IPv6 Maintenance Working Group A. Matsumoto
Internet-Draft T. Fujisaki
Intended status: Informational NTT
Expires: September 9, 2010 R. Hiromi
Intec Netcore
March 8, 2010
Solution approaches for address-selection problems
draft-ietf-6man-addr-select-sol-03.txt
Abstract
In response to address selection problem statement and requirement
documents, this document describes solution approaches and evaluates
proposed solution mechanisms in line with requirements. It also
examines the applicability for each solution mechanism, and concludes
that no single solution solves the problems and the combination of
the solutions should be the way forward.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Solution Approaches . . . . . . . . . . . . . . . . . . . . . 4
2.1. Proactive approach . . . . . . . . . . . . . . . . . . . . 4
2.2. Reactive approach . . . . . . . . . . . . . . . . . . . . 4
3. Solution Mechanisms . . . . . . . . . . . . . . . . . . . . . 4
3.1. Policy Distribution (Proactive Approach) . . . . . . . . . 5
3.1.1. Requirements correspondence analysis . . . . . . . . . 5
3.1.2. Other issues . . . . . . . . . . . . . . . . . . . . . 6
3.2. Routing system assistance (Proactive Approach) . . . . . . 6
3.2.1. Requirements correspondence analysis . . . . . . . . . 7
3.2.2. Other issues . . . . . . . . . . . . . . . . . . . . . 8
3.3. Trial-and-error based (Reactive Approach) . . . . . . . . 8
3.3.1. Requirement correspondence analysis . . . . . . . . . 8
3.3.2. Other issues . . . . . . . . . . . . . . . . . . . . . 10
3.4. All at once (Reactive Approach) . . . . . . . . . . . . . 10
3.4.1. Requirement correspondence analysis . . . . . . . . . 10
3.4.2. Other issues . . . . . . . . . . . . . . . . . . . . . 12
4. Applicability Comparison . . . . . . . . . . . . . . . . . . . 12
4.1. Dynamic-static and managed-unmanaged . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Other Solutions . . . . . . . . . . . . . . . . . . . 16
Appendix B. Revision History . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
Today, the RFC 3484 mechanism is widely implemented in major OSs.
However, many people, including us, have found that in many sites the
default address selection rules do not work perfectly. RFC 5220
[RFC5220] lists problematic cases that resulted from incorrect
address selection. RFC 5221 [RFC5221] enumerates requirements for
address-selection mechanisms.
In the IETF mailing lists and in the internet-draft archives, some
mechanisms for solving address-selection problems were proposed.
This document describes possible design approaches for solving
address selection problems. After summarizing each existing proposal
mechanism and analyzing how well the method corresponds with the
requirements, applicability domain for each mechanism are evaluated.
2. Solution Approaches
There are two types of approaches that can control the behavior of
hosts in terms of the selection of destination address and source
address. The first type is proactive, where the host is given the
necessary information to decide the destination and source addresses
before the beginning of data transmission. The other type is
reactive, where the host decides appropriate destination address and
source addresses through trial and error.
2.1. Proactive approach
In this approach, hosts should have all or a part of the information
for selecting appropriate address pair before the actual data
transmission.
2.2. Reactive approach
In this approach, the host does not have initial information for
address selection. It will try using different pairs of destination
and source addresses until the connection is established. It can
take advantage of error messages, and can make use of it to prune
unworkable pair of addresses.
3. Solution Mechanisms
This section describes the evaluation of the four mechanisms. The
evaluation value has a 3-point scale for each of 8 requirements in
the requirement document. The meanings of the points are as follows.
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1 : bad
2 : fair
3 : good
About "Effectiveness", the score is 1 if the approach solves no
problematic cases described in the problem statement document, 2 if
it can handle at least one, and 3 if it solves every case.
3.1. Policy Distribution (Proactive Approach)
In this approach, a host obtains everything, usually policies, needed
to select addresses prior to communication. The address selection
design team is working on this approach.
[I-D.ietf-6man-addr-select-considerations] DHCPv6 and RA are possible
transport protocols. There is a proposal document
[I-D.fujisaki-dhc-addr-select-opt] in which DHCPv6 is used for this
purpose.
This approach can take advantage of the RFC 3484 Policy Table, which
is already widely deployed. By distributing policies for the Policy
Table, you can auto-configure a host's address selection behavior.
3.1.1. Requirements correspondence analysis
1. Effectiveness: 3
It can support all cases by using the policy table.
2. Timing: 3
All information for communication is in a host in advance.
Communication starts at once when it is necessary and the
communication process refers to local policy information, which
does not cause any delay or incorrect address selection.
3. Dynamic update: 3
Though it depends on what protocol is used to distribute the
policies, some mechanisms support information updates from the
server, such as RA and DHCPv6 RECONFIGURE.
4. Node-specific behavior: 3
For distribution to individual hosts in the same segment, DHCPv6
and unicast based RA can be used.
5. Application-specific behavior: 2
The policy table itself doesn't support application-specific
address selection. It can be done using the address selection
API. [RFC5014]
6. Multiple interfaces: 2
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If all interfaces belong to the same administration domain, it is
possible for the address-selection information to be controlled by
administrators of that domain. However, if not, routing
information and address selection policies are not always
equivalent between domains. For such cases, the algorithm for
merging policies have to be considered, which is documented in
this document. [I-D.arifumi-6man-addr-select-conflict]
7. Central control: 3
It can support central control. A site administrator or a service
provider can determine users' policy tables.
8. Route selection: 2
Current solutions, such as DHCPv6 and RA, do not have a mechanism
for cooperation with routing protocols. This could be done with
other techniques such as "source address based routing" or
"Default Router Preferences and More-Specific Routes" RFC 4191.
[RFC4191]
9. Compatibility with RFC 3493: 3
This approach is able to coexist with any kind of applications
(socket API). In detail, any types of function such as
getaddrinfo(), getsockname(), connect() or other typical system
calls will work without alterations if this mechanism is applied
to a host.
10. Compatibility and Interoperability with RFC 3484: 3
The basic idea of this approach has a compatibility with RFC3484.
This approach make RFC3484 policy table configurable to put some
hints related with it's individual network case.
11. Security: 2
By injecting address selection policy, a session hijacking can be
possible in this mechanism. A combination of Layer 2 securing
techniques and this mechanism will be able to be effective against
security concerns. DHCP and RA protocol have own security
measures and they also protect from them.
3.1.2. Other issues
None.
3.2. Routing system assistance (Proactive Approach)
Fred Baker proposed this approach. A host asks the DMZ routers or
the local router which is the best pair of source and destination
addresses when the host has a set of addresses A and the destination
host has a set of addresses B. Then, the host uses the policy
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provided by the server/routing system as a guide in applying the
response.
3.2.1. Requirements correspondence analysis
1. Effectiveness: 3
A routing system knows about information about paths toward the
destination and information about which of their prefixes should
be used. Therefore, it is possible to select an appropriate pair
of source and destination addresses.
2. Timing: 3
A routing system always has up-to-date routing information, so it
will be possible to provide suitable information whenever requests
come.
3. Dynamic update: 3
A routing system always has up-to-date routing information, and it
will be possible to provide suitable information whenever requests
come.
4. Node-specific behavior: 3
Node-specific information can be provided if a server recognizes
individual nodes.
5. Application-specific behavior: 2
A routing system does not care about applications. Using address
selection API allows nodes to behave in an application-specific
way.
6. Multiple Interfaces: 2
The same as the policy based mechanism.
7. Central Control: 3
It is possible to provide address selection information from one
source.
8. Route Selection: 3
It is possible to give next-hop selection advice to a host. As
routers have routing information, it would seem to be easier for
routers to implement this function.
9. Compatibility with RFC 3493: 1
In the existing TCP/IP protocol stack implementation, destination
address selection is mainly the role of the application and not
that of the kernel unlike source address selection. Therefore,
implementing this model without affecting applications is not
feasible.
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10. Compatibility and Interoperability with RFC 3484: 2<
Currently it just proposed and there is no implementation.
Therefore, it depends on how to implement with this requirement,
but it can be coexist with RFC3484.
11. Security: 2
This approach has a weakness on hijacking just like the previous
mechanism.
3.2.2. Other issues
- It has a possible scalability problem. A host must consult the
routing system every time it starts a connection if the host does
not have address selection information for the destination host or
if the information lifetime has expired.
- The existing host/router OS implementation must be changed a lot.
This can be problematic in some cases.
3.3. Trial-and-error based (Reactive Approach)
M. Bagnulo presented a new address selection idea in his draft.
Hirotaka Matsuoka extended and elaborated this approach in his draft.
[I-D.matsuoka-multihoming-try-and-error] When the host notices that a
network failure has occurred or packets have been dropped somewhere
in the network by, for example, an ingress filter, the host stores a
negative cache of address selection.
Hosts may use some kinds of error messages, e.g, ICMP error messages,
from a network to detect that sent packets did not reach the
destination quickly.
The host stores a cache of address selection information so that the
host can select an appropriate source address for new connections.
3.3.1. Requirement correspondence analysis
1. Effectiveness: 2
This solution is not effective for the destination address
selection cases, such as a problem about IPv4 or IPv6
prioritization described in the problem statement document.
2. Timing: 1
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Hosts should try to use all the available source addresses to the
maximum to find an appropriate source address. If the host tries
the next source address after the previous trial using another
source address has failed, it may take a long time because this
trial-and-error process lasts until the connection succeeds. If
the host does not use an error message from a network to detect a
connection error, it takes longer to wait for a time-out. This
issue largely depends on the cacue functionality, but there is no
established algorithm for this.
3. Dynamic update: 3
If hosts detect a connection failure using some reliable
mechanism, such like TCP or ICMP error messages, a connection
failure caused by some changes in the network will be detected
immediately by the hosts.
4. Node-specific behavior: 2
This solution does not have a function for node-specific behavior.
However, it is not impossible to implement by deploying a packet
filter configured for each node at the gateways through which the
packets from nodes pass.
5. Application-specific behavior: 2
This solution does not have a function for application-specific
behavior. However, the mechanism of this approach does not
exclude address selection by each application.
6. Multiple interfaces: 3
If the protocol-stack or an application supports interface
selection and it tries to establish a connection by changing
addresses and also interfaces, it can find a working combination
of addresses and interface.
7. Central control: 2
The only way that a central administrator has to control the node
behavior is switching a filter on/off on the network. Therefore,
advanced control such as traffic engineering and QoS is almost
impossible.
8. Route Selection: 2
This solution does not refer to next-hop selection for the
transmission of a packet. So, it should be used with some routing
function such as RFC 4191 on the nodes.
9. Compatibility with RFC 3493: 1
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This approach has possibility to interfere with coexistence with
applications(socket APIs). The returen value of functions would
be changed for its meaning. A case is suspected that the return
value of connect() system call will change its state from "non-
blocking" to "blocking" and this will bring alteration to the
application behaviours. Because of this suspicion, this approach
scores 1.
10. Compatibility and Interoperability with RFC 3484: 2
It depends on how to implement with this requirement. But there
will be possible conflict which a result will be overwrite the
3484 policy table without any permission of domain administrators.
11. Security: 1
This approach has a weakness on hijacking. Moreover, it may
expose the privacy of the user host by showing all or a part of
the addresses of the host to the destination host.
3.3.2. Other issues
- A host must learn address selection information for each
destination host. Therefore, the number of cache entries could be
very large.
- The existing host/router OS implementation must be changed a lot.
In particular, changing the source address of the existing
connection is not so easy and has a big impact on the existing
TCP/IP protocol stack implementation.
3.4. All at once (Reactive Approach)
This is another proposal by Fred Baker at 6man ML. By trying all the
pairs of source and destination addresses at once, or in a very shord
period of time, a connection can be established as far as there is at
least one working pair of addresses.
This mechiansm can easily combined with the error message retrieval
and cache function discussed in Section 3.3 to prune the unnecessary
connection trials.
3.4.1. Requirement correspondence analysis
1. Effectiveness: 2
This solution is not effective for the destination address
selection cases, such as a problem about IPv4 or IPv6
prioritization described in the problem statement document.
2. Timing: 3
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The user does not have to wait for extra period of time.
3. Dynamic update: 3
It can reflect dynamically changing network, as far as it always
tries all possible addresses and next-hops.
4. Node-specific behavior: 2
This solution does not have a function for node-specific behavior.
However, it is not impossible to implement by setting a packet
filter for each node on the gateways through which the packets
from nodes pass.
5. Application-specific behavior: 2
This solution does not have a function for application-specific
behavior. However, the mechanism of this approach does not
exclude address selection by each application.
6. Multiple interfaces: 3
If the protocol-stack supports interface selection and it tries to
establish a connection by changing addresses and also interfaces,
it can find a working combination of addresses and interface.
But, in such a environment, a host has to try all the combinations
of source address, destination address, and next-hop addresses,
which can be huge amount of connection establishment trial.
7. Central control: 2
The only way that a central administrator has to control the node
behavior is switching a filter on/off on the network. Therefore,
advanced control such as traffic engineering and QoS is almost
impossible.
8. Route Selection: 2
This solution does not refer to next-hop selection for the
transmission of a packet. Therefore, it should be used with some
routing function such as RFC 4191 on the nodes.
9. Compatibility with RFC 3493: 1
For non-connected transport protocols, there is no universal nor
established way of telling a connection is successful or failure
from the viewpoint of anything other than the application. In
this sense, it does not work for non-connected transport
protocols.
10. Compatibility and Interoperability with RFC 3484: 1
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This mechanism uses every possible addresses for its rather
initial connection setup. In that sense, it does not follow the
address selection rules of RFC 3484.
11. Security: 1
This approach has a weakness on hijacking. Moreover, it may
expose the privacy of the user host by showing all or a part of
the addresses of the host to the destination host.
3.4.2. Other issues
- It brings unnecessary traffic to network, host, routers, and
destinations.
- It breaks DNS round robin based load balancing.
- A host must learn address selection information for each
destination host. Therefore, the number of cache entries can be
very large.
- The existing host OS implementation must be changed significantly.
4. Applicability Comparison
If you actually want to choose one mechanism to solve your address
selection problem, it is important to figure out which approach is
best suited to your situation. This section tries to evaluate the
applicability of each approach from several aspects.
4.1. Dynamic-static and managed-unmanaged
We use two axes to evaluate the applicability of the four approaches.
One axis shows whether or not the network structure changes
dynamically and the other axis shows whether the site is managed or
unmanaged. In a managed network, by our definition, a network
administrator manages his or her network, routers, and hosts. For
example, an enterprise network is managed, whereas a home network and
a SOHO network are unmanaged.
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static dynamic
<-------------------------------------------->
unmanaged ^ +----------+ +---------------------------+
| | | +-+--------------+ all-at-once|
| | | | | | |
| | +--+-+-+------------+ | |
| | | | | | | | |
| | | | | | | | |
| | | | | +------------+-+------------+
| | | | | try-error| |
| | +--+-+--------------+ |
| | | | |
| | | | |
| | Policy | | RouterAssist |
| | Dist | | |
| | | | |
| +----------+ +----------------+
managed v
PolicyDist:
- In a dynamic site, the policy table must be updated accordingly
and traffic for policy table distribution increases.
try-and-error:
- This is a slightly manageable than all-at-once in that it does not
change the paths of established connections dynamically.
- In a very dynamic site, the use of an address selection
information cache does not have a good effect. This results in
connection failure and may degrade usability badly.
- Even in a very static site, a host may try inappropriate addresses
or next-hops and experience connection failures.
RouterAssist:
- A host must send at least as many queries as the number
destination hosts. Therefore, in a static site, this method is
not optimal.
- In a very dynamic site, address selection information cache is no
help. If the cache function is not used, then connection failures
do not occur.
all-at-once:
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- In a static site, all-at-once is not desirable because of its
connection sequence overhead and timeout-wait for path
exploration.
- In a managed site, it is not easy to manage in terms of node-
specific address selection control and central control.
5. Security Considerations
Incorrect address selection can lead to serious security problems,
such as session hijacking. However, we should note that address-
selection is ultimately decided by nodes and their users. There are
no means to enforce a specific address-selection behavior upon every
end-host from outside the host. Therefore, a network administrator
must take countermeasures against unexpected address selection.
6. IANA Considerations
This document has no actions for IANA.
7. Conclusions
In this document, we examined solutions to address selection problems
in the IPv6 multi-prefix environment. From the requirement analysis
and applicability evaluation, it can be concluded that there is no
one perfect solution for this series of problems.
Hence, we have to combine two or more solutions together. The design
team proposal and all-at-once proposal are extreme opposite, and
combining these two seems to make the coverage biggest problem
spaces.
8. References
8.1. Normative References
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in Multi-
Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008.
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[RFC5221] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Requirements for Address Selection Mechanisms", RFC 5221,
July 2008.
8.2. Informative References
[I-D.arifumi-6man-addr-select-conflict]
Matsumoto, A., Fujisaki, T., and R. Hiromi,
"Considerations of address selection policy conflicts",
draft-arifumi-6man-addr-select-conflict-01 (work in
progress), October 2009.
[I-D.axu-addr-sel]
Suhonen, A., "Address Selection Using Source Address
Specific Routing Tables", draft-axu-addr-sel-00 (work in
progress), July 2009.
[I-D.fujisaki-dhc-addr-select-opt]
Fujisaki, T., Matsumoto, A., and R. Hiromi, "Distributing
Address Selection Policy using DHCPv6",
draft-fujisaki-dhc-addr-select-opt-09 (work in progress),
March 2010.
[I-D.ietf-6man-addr-select-considerations]
Chown, T., "Considerations for IPv6 Address Selection
Policy Changes",
draft-ietf-6man-addr-select-considerations-00 (work in
progress), October 2009.
[I-D.ietf-shim6-multihome-shim-api]
Komu, M., Bagnulo, M., Slavov, K., and S. Sugimoto,
"Socket Application Program Interface (API) for
Multihoming Shim", draft-ietf-shim6-multihome-shim-api-13
(work in progress), February 2010.
[I-D.matsuoka-multihoming-try-and-error]
Matsuoka, H., "A Try and Error type approach for
multihoming", draft-matsuoka-multihoming-try-and-error-00
(work in progress), April 2009.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
Socket API for Source Address Selection", RFC 5014,
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September 2007.
[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, June 2009.
[RFC5534] Arkko, J. and I. van Beijnum, "Failure Detection and
Locator Pair Exploration Protocol for IPv6 Multihoming",
RFC 5534, June 2009.
Appendix A. Other Solutions
Other than policy table distribution based approach, Aleksi Suhonen
proposed his idea [I-D.axu-addr-sel], where a host has a separate
routing table for each attached address. The document is still
incompleted, but basically it should have characteristics in common
with above mentioned policy table based mechanism except for the
implementation characteristics.
shim6 [RFC5533] was designed for site-multihoming. This mechanism
introduces a new sub-layer in IP layer, and new address selection
method for session initiation and session survivability. it is
documented in RFC 5534. [RFC5534] shim6 should fall into try-and-
error based category, in that it establishes a connection by trying
pairs of addresses.
Appendix B. Revision History
03:
Combined shim6 and try-and-error mechanisms into one section 3.3.
Removed deployment analysis in Section 4.
Made the introduction short and brief.
Added a reference to Design Team's work.
Added a reference to address selection conflict draft.
Created Appendix A. to mention about other solution proposals.
Conclusion and abstract was modified to reflect the discussion at
6man ML.
02:
Updated references for documents that were approved as RFCs.
Added reference to Hirotaka Matsuoka's try-and-error mechanism.
Added description about Aleksi Suhonen's routing table based
mechanism.
01:
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Corresponding to the increase of RFC 5221 requirements,
considerations about requirement #9, #10, #11 are added for each
approach.
00:
Approved as a 6man working group item.
Authors' Addresses
Arifumi Matsumoto
NTT PF Lab
Midori-Cho 3-9-11
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 3334
Email: arifumi@nttv6.net
Tomohiro Fujisaki
NTT PF Lab
Midori-Cho 3-9-11
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 7351
Email: fujisaki@syce.net
Ruri Hiromi
Intec Netcore, Inc.
Shinsuna 1-3-3
Koto-ku, Tokyo 136-0075
Japan
Phone: +81 3 5665 5069
Email: hiromi@inetcore.com
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