One document matched: draft-arifumi-6man-rfc3484-revise-00.txt
Network Working Group A. Matsumoto
Internet-Draft T. Fujisaki
Intended status: Standards Track NTT
Expires: December 21, 2008 R. Hiromi
Intec Netcore
K. Kanayama
INTEC Systems
June 19, 2008
Things To Be Considered for RFC 3484 Revision
draft-arifumi-6man-rfc3484-revise-00.txt
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Abstract
RFC 3484 has several known issues to be fixed mainly because of the
deprecation of IPv6 site-local unicast address and the coming of ULA.
Additionally, the rule 9 of the destination address selection rules,
namely the longest matching rule, is known for its adverse effect on
the round robin DNS technique. This document covers these essential
points to be modified and proposes possible useful changes to be
included in the revision of RFC 3484.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Problem Example . . . . . . . . . . . . . . . . . . . . . 3
2. Proposed Changes to RFC 3484 . . . . . . . . . . . . . . . . . 4
2.1. To remove site-local unicast address . . . . . . . . . . . 4
2.2. To change default policy table . . . . . . . . . . . . . . 5
2.3. To add ULA related considerations . . . . . . . . . . . . 6
2.4. To make address type dependent control possible . . . . . 6
2.5. To disable or restrict RFC 3484 Section 6 Rule 9 . . . . . 7
3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
RFC 3484 [RFC3484] defines default address selection rules for IPv6
and IPv4. Because of the deprecation of IPv6 site-local unicast
address and the coming of ULA, [RFC4193] these rules in RFC 3484 are
known to cause communication failures depending on the network
environment.
Additionally, there was a discussion at v6ops and ietf mailing lists
that the rule 9 of the destination address selection has a serious
adverse effect on the round robin DNS technique. [RFC1794] RFC 3484
defines that the destination address selection rule 9 should be
applied to both IPv4 and IPv6, which spoils the DNS based load
balancing technique that is widely used in the IPv4 Internet today.
This document covers these essential points to be modified and
proposes possible useful changes to be included in the revision of
RFC 3484.
1.1. Problem Example
When an enterprise has IPv4 Internet connectivity but does not yet
have IPv6 Internet connectivity, and the enterprise wants to provide
site-local IPv6 connectivity, ULA is the best choice for site-local
IPv6 connectivity. Each employee host will have both an IPv4 global
or private address and a ULA. Here, when this host tries to connect
to Host-C that has registered both A and AAAA records in the DNS, the
host will choose AAAA as the destination address and ULA for the
source address. This will clearly result in a connection failure.
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+--------+
| Host-C | AAAA = 2001:db8::80
+-----+--+ A = 192.47.163.1
|
============
| Internet |
============
| no IPv6 connectivity
+----+----+
| Gateway |
+----+----+
|
| fd01:2:3::/48 (ULA)
| 192.0.2.0/24
++--------+
| Router |
+----+----+
| fd01:2:3:4::/64 (ULA)
| 192.0.2.240/28
------+---+----------
|
+-+----+ fd01:2:3:4::100 (ULA)
| Host | 192.0.2.245
+------+
[Fig. 1]
This problem can be solved by adding one entry to the default policy
table. The changed table looks like this. The changes for the
default policy table are discussed at Section 2.2.
Prefix Pref Label
::1/128 50 0
::/0 40 1
2002::/16 30 2
fc00::/7 35 5 (added for ULA)
::/96 20 3
::ffff:0:0/96 10 4
This problem was mentioned at ipv6 mailing lists by Pekka Savola.
2. Proposed Changes to RFC 3484
2.1. To remove site-local unicast address
RFC3484 contains a few "site-local unicast" and "fec::" description.
It's better to remove examples related to site-local unicast address,
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or change examples to use ULA. Possible points to be re-written are
below.
- 2nd paragraph in Section 3.1 describes scope comparison
mechanism.
- Section 10 contains examples for site-local address.
2.2. To change default policy table
The default rule today is:
Prefix Precedence Label
::1/128 50 0
::/0 40 1
2002::/16 30 2
::/96 20 3
::ffff:0:0/96 10 4
The changes that should be included into the default policy table are
those rules that are universally useful and do no harm in every
reasonable network envionment. The changes we should consider for
the default policy table are as follows. The policy table is defined
to be configurable. The changes that are useful not universally but
locally can be put into the policy table manually or by using the
auto-configuration mechanism proposed as a DHCP option
[I-D.fujisaki-dhc-addr-select-opt].
- IPv4-compatible IPv6 address is deprecated. [RFC4291] (However,
should we keep this entry for the sake of backward compatibility
?)
- Teredo [RFC4380] is defined and has 2001::/32. Teredo's
priority should be less or equal to 6to4, considering its
characteristic of tunnel mechanism. About Windows, this point is
already in the implementation.
- ULA should have less precedence than Global IPv6 unicast
address. As described in Section 1.1, ULA is a possible cause of
connection failure. Things will worsen as IPv6 deployment
proceeds and more FQDNs have both A and AAAA records.
When we apply these changes, the default policy table looks like
this.
Prefix Precedence Label
::1/128 50 0
::/0 40 1
2002::/16 30 2
fc00::/7 20 3 (For ULA)
::ffff:0:0/96 10 4
2001::/32 5 5 (For Teredo)
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Teredo has the worst precedence. This means that, for IPv4-IPv6
dual-stack host, Teredo address will be used only when the
destination host has an IPv6 address only.
ULA has its own label and higher precedence than IPv4 address. This
means ULA will be used when the destination host also uses ULA. If a
host has a ULA and a IPv4 address, the host will not use ULA when
connecting to a dual-stack host in the Internet.
2.3. To add ULA related considerations
For example, we have to pay attention to source address selection for
a multicast packet. By default, ULA will be chosen for a multicast
packet of any scope.
This issue cannot be solved by changing a RFC 3484 rule. This is
because, multicast and unicast have different sets of scope and it is
site-dependent which unicast address scope is appropriate for the
site's multicast scope. Therefore, this issue can be solved, for
example, by configuring the policy table.
2.4. To make address type dependent control possible
It is hard to define default preferences for these address types, RA-
based, DHCP-based, manual-based, and privacy extention address,
because the appropriate preference value depends on the usage of
these addresses, but not on address types themselves. It is the
policy table where you can control host's address selection behavior.
For example, You can set priority on RFC 3041 [RFC3041] address
(privacy extension) by putting a line in policy table specifying RFC
3041 address by 128-bit prefixlen and continuing to update policy
table according to RFC 3041 address re-generation. But, this is
surely troublesome for users and implementers.
One idea is to update RFC 3484 policy table definition so that it can
handle meta addresses like privacy, DHCPv6 generated, RA generated,
manually generated (and even Home Address ?)
To prefer privacy address by default, and to prefer RA-generated
address for site internal, the policy table will look like this.
Prefix Pref Label
2001:db8:1234::(PRIVACY)/128 30 2
::/0 10 2
2001:db8:1234::(RA):/128 30 1
2001:db8::/48 20 1
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2.5. To disable or restrict RFC 3484 Section 6 Rule 9
There was a discussion at v6ops and ietf@ietf.org mailing lists that
the rule 9 of the destination address selection has a serious adverse
effect on the round robin DNS technique. RFC 3484 defines that the
destination address selection rule 9 should be applied to both IPv4
and IPv6, which spoils the DNS based load balancing technique that is
widely used in the IPv4 Internet today.
When the destination address acquired from one FQDN are two or more,
the Rule 9 defines that the longest matching destination and source
address pair should be chosen. As in RFC 1794, the DNS based load
balancing technique is achived by not re-ordering the destination
addresses returned from the DNS server. The Rule 9 defines
deterministic rule for re-ordering at hosts, hence the technique of
RFC 1794 is not available anymore.
Possible changes to RFC 3484 are as follows:
1. To delete Rule 9 completely.
2. To apply Rule 9 only for IPv6 and not for IPv4. In IPv6,
hiearchical address assignment is general principle, hence the
longest matchin rule is beneficial in many cases. In IPv4, as
stated above, the DNS based load balancing technique is widely
used.
3. To apply Rule 9 for IPv6 conditionally and not for IPv4. When
the length of matching bits of the destination address and the
source address is longer than N, the rule 9 is applied.
Otherwise, the order of the destination addresses do not change.
The N should be configurable and it should be 32 by default.
This is simply because the two sites whose matching bit length is
longer than 32 are probably adjacent.
Now that IPv6 PI address is admitted in some RIRs, hierachical
address assignment is not maintained anymore. It seems that the
longest matching algorithm is not worth the adverse effect of
disalbing the DNS based load balance technique. Therefore, the
proposal 1 or 3 seems to be preferable.
3. Conclusion
This document lists up several issues that should be included in the
revision of RFC 3484, which are useful universally and do no harm in
reasonable network environments.
The address selection rules that are useful locally can be
implemented, for example, by configuring the policy table. The
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policy distribution mechanism [I-D.fujisaki-dhc-addr-select-opt] may
be useful to configure a lot of hosts at a time.
The destination address selection rule 9 will spoil the DNS based
load balancing technique that is widely deployed at least in IPv4.
To keep this functionality in IPv6, the rule 9 have to be deleted or
restricted.
4. Security Considerations
No security risk is found that degrades RFC 3484.
5. IANA Considerations
Address type number for the policy table may have to be assigned by
IANA.
6. References
6.1. Normative References
[RFC1794] Brisco, T., "DNS Support for Load Balancing", RFC 1794,
April 1995.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
6.2. Informative References
[I-D.fujisaki-dhc-addr-select-opt]
Fujisaki, T., Matsumoto, A., Niinobe, S., Hiromi, R., and
K. Kanayama, "Distributing Address Selection Policy using
DHCPv6", draft-fujisaki-dhc-addr-select-opt-06 (work in
progress), June 2008.
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[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
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
Ken-ichi Kanayama
INTEC Systems Institute, Inc.
Shimoshin-machi 5-33
Toyama-shi, Toyama 930-0804
Japan
Phone: +81 76 444 8088
Email: kanayama_kenichi@intec-si.co.jp
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