draft-ietf-6man-rfc3484-revise-02.txt   draft-ietf-6man-rfc3484-revise-03.txt 
Network Working Group A. Matsumoto Network Working Group A. Matsumoto
Internet-Draft J. Kato Internet-Draft J. Kato
Intended status: Standards Track T. Fujisaki Intended status: Standards Track T. Fujisaki
Expires: September 15, 2011 NTT Expires: December 12, 2011 NTT
March 14, 2011 June 10, 2011
Update to RFC 3484 Default Address Selection for IPv6 Update to RFC 3484 Default Address Selection for IPv6
draft-ietf-6man-rfc3484-revise-02.txt draft-ietf-6man-rfc3484-revise-03.txt
Abstract Abstract
RFC 3484 describes algorithms for source address selection and for RFC 3484 describes algorithms for source address selection and for
destination address selection. The algorithms specify default destination address selection. The algorithms specify default
behavior for all Internet Protocol version 6 (IPv6) implementations. behavior for all Internet Protocol version 6 (IPv6) implementations.
This document specifies a set of updates that modify the algorithms This document specifies a set of updates that modify the algorithms
and provide fixes for the identified issues. and fix the known defects.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 15, 2011. This Internet-Draft will expire on December 12, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 23 skipping to change at page 2, line 23
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Changes related to the default policy table . . . . . . . 3 2.1. Changes related to the default policy table . . . . . . . 3
2.1.1. ULAs in the policy table . . . . . . . . . . . . . . . 4 2.1.1. ULA in the policy table . . . . . . . . . . . . . . . 4
2.1.2. Teredo in the policy table . . . . . . . . . . . . . . 4 2.1.2. Teredo in the policy table . . . . . . . . . . . . . . 4
2.1.3. Deprecated addresses in the policy table . . . . . . . 4 2.1.3. 6to4, Teredo, and IPv4 prioritization . . . . . . . . 4
2.1.4. Renewed default policy table . . . . . . . . . . . . . 4 2.1.4. Deprecated addresses in the policy table . . . . . . . 5
2.1.5. Renewed default policy table . . . . . . . . . . . . . 5
2.2. The longest matching rule . . . . . . . . . . . . . . . . 5 2.2. The longest matching rule . . . . . . . . . . . . . . . . 5
2.3. Utilize next-hop for source address selection . . . . . . 5 2.3. Utilize next-hop for source address selection . . . . . . 6
2.4. Private IPv4 address scope . . . . . . . . . . . . . . . . 6 2.4. Private IPv4 address scope . . . . . . . . . . . . . . . . 6
2.5. Deprecation of site-local unicast address . . . . . . . . 6 2.5. Deprecation of site-local unicast address . . . . . . . . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . 7 3. Security Considerations . . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . . 7 5.1. Normative References . . . . . . . . . . . . . . . . . . . 7
5.2. Informative References . . . . . . . . . . . . . . . . . . 8 5.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Appendix B. Discussion . . . . . . . . . . . . . . . . . . . . . 8 Appendix B. Past Discussion . . . . . . . . . . . . . . . . . . . 9
B.1. Centrally assigned ULA . . . . . . . . . . . . . . . . . . 8 B.1. The longest match rule . . . . . . . . . . . . . . . . . . 9
B.2. 6to4, Teredo, and IPv4 prioritization . . . . . . . . . . 9 B.2. NAT64 prefix issue . . . . . . . . . . . . . . . . . . . . 10
B.3. Deprecated address . . . . . . . . . . . . . . . . . . . . 9
B.4. The longest match rule . . . . . . . . . . . . . . . . . . 9
Appendix C. Revision History . . . . . . . . . . . . . . . . . . 10 Appendix C. Revision History . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
The IPv6 addressing architecture [RFC4291] allows multiple unicast The IPv6 addressing architecture [RFC4291] allows multiple unicast
addresses to be assigned to interfaces. Because of this IPv6 addresses to be assigned to interfaces. Because of this IPv6
implementations need to handle multiple possible source and implementations need to handle multiple possible source and
destination addresses when initiating communication. RFC 3484 destination addresses when initiating communication RFC 3484
[RFC3484] specifies the default algorithms, common across all [RFC3484]. specifies the default algorithms, common across all
implementations, for selecting source and destination addresses so implementations, for selecting source and destination addresses so
that it is easier to predict the address selection behavior. that it is easier to predict the address selection behavior.
Since RFC 3484 was published, some issues have been identified with After RFC 3484 was specified, some issues have been identified with
the algorithm specified there. The issues are related to the longest the algorithm specified there. The issues are related to the longest
match algorithm used in Rule 9 of Destination address selection match algorithm used in Rule 9 of Destination address selection
breaking DNS round-robin techniques, and prioritization of poor IPv6 breaking DNS round-robin techniques, and prioritization of poor IPv6
connectivity using transition mechanisms over native IPv4 connectivity using transition mechanisms over native IPv4
connectivity. connectivity.
There have also been some significant changes to the IPv6 addressing There have also been some significant changes to the IPv6 addressing
architecture that require changes in the RFC 3484 policy table. Such architecture that require changes in the RFC 3484 policy table. Such
changes include the deprecation of site-local unicast addresses changes include the deprecation of site-local unicast addresses
[RFC3879] and the IPv4-compatible IPv6 addresses, the introduction of [RFC3879] and the IPv4-compatible IPv6 addresses, the introduction of
Unique Local Addresses [RFC4193] etc. Unique Local Addresses [RFC4193] etc.
This document specifies a set of updates that modify the algorithms This document specifies a set of updates that modify the algorithms
and provide fixes for the identified issues. and fix the known defects.
2. Specification 2. Specification
2.1. Changes related to the default policy table 2.1. Changes related to the default policy table
The default policy table is defined in RFC 3484 Section 2.1 as The default policy table is defined in RFC 3484 Section 2.1 as
follows: follows:
Prefix Precedence Label Prefix Precedence Label
::1/128 50 0 ::1/128 50 0
::/0 40 1 ::/0 40 1
2002::/16 30 2 2002::/16 30 2
::/96 20 3 ::/96 20 3
::ffff:0:0/96 10 4 ::ffff:0:0/96 10 4
The changes that should be included into the default policy table are The changes that should be included into the default policy table are
those rules that are universally useful and do no harm in every those rules that are universally useful and do no harm in every
reasonable network environment. The changes we should consider for reasonable network envionment. The changes we should consider for
the default policy table are listed in this sub-section. the default policy table are listed in this sub-section.
The policy table is defined to be configurable. If the local site The policy table is defined to be configurable. The changes that are
policy needs to be different changes can be put into the policy table useful not universally but locally can be put into the policy table
manually or by using the auto-configuration mechanism proposed as a manually or by using the auto-configuration mechanism proposed as a
DHCP option [I-D.ietf-6man-addr-select-opt]. DHCP option [I-D.ietf-6man-addr-select-opt].
2.1.1. ULAs in the policy table 2.1.1. ULA in the policy table
RFC 5220 [RFC5220] Section 2.1.4, 2.2.2, and 2.2.3 describes address RFC 5220 [RFC5220] Section 2.1.4, 2.2.2, and 2.2.3 describes address
selection problems related to ULAs [RFC4193]. These problems can be selection problems related to ULA [RFC4193]. These problems can be
solved by either changing the scope of ULAs to site-local, or by solved by either changing the scope of ULA to site-local, or by
adding an entry to the default policy table entry that has its own adding an entry for default policy table entry that has its own label
label for ULAs. for ULA.
ULAs has been specified with a global scope because the reachability Centrally assigned ULA [I-D.ietf-ipv6-ula-central] is proposed, and
of the ULAs was intended to be restricted by the routing system. is assigned fc00::/8. Using the different labels for fc00::/8 and
Since a ULA will not be exposed outside of its reachability domain, fd00::/8 makes sense if we assume the same kind of address block is
if a ULA is available as a candidate destination address, it can be assigned in the same or adjacent network. However, we cannot expect
expected to be reachable. In fact, such ULA to ULA communication is that the type of ULA address block and network adjancency commonly
often desired (in particular in sites where ULAs are intended to have any relationships.
provide stable addresses when the global prefix may be changing) and
thus needs to be prioritized.
Therefore, the scope of ULA should be kept global, and prioritization Regarding the scope of ULA, ULA has been specified with a global
of ULA to ULA communication should be implemented in the policy scope because the reachability of the ULA was intended to be
table, by assigning a specific label for ULAs using fc00::/7. restricted by the routing system. Since the ULAs will not be exposed
outside of its reachability domain, if an ULA is available as a
candidate destination address, it can be expected to be reachable.
if we change the scope of ULA smaller than global, we can prioritize
ULA to ULA communication over GUA to GUA communication. At the same
time, however, finer-grained configuration of ULA address selection
will be impossible. For example, even if you want to priorize
communication related to the only /48 ULA prefix used in your site,
and do not want to prioritize communication to any other ULA prefix,
such a policy cannot be implemented in the policy table. So, this
draft proposes the use of the policy table to differentiate ULA from
GUA.
2.1.2. Teredo in the policy table 2.1.2. Teredo in the policy table
Teredo [RFC4380] is defined and has been assigned 2001::/32. This Teredo [RFC4380] is defined and has been assigned 2001::/32. This
address block should be assigned its own label in the policy table. address block should be assigned its own label in the policy table.
Teredo's priority should be less than or equal to 6to4, considering Teredo's priority should be less or equal to 6to4, considering its
its characteristic of being a transitional tunnel mechanism. Windows characteristic of transitional tunnel mechanism. About Windows, this
already implements this. is already in the implementation.
2.1.3. Deprecated addresses in the policy table 2.1.3. 6to4, Teredo, and IPv4 prioritization
IPv4-compatible IPv6 addresses are deprecated [RFC4291]. IPv6 site- Regarding the prioritization between IPv4 and these transitional
local unicast addresses are deprecated [RFC3879]. Moreover, the mechanisms, the connectivity of them are known to be worse than IPv4.
6bone testing address has also been phased out[RFC3701]. The issue These mechiansms are said to be the last resort access to IPv6
is how we treat these outdated addresses. resources. While 6to4 should have higher precedence over Teredo, in
that 6to4 host to 6to4 host communication can be over IPv4, which can
result in more optimal path, and 6to4 does not need NAT traversal.
2.1.4. Renewed default policy table 2.1.4. Deprecated addresses in the policy table
After applying these updates, the default policy table becomes: IPv4-compatible IPv6 address (::/96) is deprecated [RFC4291]. IPv6
site-local unicast address (fec0::/10) is deprecated [RFC3879]. 6bone
testing address [RFC3701] was returned.
These addresses were removed from the current specification. So, it
should not be treated differently, especially if we plan future re-
use of these address blocks. Hense, 6bone testing address block
should not be treated specially.
Considering the inappropriate use of these address blocks especially
in outdated implementations and bad effects brought by them, it
should be labeled differently from the legitimate address blocks as
far as the address block is reserved by IANA.
2.1.5. Renewed default policy table
After applying these updates, the default policy table will be:
Prefix Precedence Label Prefix Precedence Label
::1/128 60 0 ::1/128 60 0
fc00::/7 50 1 fc00::/7 50 1
::/0 40 2 ::/0 40 2
::ffff:0:0/96 30 3 ::ffff:0:0/96 30 3
2002::/16 20 4 2002::/16 20 4
2001::/32 10 5 2001::/32 10 5
::/96 1 10 ::/96 1 10
fec::/16 1 11 fec0::/10 1 11
3ffe::/16 1 12
2.2. The longest matching rule 2.2. The longest matching rule
This issue is related to a problem with the longest matching rule, as This issue is related to the longest matching rule, which was found
reported by Dave Thaler. It is a malfunction of the DNS round-robin by Dave Thaler. It is malfunction of DNS round robin technique. It
technique. It is common for both IPv4 and IPv6. is common for both IPv4 and IPv6.
When a destination address DA, DB, and the source address of DA When a destination address DA, DB, and the source address of DA
Source(DA) are on the same subnet and Source(DA) == Source(DB), DNS Source(DA) are on the same subnet and Source(DA) == Source(DB), DNS
round robin load-balancing cannot function. By considering prefix round robin load-balancing cannot function. By considering prefix
lengths that are longer than the subnet prefix, this rule establishes lengths that are longer than the subnet prefix, this rule establishes
preference between addresses that have no substantive differences preference between addresses that have no substantive differences
between them. The rule functions as an arbitrary tie-breaker between between them. The rule functions as an arbitrary tie-breaker between
the hosts in a round robin, causing a given host to always prefer a the hosts in a round robin, causing a given host to always prefer a
given member of the round robin. given member of the round robin.
skipping to change at page 5, line 48 skipping to change at page 6, line 22
When DA and DB belong to the same address family (both are IPv6 or When DA and DB belong to the same address family (both are IPv6 or
both are IPv4): If CommonPrefixLen(DA & Netmask(Source(DA)), both are IPv4): If CommonPrefixLen(DA & Netmask(Source(DA)),
Source(DA)) > CommonPrefixLen(DB & Netmask(Source(DB)), Source(DB)), Source(DA)) > CommonPrefixLen(DB & Netmask(Source(DB)), Source(DB)),
then prefer DA. Similarly, if CommonPrefixLen(DA & then prefer DA. Similarly, if CommonPrefixLen(DA &
Netmask(Source(DA)), Source(DA)) < CommonPrefixLen(DB & Netmask(Source(DA)), Source(DA)) < CommonPrefixLen(DB &
Netmask(Source(DB)), Source(DB)), then prefer DB. Netmask(Source(DB)), Source(DB)), then prefer DB.
2.3. Utilize next-hop for source address selection 2.3. Utilize next-hop for source address selection
RFC 3484 source address selection rule 5 states that the address that The RFC 3484 source address selection rule 5 defines the address that
is attached to the outgoing interface should be preferred as the is attached to the outgoing interface should be preferred as the
source address. This rule is reasonable considering the prevalence source address. This rule is reasonable considering the prevalence
of Ingress Filtering described in BCP 38 [RFC2827]. This is because of Ingress Filtering described in BCP 38 [RFC2827]. This is because
an upstream network provider usually assumes it receives those an upstream network provider usually assumes it receives those
packets from customers that will use the delegated addresses as their packets from their customer that have the delegated addresses as the
source addresses. source addresses.
This rule, however, is not effective in an environment such as This rule, however, is not effective in such a environment described
described in RFC 5220 Section 2.1.1, where a host has multiple in RFC 5220 Section 2.1.1, where a host has multiple upstream routers
upstream routers on the same link and has addresses delegated from on the same link and has addresses delegated from each upstream
each upstream on single interface. routers on single interface.
So, a new rule 5.1 that utilizes next-hop information for source So, a new rule 5.1 that utilizes next-hop information for source
address selection is inserted just after the rule 5. address selection is inserted just after the rule 5.
Rule 5.1: Use an address assigned by the selected next-hop. Rule 5.1: Use an address assigned by the selected next-hop.
If SA is assigned by the selected next-hop that will be used to send If SA is assigned by the selected next-hop that will be used to send
to D and SB is assigned by a different next-hop, then prefer SA. to D and SB is assigned by a different next-hop, then prefer SA.
Similarly, if SB is assigned by the next-hop that will be used to Similarly, if SB is assigned by the next-hop that will be used to
send to D and SA is assigned by a different next-hop, then prefer SB. send to D and SA is assigned by a different next-hop, then prefer SB.
skipping to change at page 6, line 40 skipping to change at page 7, line 15
The algorithm currently specified in RFC 3484 is based on the The algorithm currently specified in RFC 3484 is based on the
assumption that a source address with a small scope cannot reach a assumption that a source address with a small scope cannot reach a
destination address with a larger scope. This assumption does not destination address with a larger scope. This assumption does not
hold if private IPv4 addresses and a NAT are used to reach public hold if private IPv4 addresses and a NAT are used to reach public
IPv4 addresses. IPv4 addresses.
Due to this assumption, in the presence of both NATed private IPv4 Due to this assumption, in the presence of both NATed private IPv4
address and transitional addresses (like 6to4 and Teredo), the host address and transitional addresses (like 6to4 and Teredo), the host
will choose the transitional IPv6 address to access dual-stack peers will choose the transitional IPv6 address to access dual-stack peers
[I-D.denis-v6ops-nat-addrsel]. Choosing transitional IPv6 [I-D.denis-v6ops-nat-addrsel]. Choosing transitional IPv6
connectivity over native IPv4 connectivity is not desirable. connectivity over native IPv4 connectivity is not considered to be a
very wise result.
This issue can be fixed by changing the address scope of private IPv4 This issue can be fixed by changing the address scope of private IPv4
addresses to global. Such a change has already been implemented in addresses to global. Such change has already been implemented in
some OSes. some OSes.
2.5. Deprecation of site-local unicast address 2.5. Deprecation of site-local unicast address
RFC 3484 contains a few "site-local unicast" and "fec::" RFC 3484 contains a few "site-local unicast" and "fec0::"
descriptions. It's better to remove examples related to site-local description. It's better to remove examples related to site-local
unicast address, or change examples to use ULAs. Points that need to unicast address, or change examples to use ULA. Possible points to
be re-written are: be re-written are below.
- the 2nd paragraph in RFC 3484 Section 3.1 describing the scope - 2nd paragraph in RFC 3484 Section 3.1 describes scope comparison
comparison mechanism. mechanism.
- RFC 3484 Section 10 containing examples for site-local address. - RFC 3484 Section 10 contains examples for site-local address.
3. Security Considerations 3. Security Considerations
No security risk is found that degrades RFC 3484. No security risk is found that degrades RFC 3484.
4. IANA Considerations 4. IANA Considerations
An address type number for the policy table may have to be assigned Address type number for the policy table may have to be assigned by
by IANA. IANA.
5. References 5. References
5.1. Normative References 5.1. Normative References
[RFC1794] Brisco, T., "DNS Support for Load Balancing", RFC 1794, [RFC1794] Brisco, T., "DNS Support for Load Balancing", RFC 1794,
April 1995. April 1995.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", E. Lear, "Address Allocation for Private Internets",
skipping to change at page 8, line 9 skipping to change at page 8, line 33
Network Address Translations (NATs)", RFC 4380, Network Address Translations (NATs)", RFC 4380,
February 2006. February 2006.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, [RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in Multi- "Problem Statement for Default Address Selection in Multi-
Prefix Environments: Operational Issues of RFC 3484 Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008. Default Rules", RFC 5220, July 2008.
5.2. Informative References 5.2. Informative References
[I-D.chown-addr-select-considerations]
Chown, T., "Considerations for IPv6 Address Selection
Policy Changes", draft-chown-addr-select-considerations-03
(work in progress), July 2009.
[I-D.denis-v6ops-nat-addrsel] [I-D.denis-v6ops-nat-addrsel]
Denis-Courmont, R., "Problems with IPv6 source address Denis-Courmont, R., "Problems with IPv6 source address
selection and IPv4 NATs", draft-denis-v6ops-nat-addrsel-00 selection and IPv4 NATs", draft-denis-v6ops-nat-addrsel-00
(work in progress), February 2009. (work in progress), February 2009.
[I-D.ietf-6man-addr-select-considerations]
Chown, T., "Considerations for IPv6 Address Selection
Policy Changes",
draft-ietf-6man-addr-select-considerations-02 (work in
progress), July 2010.
[I-D.ietf-6man-addr-select-opt] [I-D.ietf-6man-addr-select-opt]
Matsumoto, A., Fujisaki, T., and J. Kato, "Distributing Matsumoto, A., Fujisaki, T., and J. Kato, "Distributing
Address Selection Policy using DHCPv6", Address Selection Policy using DHCPv6",
draft-ietf-6man-addr-select-opt-00 (work in progress), draft-ietf-6man-addr-select-opt-00 (work in progress),
December 2010. December 2010.
[I-D.ietf-ipv6-ula-central] [I-D.ietf-ipv6-ula-central]
Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-ula-central-02 (work in Addresses", draft-ietf-ipv6-ula-central-02 (work in
progress), June 2007. progress), June 2007.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000. Address Spoofing", BCP 38, RFC 2827, May 2000.
Appendix A. Acknowledgements [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
The authors would like to thank to Dave Thaler, Pekka Savola, Remi October 2010.
Denis-Courmont and the members of 6man's address selection design
team for their invaluable contributions to this document.
Appendix B. Discussion
B.1. Centrally assigned ULA
Discussion: Centrally assigned ULA [I-D.ietf-ipv6-ula-central] is
proposed, and assigned fc00::/8. Using the different labels for
fc00::/8 and fd00::/8 makes sense if we can assume the same kind
of address block is assigned in the same or adjacent network.
However, the way of assignment and network adjancency may not have
any relationships.
B.2. 6to4, Teredo, and IPv4 prioritization
Discussion: Regarding the prioritization between IPv4 and these Appendix A. Acknowledgements
transitional mechanisms, their connectivity quality is recently
known to be worse than IPv4. These mechiansms are said to be the
last resort access to IPv6 resources. The 6to4 should have higher
precedence over Teredo, in that 6to4 host to 6to4 host
communication runs over IPv4, which can result in a more optimal
path, and 6to4 does not need NAT traversal.
B.3. Deprecated address Authors would like to thank to Dave Thaler, Pekka Savola, Remi Denis-
Courmont and the members of 6man's address selection design team for
their invaluable contributions to this document.
Discussion: These addresses were removed from the current Appendix B. Past Discussion
specification. So, they should not be treated differently,
especially if we think about future re-use of these address
blocks.
Considering the inappropriate use of these address blocks, This section summarizes discussions we had before related to address
especially in outdated implementations, and bad effects caused by selection mechanisms.
them, however, they should be labeled differently from the
legitimate address blocks.
Or should we keep this entry for the sake of backward
compatibility?
B.4. The longest match rule B.1. The longest match rule
RFC 3484 defines that the destination address selection rule 9 should RFC 3484 defines that the destination address selection rule 9 should
be applied to both IPv4 and IPv6, which spoils the DNS based load be applied to both IPv4 and IPv6, which spoils the DNS based load
balancing technique that is widely used in the IPv4 Internet today. balancing technique that is widely used in the IPv4 Internet today.
When two or more destination addresses are acquired from one FQDN, When two or more destination addresses are acquired from one FQDN,
rule 9 states that the longest matching destination and source the rule 9 defines that the longest matching destination and source
address pair should be chosen. As stated in RFC 1794, the DNS based address pair should be chosen. As in RFC 1794, the DNS based load
load balancing technique is achieved by not re-ordering the balancing technique is achived by not re-ordering the destination
destination addresses returned from the DNS server. Rule 9 defines a addresses returned from the DNS server. The Rule 9 defines
deterministic rule for re-ordering at hosts, hence the technique of deterministic rule for re-ordering at hosts, hence the technique of
RFC 1794 is not available anymore. RFC 1794 is not available anymore.
Regarding this problem, there was discussion in the IETF and other Regarding this problem, there was discussion in IETF and other places
places that led to some different options being suggested, as listed like below.
below.
Discussion: The possible changes to RFC 3484 are as follows: Discussion: The possible changes to RFC 3484 are as follows:
1. To delete Rule 9 completely. 1. To delete Rule 9 completely.
2. To apply Rule 9 only for IPv6 and not for IPv4. In IPv6, 2. To apply Rule 9 only for IPv6 and not for IPv4. In IPv6,
hierarchical address assignment is a general principle, hence the hiearchical address assignment is general principle, hence the
longest matching rule is beneficial in many cases. In IPv4, as longest matchin rule is beneficial in many cases. In IPv4, as
stated above, the DNS based load balancing technique is widely stated above, the DNS based load balancing technique is widely
used. used.
3. To apply Rule 9 for IPv6 conditionally and not for IPv4. When 3. To apply Rule 9 for IPv6 conditionally and not for IPv4. When
the length of matching bits of the destination address and the the length of matching bits of the destination address and the
source address is longer than N, rule 9 is applied. Otherwise, source address is longer than N, the rule 9 is applied.
the order of the destination addresses do not change. The N Otherwise, the order of the destination addresses do not change.
should be configurable and it should be 32 by default. This is The N should be configurable and it should be 32 by default.
simply because the two sites whose matching bit length is longer This is simply because the two sites whose matching bit length is
than 32 are probably adjacent. longer than 32 are probably adjacent.
Now that IPv6 PI addressing is being assigned by some RIRs, Now that IPv6 PI address is admitted in some RIRs, hierachical
hierachical address assignment is not fully maintained anymore. It address assignment is not maintained anymore. It seems that the
seems that the longest matching algorithm may not be worth the longest matching algorithm may not worth the adverse effect of
adverse effect of disalbing the DNS based load balance technique. disalbing the DNS based load balance technique.
After long discussion, however we could not reach any consensus here.
That means, we cannot change the current rules for this issue.
B.2. NAT64 prefix issue
NAT64 WKP was newly defined[RFC6052]. It depends site by site
whether NAT64 should be preferred over IPv4, in other words NAT44, or
NAT44 over NAT64. So, this issue of site local policy should be
solved by policy distribution mechanism.
Appendix C. Revision History Appendix C. Revision History
03:
ULA address selection issue was expanded.
6to4, Teredo and IPv4 priorization issue was elaborated.
Deperecated address blocks in policy table section was elaborated.
In appendix, NAT64 prefix issue was added.
02: 02:
Suresh Krishnan's comments were incorporated. Suresh Krishnan's suggestions for better english sentences were
incorporated.
A new source address selection rule that utilizes the next-hop A new source address selection rule that utilizes the next-hop
information is included in Section 2.3 information is included in Section 2.3.
Site local address prefix was corrected.
01: 01:
Restructured to contain only the actual changes to RFC 3484. Re-structured to contain only the actual changes to RFC 3484.
00: 00:
Published as a 6man working group item. Published as a 6man working group item.
03: 03:
Added acknowledgements. Added acknowledgements.
Added longest matching algorithm malfunction regarding local DNS Added longest matching algorithm malfunction regarding local DNS
round robin. round robin.
The proposed changes section was restructured. The proposed changes section was re-structured.
The issue of 6to4/Teredo and IPv4 prioritization was included. The issue of 6to4/Teredo and IPv4 prioritization was included.
The issue of deprecated addresses was added. The issue of deprecated addresses was added.
The renewed default policy table was changed accordingly. The renewed default policy table was changed accordingly.
02: 02:
Added the reference to address selection design team's proposal. Added the reference to address selection design team's proposal.
01: 01:
The issue of private IPv4 address scope was added. The issue of private IPv4 address scope was added.
The issue of ULA address scope was added. The issue of ULA address scope was added.
Discussion of longest matching rule was expanded. Discussion of longest matching rule was expanded.
Authors' Addresses Authors' Addresses
Arifumi Matsumoto Arifumi Matsumoto
NTT SI Lab NTT SI Lab
Midori-Cho 3-9-11 Midori-Cho 3-9-11
Musashino-shi, Tokyo 180-8585 Musashino-shi, Tokyo 180-8585
 End of changes. 54 change blocks. 
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