaces, do they require aggregation?
Is it desirable or required that, in order to scale distribution of
any mapping information, an aggregation method be introduced?
4.5. Does your solution interact with Autonomous System numbering?
If your solution involves address prefixes distributed using BGP4+,
does it interact with the use of AS numbers and, if so, how? Will it
require additional AS numbers?
4.6. 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?
5. Name Service Interactions
5.1. 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?
If there are any additional administrative requirements, such as new
zones or RR types to manage, please explain them as well.
5.2. 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].
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5.3. 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?
5.4. 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?
5.5. 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.
5.6. What additional load will be placed on DNS servers?
Can the load be distributed? Remember that DNS is optimized for READ
operations.
5.7. Any upstream provider support required?
If so, please describe. For instance, currently reverse mappings are
delegated down from upstream providers. How would this work with
your solution?
5.8. How do you debug connectivity?
How would tools like ping and traceroute need to be enhanced? What
additional tools would prove useful or necessary? For instance, if
there is an id/locator split, can one ping an identifier? If so,
what gets returned?
6. Application Concerns and Backward Compatibility
6.1. What application/API changes are needed?
Will old code work with the new mechanism? For instance, what about
code that uses gethostbyname()?
Will getaddrinfo() need to change?
What about other API calls?
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There are several possible approaches. For instance, a multihoming
service could attempt to require no changes to the API, in which case
it is possible that IP addresses might become opaque blobs that work
with the API, but might break operational assumptions that
applications make about addresses. Consider the case of a web server
that wants to log IP addresses. How will it accomplish this task?
Another approach is to have some sort of compatibility library for
legacy applications, but also provide a richer calling interface for
transparency.
Yet another approach would be to only provide the new functionality
to those applications that make use of a new calling interface.
One useful exercise would be to provide code fragments that
demonstrate any API changes.
6.2. Is this solution backward compatible 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?
6.3. Is your solution backward compatible with IPv4?
How will your mechanism interact with 6to4 gateways and IPv4 hosts?
6.4. 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 primary consideration, but perhaps a side benefit of a
particular solution.
6.5. What is the impact of your solution on different types of sites?
What will the impact of your solution be on the following types of
systems?
o single homed sites
o small multihomed sites
o large multihomed sites
o ad-hoc sites
o short lived connections (think aggregator wireless ISPs)
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RFC 4219 MULTI6 Solution Questionnaire October 2005
In particular, consider ongoing administration, renumbering events,
and mobile work forces.
6.6. How will your solution interact with other middleboxes?
6.7. Referrals
How will your solution handle referrals, such as those within FTP or
various conferencing or other peer to peer systems?
Referrals exist within various other protocols, such as so-called
"peer to peer" applications. Note that referrals might suffer three
types of failure:
firewall and NAT - Is there failure just as what FTP active mode
experiences today with relatively simple firewalls?
time-based - Is there something ephemeral about the nature of the
solution that might cause a referral (such as a URL) to fail over
time, more so than what we have today?
location-based - If the binding varies based on where the parties are
in the network, and if one moves, will they no longer be able to
find each other?
6.8. Demonstrate use with a real life complex application
Provide a detailed walk-through of SIP + Real Time Streaming Protocol
(SIP+RTSP) when one or several of the peers are multihomed. How does
your analysis change when encrypted RTSP is used or when SIP with
S/MIME end-to-end (e2e) signalling is used?
7. Legal Concerns
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.
8. 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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As IP addresses can often be tied to individuals, are there any
auditing or privacy concerns introduced by your solution?
9. Acknowledgements
The author wishes to acknowledge everyone in the multi6 group and
elsewhere that is putting forward proposals. It is easy to ask
questions like the ones found in this document. It is quite a bit
harder to develop running code to answer them. Marcelo Bagnulo, Kurt
Erik Lindqvist, Joe Touch, Patrik Faltstrom, Brian Carpenter, and
Iljitsch van Beijnum provided input to this document.
10. References
10.1. 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", RFC 3775, June 2004.
[4] Nordmark, E., "Threats Relating to IPv6 Multihoming Solutions",
RFC 4218, October 2005.
10.2. Informative References
[5] Kitamura, H., "A SOCKS-based IPv6/IPv4 Gateway Mechanism",
RFC 3089, April 2001.
Author's Address
Eliot Lear
Cisco Systems GmbH
Glatt-com, 2nd Floor
CH-8301 Glattzentrum ZH
Switzerland
EMail: lear@cisco.com
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