--- 1/draft-ietf-6man-rfc3484-revise-00.txt 2010-10-15 09:14:56.000000000 +0200 +++ 2/draft-ietf-6man-rfc3484-revise-01.txt 2010-10-15 09:14:56.000000000 +0200 @@ -1,47 +1,44 @@ Network Working Group A. Matsumoto Internet-Draft J. Kato Intended status: Standards Track T. Fujisaki -Expires: March 17, 2011 NTT - September 13, 2010 +Expires: April 18, 2011 NTT + October 15, 2010 - Things To Be Included in RFC 3484 Revision - draft-ietf-6man-rfc3484-revise-00.txt + Update to RFC 3484 Default Address Selection for IPv6 + draft-ietf-6man-rfc3484-revise-01.txt Abstract - RFC 3484 has several known issues to be fixed. Deprecation of IPv6 - site-local unicast address and the coming of ULA brought some - preferable changes to the rules. 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 points to be fixed and - proposes possible useful changes to be included in the revision of - RFC 3484. + RFC 3484 describes algorithms for source address selection and for + destination address selection. The algorithms specify default + behavior for all Internet Protocol version 6 (IPv6) implementations. + This document specifies a set of updates that modify the algorithms + and fix the known defects. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on March 17, 2011. + This Internet-Draft will expire on April 18, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -58,116 +55,61 @@ modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 1.1. Problem Example . . . . . . . . . . . . . . . . . . . . . 4 - 2. Proposed Changes to RFC 3484 . . . . . . . . . . . . . . . . . 5 - 2.1. Changes related to the default policy table . . . . . . . 5 - 2.1.1. Arrival of ULA . . . . . . . . . . . . . . . . . . . . 6 - 2.1.2. Arrival of Teredo and harm of transitional - mechanisms . . . . . . . . . . . . . . . . . . . . . . 6 - 2.1.3. Deprecated addresses . . . . . . . . . . . . . . . . . 7 - 2.1.4. Renewed default policy table . . . . . . . . . . . . . 7 - 2.2. Source address selection for multicast packet . . . . . . 7 - 2.3. RFC 3484 Section 6 Rule 9 and DNS round robin . . . . . . 8 - 2.4. RFC 3484 Section 6 Rule 9 and local DNS round robin . . . 9 - 2.5. Deprecation of site-local unicast address . . . . . . . . 9 - 2.6. Private IPv4 address scope . . . . . . . . . . . . . . . . 10 - 3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 4. Security Considerations . . . . . . . . . . . . . . . . . . . 10 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 - 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 6.1. Normative References . . . . . . . . . . . . . . . . . . . 11 - 6.2. Informative References . . . . . . . . . . . . . . . . . . 12 - Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12 - Appendix B. Revision History . . . . . . . . . . . . . . . . . . 12 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Specification . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2.1. Changes related to the default policy table . . . . . . . . 3 + 2.1.1. ULA in the policy table . . . . . . . . . . . . . . . . 3 + 2.1.2. Teredo in the policy table . . . . . . . . . . . . . . 4 + 2.1.3. Deprecated addresses in the policy table . . . . . . . 4 + 2.1.4. Renewed default policy table . . . . . . . . . . . . . 4 + 2.2. The longest matching rule . . . . . . . . . . . . . . . . . 5 + 2.3. Private IPv4 address scope . . . . . . . . . . . . . . . . 5 + 2.4. Deprecation of site-local unicast address . . . . . . . . . 6 + 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 + 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 + 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 5.1. Normative References . . . . . . . . . . . . . . . . . . . 6 + 5.2. Informative References . . . . . . . . . . . . . . . . . . 7 + Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 7 + Appendix B. Discussion . . . . . . . . . . . . . . . . . . . . . . 7 + B.1. Centrally assigned ULA . . . . . . . . . . . . . . . . . . 7 + B.2. 6to4, Teredo, and IPv4 prioritization . . . . . . . . . . . 8 + B.3. Deprecated address . . . . . . . . . . . . . . . . . . . . 8 + B.4. The longest match rule . . . . . . . . . . . . . . . . . . 8 + Appendix C. Revision History . . . . . . . . . . . . . . . . . . . 9 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction - RFC 3484 [RFC3484] defines default address selection rules for IPv6 - and IPv4. Because of the deprecation of IPv6 site-local unicast - address[RFC3879] 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. - - Remi Denis-Courmont summarized NAT related address selection problems - and possible solutions in [I-D.denis-v6ops-nat-addrsel]. - - Problems related to IPv6 and IPv4 address selection are described in - RFC 5220 [RFC5220]. Some of them can be fixed by updating RFC 3484, - and some of the others are solved by address selection design team's - proposal [I-D.chown-addr-select-considerations]. - - This document covers these points to be fixed 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 [RFC1918] 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. - - +--------+ - | 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] + RFC 3484 describes algorithms for source address selection and for + destination address selection. The algorithms specify default + behavior for all Internet Protocol version 6 (IPv6) implementations. - This problem can be solved by changing the scope of ULA to site- - local, or by adding one entry to the default policy table that sets - lower priority for ULA than IPv4 address. + RFC 3484 has several known issues to be fixed. Deprecation of IPv6 + site-local unicast address and the coming of ULA brought some + preferable changes to the rules. 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 problem was mentioned at ipv6 mailing lists by Pekka Savola. + This document specifies a set of updates that modify the algorithms + and fix the known defects. -2. Proposed Changes to RFC 3484 +2. Specification 2.1. Changes related to the default policy table The default policy table is defined in RFC 3484 Section 2.1 as follows: Prefix Precedence Label ::1/128 50 0 ::/0 40 1 2002::/16 30 2 @@ -177,163 +119,77 @@ 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 listed in this sub-section. 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]. -2.1.1. Arrival of ULA +2.1.1. ULA in the policy table RFC 5220 Section 2.1.4, 2.2.2, and 2.2.3 describes address selection problems related to ULA. These problems can be solved by changing - the scope of ULA to site-local, or by adding an entry for default + the scope of ULA to site-local, and/or by adding an entry for default policy table entry that has its own label for ULA. In its nature, ULA has global scope. This is because ULA's scope is - defined to be defined in routing mechanism. It may be the case that + expected to be defined in routing system. It may be the case that ULA and global IPv6 address are used for source and destination addresses of communication. On the other hand, to prioritize ULA to ULA communication is basically reasonable. ULA should not be exposed to outside of its routable routing domain, so if ULA is given from the application as a candidate destination address, it can be generally expected that the ULA is within or at least close to the source host. - Therefore, the scope of ULA should be global, and prioritization of - ULA to ULA communication should be implemented in policy table, by + Therefore, the scope of ULA should be kept global, and prioritization + of ULA to ULA communication should be implemented in policy table, by assigning its own label for ULA fc00::/7. - 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. - -2.1.2. Arrival of Teredo and harm of transitional mechanisms +2.1.2. Teredo in the policy table - Teredo [RFC4380] is defined and has been assigned 2001::/32. + Teredo [RFC4380] is defined and has been assigned 2001::/32. This + address block should be assigned its own label in the policy table. Teredo's priority should be less or equal to 6to4, considering its - characteristic of tunnel mechanism. About Windows, this is already - in the implementation. - - Discussion: Regarding the prioritization between IPv4 and these - transitional mechanisms, the connectivity of them are recently - known to be worse than IPv4. These mechiansms are said to be the - last resort access to IPv6 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. + characteristic of transitional tunnel mechanism. About Windows, this + is already in the implementation. -2.1.3. Deprecated addresses +2.1.3. Deprecated addresses in the policy table IPv4-compatible IPv6 address is deprecated. [RFC4291] IPv6 site- local unicast address is deprecated. [RFC3879] Moreover, 6bone testing address was [RFC3701] The issue is how we treat these outdated addresses. - Discussion: These addresses was removed from the current - specification. So, it 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 - especially in outdated implementations and bad effects brought by - them, however, it should be labeled differently from the - legitimate address blocks. - 2.1.4. Renewed default policy table - When we apply these changes, the default policy table will be: + After applying these updates, the default policy table will be: Prefix Precedence Label ::1/128 60 0 fc00::/7 50 1 ::/0 40 2 ::ffff:0:0/96 30 3 2002::/16 20 4 2001::/32 10 5 ::/96 1 10 fec::/16 1 11 3ffe::/16 1 12 -2.2. Source address selection for multicast packet - - Source address selection for a multicast packet easily fails. It is - suggested to add some notes describing this issue of multicast - address selection. - - As described in RFC 5220 Section 2.1.6, 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 per-site. - -2.3. RFC 3484 Section 6 Rule 9 and DNS round robin - - 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. - - Regarding this problem, there was discussion in IETF and other places - like below. - http://drplokta.livejournal.com/109267.html - http://www.ietf.org/mail-archive/web/ietf/current/msg51874.html - http://www.ietf.org/mail-archive/web/discuss/current/msg01035.html - http://www.ietf.org/mail-archive/web/dnsop/current/msg05847.html - http://lists.debian.org/debian-ctte/2007/11/msg00029.html - http://www.ietf.org/mail-archive/web/ietf/current/msg55991.html - - Discussion: The 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 may not worth the adverse effect of - disalbing the DNS based load balance technique. - -2.4. RFC 3484 Section 6 Rule 9 and local DNS round robin +2.2. The longest matching rule - There is another issue related to the longest matching rule, which - was found by Dave Thaler. It is also malfunction of DNS round robin - technique. It is common for both IPv4 and IPv6. + This issue is related to the longest matching rule, which was found + by Dave Thaler. It is malfunction of DNS round robin technique. It + is common for both IPv4 and IPv6. 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 round robin load-balancing cannot function. By considering prefix lengths that are longer than the subnet prefix, this rule establishes preference between addresses that have no substantive differences 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 given member of the round robin. @@ -345,79 +201,61 @@ Rule 9: Use longest matching prefix. When DA and DB belong to the same address family (both are IPv6 or both are IPv4): If CommonPrefixLen(DA & Netmask(Source(DA)), Source(DA)) > CommonPrefixLen(DB & Netmask(Source(DB)), Source(DB)), then prefer DA. Similarly, if CommonPrefixLen(DA & Netmask(Source(DA)), Source(DA)) < CommonPrefixLen(DB & Netmask(Source(DB)), Source(DB)), then prefer DB. -2.5. Deprecation of 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, - or change examples to use ULA. Possible points to be re-written are - below. - - 2nd paragraph in RFC 3484 Section 3.1 describes scope comparison - mechanism. - - RFC 3484 Section 10 contains examples for site-local address. - -2.6. Private IPv4 address scope +2.3. Private IPv4 address scope As detailed in Remi's draft [I-D.denis-v6ops-nat-addrsel], when a host is in NATed site, and has a private IPv4 address and transitional addresses like 6to4 and Teredo, the host chooses transitional IPv6 address to access most of the dual-stack servers. This is because private IPv4 address is defined to be site-local scope, and as in RFC 3484, the scope matching rules (Rule 2) set lower priority for private IPv4 address. By changing the address scope of private IPv4 address to global, this problem can be solved. Considering the widely deployed NAT with IPv4 private address model, this change works in most of the cases. If not, this behavior can be overridden by configuring policy table, or by configuring routing table on a host. Moreover, some modern OSs have already implemented this change. -3. Conclusion - - This document lists several issues that should be included in the - revision of RFC 3484, which are useful universally and do no harm in - reasonable network environments. - - As the deployment of IPv6 progresses, the role of the address - selection mechanism is getting more important. This situation - revealed several important issues about the current address selection - rules. +2.4. Deprecation of site-local unicast address - It is much anticipated to provide the solutions for these issues. - Part of them, which are common issues for most of the reasonable - environment, should be done by updating the default address selection - rules as stated in this document, and the lest of them should be done - on per site basis by configuring the policy table manually, or using - the proposed policy updating mechanism. + RFC3484 contains a few "site-local unicast" and "fec::" description. + It's better to remove examples related to site-local unicast address, + or change examples to use ULA. Possible points to be re-written are + below. + - 2nd paragraph in RFC 3484 Section 3.1 describes scope comparison + mechanism. + - RFC 3484 Section 10 contains examples for site-local address. -4. Security Considerations +3. Security Considerations No security risk is found that degrades RFC 3484. -5. IANA Considerations +4. IANA Considerations Address type number for the policy table may have to be assigned by IANA. -6. References +5. References -6.1. Normative References +5.1. Normative References [I-D.denis-v6ops-nat-addrsel] Denis-Courmont, R., "Problems with IPv6 source address selection and IPv4 NATs", draft-denis-v6ops-nat-addrsel-00 (work in progress), February 2009. [I-D.ietf-ipv6-ula-central] Hinden, R., "Centrally Assigned Unique Local IPv6 Unicast Addresses", draft-ietf-ipv6-ula-central-02 (work in progress), June 2007. @@ -446,40 +284,115 @@ [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)", RFC 4380, February 2006. [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. -6.2. 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.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. Appendix A. Acknowledgements 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 inputs. -Appendix B. Revision History +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 + transitional mechanisms, the connectivity of them are recently + known to be worse than IPv4. These mechiansms are said to be the + last resort access to IPv6 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. + +B.3. Deprecated address + + Discussion: These addresses was removed from the current + specification. So, it 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 + especially in outdated implementations and bad effects brought by + them, however, it should be labeled differently from the + legitimate address blocks. + keep this entry for the sake of backward compatibility ? + +B.4. The longest match rule + + 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 two or more destination addresses are acquired from one FQDN, + 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. + + Regarding this problem, there was discussion in IETF and other places + like below. + + Discussion: The 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 may not worth the adverse effect of + disalbing the DNS based load balance technique. + +Appendix C. Revision History + + 01: + Re-structured to contain only the actual changes to RFC 3484. 00: Published as a 6man working group item. 03: Added acknowledgements. Added longest matching algorithm malfunction regarding local DNS round robin. The proposed changes section was re-structured. The issue of 6to4/Teredo and IPv4 prioritization was included.