Network Working Group A. Matsumoto Internet-Draft T. Fujisaki Intended status: Standards Track NTT Expires: September 17, 2009 R. Hiromi Intec Netcore K. Kanayama INTEC Systems March 16, 2009 Things To Be Considered for RFC 3484 Revision draft-arifumi-6man-rfc3484-revise-01.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 17, 2009. Copyright Notice Matsumoto, et al. Expires September 17, 2009 [Page 1] Internet-Draft RFC3484 Revise March 2009 Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. 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. Matsumoto, et al. Expires September 17, 2009 [Page 2] Internet-Draft RFC3484 Revise March 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Problem Example . . . . . . . . . . . . . . . . . . . . . 4 2. Proposed Changes to RFC 3484 . . . . . . . . . . . . . . . . . 5 2.1. To remove site-local unicast address . . . . . . . . . . . 5 2.2. To change default policy table . . . . . . . . . . . . . . 6 2.3. To change ULA address scope to site-local . . . . . . . . 6 2.4. To add descriptions for source address selection for multicast packet . . . . . . . . . . . . . . . . . . . . . 7 2.5. To make address type dependent control possible . . . . . 7 2.6. To disable or restrict RFC 3484 Section 6 Rule 9 . . . . . 7 2.7. To change private IPv4 address scope . . . . . . . . . . . 8 3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Normative References . . . . . . . . . . . . . . . . . . . 9 6.2. Informative References . . . . . . . . . . . . . . . . . . 10 Appendix A. Appendix. Revision History . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Matsumoto, et al. Expires September 17, 2009 [Page 3] Internet-Draft RFC3484 Revise March 2009 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. 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 others should not. 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. Matsumoto, et al. Expires September 17, 2009 [Page 4] Internet-Draft RFC3484 Revise March 2009 +--------+ | 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 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. 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, or change examples to use ULA. Possible points to be re-written are below. - 2nd paragraph in Section 3.1 describes scope comparison mechanism. Matsumoto, et al. Expires September 17, 2009 [Page 5] Internet-Draft RFC3484 Revise March 2009 - 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. When we apply these changes, the default policy table looks like this. Prefix Precedence Label ::1/128 50 0 ::/0 30 2 2002::/16 20 3 ::ffff:0:0/96 10 4 2001::/32 5 5 (For Teredo) 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. 2.3. To change ULA address scope to site-local 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. Matsumoto, et al. Expires September 17, 2009 [Page 6] Internet-Draft RFC3484 Revise March 2009 2.4. To add descriptions for source address selection for multicast packet For example, we have to pay attention to source address selection for a multicast packet. 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. 2.5. 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 2.6. 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. Matsumoto, et al. Expires September 17, 2009 [Page 7] Internet-Draft RFC3484 Revise March 2009 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 a lot of 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 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. 2.7. To change 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 Matsumoto, et al. Expires September 17, 2009 [Page 8] Internet-Draft RFC3484 Revise March 2009 lower priority for private IPv4 address. By changing the address scope of private IPv4 address to global, this problem can be solved. 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 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 Matsumoto, et al. Expires September 17, 2009 [Page 9] Internet-Draft RFC3484 Revise March 2009 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.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.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-07 (work in progress), March 2009. [RFC3041] Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001. [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. Appendix A. Appendix. Revision History 01: The issue of private IPv4 address scope was added. The issue of ULA address scope was added. Discussion of longest matching rule was expanded. 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 Matsumoto, et al. Expires September 17, 2009 [Page 10] Internet-Draft RFC3484 Revise March 2009 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 Matsumoto, et al. Expires September 17, 2009 [Page 11]