INTERNET-DRAFT R. Hinden, Nokia June 23, 2004 B. Haberman, Caspian Unique Local IPv6 Unicast Addresses Status of this Memo By submitting this Internet-Draft, we certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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 a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This internet draft expires on November 28, 2004. Abstract This document defines an IPv6 unicast address format that is globally unique and is intended for local communications, usually inside of a site. They are not expected to be routable on the global Internet. draft-ietf-ipv6-unique-local-addr-05.txt [Page 1] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 Table of Contents 1.0 Introduction....................................................2 2.0 Acknowledgments.................................................3 3.0 Local IPv6 Unicast Addresses....................................3 3.1 Format..........................................................3 3.1.1 Background....................................................4 3.2 Global ID.......................................................4 3.2.1 Locally Assigned Global IDs...................................5 3.2.2 Sample Code for Pseudo-Random Global ID Algorithm.............6 3.2.3 Analysis of the Uniqueness of Global IDs......................6 3.3 Scope Definition................................................7 4.0 Routing.........................................................7 5.0 Renumbering and Site Merging....................................8 6.0 Site Border Router and Firewall Packet Filtering................8 7.0 DNS Issues......................................................8 8.0 Application and Higher Level Protocol Issues....................9 9.0 Use of Local IPv6 Addresses for Local Communications............9 10.0 Use of Local IPv6 Addresses with VPNs.........................10 11.0 Advantages and Disadvantages..................................11 12.0 Security Considerations.......................................11 13.0 IANA Considerations...........................................12 14.0 References....................................................12 14.1 Normative References..........................................12 14.2 Informative References........................................13 15.0 Authors' Addresses............................................13 16.0 Change Log....................................................14 1.0 Introduction This document defines an IPv6 unicast address format that is globally unique and is intended for local communications [IPV6]. These addresses are called Unique Local IPv6 Unicast Addresses and are abbreviated in this document as Local IPv6 addresses. They are not expected to be routable on the global Internet. They are routable inside of a more limited area such as a site. They may also be routed between a limited set of sites. Local IPv6 unicast addresses have the following characteristics: - Globally unique prefix. - Well known prefix to allow for easy filtering at site boundaries. - Allows sites to be combined or privately interconnected without creating any address conflicts or requiring renumbering of interfaces using these prefixes. - Internet Service Provider independent and can be used for draft-ietf-ipv6-unique-local-addr-05.txt [Page 2] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 communications inside of a site without having any permanent or intermittent Internet connectivity. - If accidentally leaked outside of a site via routing or DNS, there is no conflict with any other addresses. - In practice, applications may treat these addresses like global scoped addresses. This document defines the format of Local IPv6 addresses, how to allocate them, and usage considerations including routing, site border routers, DNS, application support, VPN usage, and guidelines for how to use for local communication inside a site. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119]. 2.0 Acknowledgments The underlying idea of creating Local IPv6 addresses described in this document been proposed a number of times by a variety of people. The authors of this draft do not claim exclusive credit. Credit goes to Brian Carpenter, Christian Huitema, Aidan Williams, Andrew White, Charlie Perkins, and many others. The authors would also like to thank Brian Carpenter, Charlie Perkins, Harald Alvestrand, Keith Moore, Margaret Wasserman, Shannon Behrens, Alan Beard, Hans Kruse, Geoff Huston, Pekka Savola, Christian Huitema, and Tim Chown for their comments and suggestions on this document. 3.0 Local IPv6 Unicast Addresses 3.1 Format The Local IPv6 addresses are created using a pseudo-randomly allocated global ID. They have the following format: | 7 bits | 41 bits | 16 bits | 64 bits | +--------+------------+-----------+-----------------------------+ | prefix | global ID | subnet ID | interface ID | +--------+------------+-----------+-----------------------------+ Where: prefix FC00::/7 prefix to identify Local IPv6 unicast addresses. global ID 41-bit global identifier used to create a draft-ietf-ipv6-unique-local-addr-05.txt [Page 3] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 globally unique prefix. See section 3.2 for additional information. subnet ID 16-bit subnet ID is an identifier of a subnet within the site. interface ID 64-bit interface ID as defined in [ADDARCH]. 3.1.1 Background There were a range of choices available when choosing the size of the prefix and global ID field length. There is a direct tradeoff between having a global ID field large enough to support foreseeable future growth and not using too much of the IPv6 address space needlessly. A reasonable way of evaluating a specific field length is to compare it to a projected 2050 world population of 9.3 billion [POPUL] and the number of resulting /48 prefixes per person. A range of prefix choices is shown in the following table: Prefix Global ID Number of Prefixes % of IPv6 Length /48 Prefixes per Person Address Space /11 37 137,438,953,472 15 0.049% /10 38 274,877,906,944 30 0.098% /9 39 549,755,813,888 59 0.195% /8 40 1,099,511,627,776 118 0.391% /7 41 2,199,023,255,552 236 0.781% /6 42 4,398,046,511,104 473 1.563% A very high utilization ratio of these allocations can be assumed because the global ID field does not require internal structure, and there is no reason to be able to aggregate the prefixes. The authors believe that a /7 prefix resulting in a 41 bit global ID is a good choice. It provides for a large number of assignments (i.e., 2.2 trillion) and at the same time uses less than .8% of the total IPv6 address space. It is unlikely that this space will be exhausted. If more than this were to be needed, then additional IPv6 address space could be allocated for this purpose. 3.2 Global ID The allocation of global IDs should be pseudo-random [RANDOM]. They should not be assigned sequentially or with well known numbers. This is to ensure that there is not any relationship between allocations and to help clarify that these prefixes are not intended to be routed draft-ietf-ipv6-unique-local-addr-05.txt [Page 4] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 globally. Specifically, these prefixes are designed to not aggregate. There are two ways to allocate Global IDs. These are centrally by a allocation authority and locally by the site. The Global ID is split into two parts for each type of allocation. The prefixes for each type are: FC00::/8 Centrally assigned FD00::/8 Locally assigned Each results in a 40-bit space to allocate. Two assignment methods are included because they have different properties. The centrally assigned global IDs are uniquely assigned. The local assignments are self generated and do not need any central coordination or assignment, but have a lower (but still adequate) probability of being unique. It is expected that large managed sites will prefer central assignments and small or disconnected sites will prefer local assignments. It is recommended that sites planning to use Local IPv6 addresses for extensive inter-site communication, initially or as a future possibility, use a centrally assigned prefix as there is no possibility of assignment conflicts. Sites are free to choose either approach. This document only allocates the prefix (FC00::/8) for centrally assigned local IPv6 addresses. The characteristics and technical allocation requirements for centrally assigned Local IPv6 addresses will be defined in a separate document. 3.2.1 Locally Assigned Global IDs Global IDs can be generated locally by an individual site. This makes it easy to get a prefix without the need to contact an assignment authority or internet service provider. There is not as high a degree of assurance that the prefix will not conflict with another locally generated prefix, but the likelihood of conflict is small. Sites that are not comfortable with this degree of uncertainty should use a centrally assigned global ID. Locally assigned global IDs MUST be generated with a pseudo-random algorithm consistent with [RANDOM]. Section 3.2.2 describes a suggested algorithm. It is important to ensure a reasonable likelihood uniqueness that all sites generating a Global IDs use a functionally similar algorithm. The use of a pseudo-random algorithm to generate global IDs in the draft-ietf-ipv6-unique-local-addr-05.txt [Page 5] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 locally assigned prefix gives an assurance that any network numbered using such a prefix is highly unlikely to have that address space clash with any other network that has another locally assigned prefix allocated to it. This is a particularly useful property when considering a number of scenarios including networks that merge, overlapping VPN address space, or hosts mobile between such networks. 3.2.2 Sample Code for Pseudo-Random Global ID Algorithm The algorithm described below is intended to be used for locally assigned Global IDs. In each case the resulting global ID will be used in the appropriate prefix as defined in section 3.2. 1) Obtain the current time of day in 64-bit NTP format [NTP]. 2) Obtain an EUI-64 identifier from the system running this algorithm. If an EUI-64 does not exist, one can be created from a 48-bit MAC address as specified in [ADDARCH]. If an EUI-64 cannot be obtained or created, a suitably unique identifier, local to the node, should be used (e.g. system serial number). 3) Concatenate the time of day with the system-specific identifier creating a key. 4) Compute an MD5 digest on the key as specified in [MD5DIG]. 5) Use the least significant 40 bits as the Global ID. This algorithm will result in a global ID that is reasonably unique and can be used as a Global ID. 3.2.3 Analysis of the Uniqueness of Global IDs The selection of a pseudo random global ID is similar to the selection of an SSRC identifier in RTP/RTCP defined in section 8.1 of [RTP]. This analysis is adapted from that document. Since the global ID is chosen randomly, it is possible that two or more networks that have an inter-network connection using globally- unique local addresses will chose the same global ID. The probability of collision can be approximated based on the number of connections between networks using globally-unique local addresses and the length of the ID (40 bits). The formula P = 1 - exp(-N**2 / 2**(L+1)) approximates the probability of collision (where N is the number connections and L is the length of the global ID). The following table shows the probability of a collision for a range draft-ietf-ipv6-unique-local-addr-05.txt [Page 6] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 of connections using a 40 bit global ID field. Connections Probability of Collision 2 1.81*10^-12 10 4.54*10^-11 100 4.54*10^-09 1000 4.54*10^-07 10000 4.54*10^-05 Based on this analysis the uniqueness of locally generated global IDs is adequate for sites planning a small to moderate amount of inter- site communication using locally generated global IDs. Sites planning more extensive inter-site communication should consider using the centrally assigned global ID. 3.3 Scope Definition By default, the scope of these addresses is global. That is, they are not limited by ambiguity like the site-local addresses defined in [ADDARCH]. Rather, these prefixes are globally unique, and as such, their applicability is greater than site-local addresses. Their limitation is in the routability of the prefixes, which is limited to a site and any explicit routing agreements with other sites to propagate them. Also, unlike site-locals, a site may have more than one of these prefixes and use them at the same time. 4.0 Routing Local IPv6 addresses are designed to be routed inside of a site in the same manner as other types of unicast addresses. They can be carried in any IPv6 routing protocol without any change. It is expected that they would share the same subnet IDs with provider based global unicast addresses if they were being used concurrently [GLOBAL]. Any router that is used between sites must be configured to filter out any incoming or outgoing Local IPv6 unicast routes. The exception to this is if specific /48 IPv6 local unicast routes have been configured to allow for inter-site communication. If BGP is being used at the site border with an ISP, the default BGP configuration must be set to to keep any Local IPv6 address prefixes from being advertised outside of the site or for these prefixes to be learned from another site. The exception to this is if there are draft-ietf-ipv6-unique-local-addr-05.txt [Page 7] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 specific /48 routes created for one or more Local IPv6 prefixes. 5.0 Renumbering and Site Merging The use of Local IPv6 addresses in a site results in making communication using these addresses independent of renumbering a site's provider based global addresses. When merging multiple sites none of the addresses created with these prefixes need to be renumbered because all of the addresses are unique. Routes for each specific prefix would have to be configured to allow routing to work correctly between the formerly separate sites. 6.0 Site Border Router and Firewall Packet Filtering While no serious harm will be done if packets with these addresses are sent outside of a site via a default route, it is recommended that routers be configured by default to keep any packets with Local IPv6 destination addresses from leaking outside of the site and to keep any site prefixes from being advertised outside of their site. Site border routers should install a "reject" route for the Local IPv6 prefix FC00::/7. This will ensure that packets with Local IPv6 destination addresses will not be forwarded outside of the site via a default route. Site border routers should respond with the appropriate ICMPv6 Destination Unreachable message to inform the source that the packet was not forwarded [ICMPV6]. This feedback is important to avoid transport protocol timeouts. Site border routers and firewalls should not forward any packets with Local IPv6 source or destination addresses outside of the site unless they have been explicitly configured with routing information about specific /48 Local IPv6 prefixes. The default behavior of these devices should be to install a "reject" route for these prefixes. Site border routers should respond with the appropriate ICMPv6 Destination Unreachable message to inform the source that the packet was not forwarded. Routers that maintain peering arrangements between Autonomous Systems throughout the Internet should obey the recommendations for site border routers unless configured otherwise. draft-ietf-ipv6-unique-local-addr-05.txt [Page 8] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 7.0 DNS Issues AAAA and PTR records for Local IPv6 addresses may be installed in the global DNS at the option of the site to which they are assigned. It is expected that most sites will not make use of this option, but some sites may find benefits in doing so. If Local IPv6 address are configured in the global DNS, no harm is done because they are unique and will not create any confusion. They may not be reachable, but this is a property that is common to all types of global IPv6 unicast addresses. 8.0 Application and Higher Level Protocol Issues Application and other higher level protocols can treat Local IPv6 addresses in the same manner as other types of global unicast addresses. No special handling is required. This type of addresses may not be reachable, but that is no different from other types of IPv6 global unicast addresses. Applications need to be able to handle multiple addresses that may or may not be reachable any point in time. In most cases this complexity should be hidden in APIs. From a host's perspective this difference shows up as different reachability than global unicast and could be handled by default that way. In some cases it is better for nodes and applications to treat them differently from global unicast addresses. A starting point might be to give them preference over global unicast, but fall back to global unicast if a particular destination is found to be unreachable. Much of this behavior can be controlled by how they are allocated to nodes and put into the DNS. However it is useful if a host can have both types of addresses and use them appropriately. Note that the address selection mechanisms of [ADDSEL], and in particular the policy override mechanism replacing default address selection, are expected to be used on a site where Local IPv6 addresses are configured. 9.0 Use of Local IPv6 Addresses for Local Communications Local IPv6 addresses, like global scope unicast addresses, are only assigned to nodes if their use has been enabled (via IPv6 address autoconfiguration [ADDAUTO], DHCPv6 [DHCP6], or manually). They are not created automatically the way that IPv6 link-local addresses are and will not appear or be used unless they are purposely configured. In order for hosts to autoconfigure Local IPv6 addresses, routers draft-ietf-ipv6-unique-local-addr-05.txt [Page 9] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 have to be configured to advertise Local IPv6 /64 prefixes in router advertisements, or a DHCPv6 server must have been configured to assign them. In order for a node to learn the Local IPv6 address of another node, the Local IPv6 address must have been installed in the DNS or another naming system. For these reasons, it is straight forward to control their usage in a site. To limit the use of Local IPv6 addresses the following guidelines apply: - Nodes that are to only be reachable inside of a site: The local DNS should be configured to only include the Local IPv6 addresses of these nodes. Nodes with only Local IPv6 addresses must not be installed in the global DNS. - Nodes that are to be limited to only communicate with other nodes in the site: These nodes should be set to only autoconfigure Local IPv6 addresses via [ADDAUTO] or to only receive Local IPv6 addresses via [DHCP6]. Note: For the case where both global and Local IPv6 prefixes are being advertised on a subnet, this will require a switch in the devices to only autoconfigure Local IPv6 addresses. - Nodes that are to be reachable from inside of the site and from outside of the site: The DNS should be configured to include the global addresses of these nodes. The local DNS may be configured to also include the Local IPv6 addresses of these nodes. - Nodes that can communicate with other nodes inside of the site and outside of the site: These nodes should autoconfigure global addresses via [ADDAUTO] or receive global address via [DHCP6]. They may also obtain Local IPv6 addresses via the same mechanisms. 10.0 Use of Local IPv6 Addresses with VPNs Local IPv6 addresses can be used for inter-site Virtual Private Networks (VPN) if appropriate routes are set up. Because the addresses are unique these VPNs will work reliably and without the need for translation. They have the additional property that they will continue to work if the individual sites are renumbered or merged. draft-ietf-ipv6-unique-local-addr-05.txt [Page 10] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 11.0 Advantages and Disadvantages 11.1 Advantages This approach has the following advantages: - Provides Local IPv6 prefixes that can be used independently of any provider based IPv6 unicast address allocations. This is useful for sites not always connected to the Internet or sites that wish to have a distinct prefix that can be used to localize traffic inside of the site. - Applications can treat these addresses in an identical manner as any other type of global IPv6 unicast addresses. - Sites can be merged without any renumbering of the Local IPv6 addresses. - Sites can change their provider based IPv6 unicast address without disrupting any communication using Local IPv6 addresses. - Well known prefix that allows for easy filtering at site boundary. - Can be used for inter-site VPNs. - If accidently leaked outside of a site via routing or DNS, there is no conflict with any other addresses. 11.2 Disadvantages This approach has the following disadvantages: - Not possible to route Local IPv6 prefixes on the global Internet with current routing technology. Consequentially, it is necessary to have the default behavior of site border routers to filter these addresses. - There is a very low probability of non-unique locally assigned global IDs being generated by the algorithm in section 3.2.3. This risk can be ignored for all practical purposes, but it leads to a theoretical risk of clashing address prefixes. 12.0 Security Considerations Local IPv6 addresses do not provide any inherent security to the nodes that use them. They may be used with filters at site boundaries to keep Local IPv6 traffic inside of the site, but this is no more or less secure than filtering any other type of global IPv6 unicast addresses. Local IPv6 addresses do allow for address-based security mechanisms, including IPSEC, across end to end VPN connections. draft-ietf-ipv6-unique-local-addr-05.txt [Page 11] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 13.0 IANA Considerations The IANA is instructed to assign the FC00::/7 prefix for Unique Local IPv6 unicast addresses. The prefix is divided in half for the following purposes: FC00::/8 Centrally assigned FD00::/8 Locally assigned The IANA is instructed to reserve the prefix FC00::/8 for Centrally assigned Unique Local IPv6 unicast addresses. The FD00::/8 prefix is defined in this specification for Locally assigned Unique Local IPv6 unicast addresses. 14.0 References 14.1 Normative References [ADDARCH] Hinden, R., S. Deering, S., "IP Version 6 Addressing Architecture", RFC 3515, April 2003. [GLOBAL] Hinden, R., S. Deering, E. Nordmark, "IPv6 Global Unicast Address Format", RFC 3587, August 2003. [ICMPV6] Conta, A., S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC2463, December 1998. [IPV6] Deering, S., R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [MD5DIG] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [NTP] Mills, David L., "Network Time Protocol (Version 3) Specification, Implementation and Analysis", RFC 1305, March 1992. [POPUL] Population Reference Bureau, "World Population Data Sheet of the Population Reference Bureau 2002", August 2002. [RANDOM] Eastlake, D. 3rd, S. Crocker, J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994. draft-ietf-ipv6-unique-local-addr-05.txt [Page 12] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP14, March 1997. 14.2 Informative References [ADDAUTO] Thomson, S., T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [ADDSEL] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. [DHCP6] Droms, R., et. al., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC3315, July 2003. [RTP] Schulzrinne, H., S. Casner, R. Frederick, V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications" RFC3550, July 2003. 15.0 Authors' Addresses Robert M. Hinden Nokia 313 Fairchild Drive Mountain View, CA 94043 USA phone: +1 650 625-2004 email: bob.hinden@nokia.com Brian Haberman Caspian Networks 1 Park Drive, Suite 300 Research Triangle Park, NC 27709 USA phone: +1-929-949-4828 email: brian@innovationslab.net draft-ietf-ipv6-unique-local-addr-05.txt [Page 13] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 16.0 Change Log Draft o Removed the definition and technical requirements for centrally assigned local address. The Centrally assigned local addresses will be defined in a separate document. This document defines the specific prefixes to be used for centrally and locally assigned IPv6 local addresses, but only the locally assigned local addresses are defined here. Draft o Clarified text in section 3.2.1 that central assigned prefixes should be assigned under the authority of a single allocation organization. o Added step to suggested pseudo-random algorithm that in the case of centrally assigned prefixes the computed global IDs should be verified against the escrow. o Added new text to section 3.2.2 that explains in more detail the need for pseudo-random global IDs (i.e., avoid duplicate allocations). o Rewrote section 7.0 to describe DNS AAAA and PTR records, and clarify when they might be installed in the global DNS. o Various editorial changes. Draft o Removed requirement of a fee per central allocation and updated IANA considerations to reflect this. Rewrote text to focus on the requirement to avoid hoarding of allocations. o Changed "filtering" and "black hole routes" to "reject" routes. o Changed uppers case requirements (i.e., MUST, SHOULD, etc.) to lower case in sections giving operational advice. o Removed paragraph mentioning "Multicast DNS". o Various editorial changes. Draft o Removed mention of 10 euro charge and changed text in section 3.2.1 and IANA considerations to restate the requirement for low cost allocations and added specific requirement to prevent hording. o Added need to send ICMPv6 destination unreachable messages if packets are filtered or dropped at site boundaries. o Changed format section to list prefix sizes and definition, and changed discussion of prefix sizes to new background section. o Various editorial changes. draft-ietf-ipv6-unique-local-addr-05.txt [Page 14] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 Draft o Removed example of PIR as an example of an allocation authority and clarified the text that the IANA should delegate the centrally assigned prefix to an allocation authority. o Changed sample code for generating pseudo random Global IDs to not require any human input. Changes from using birthday to unique token (e.g., EUI-64, serial number, etc.) available on machine running the algorithm. o Added a new section analyzing the uniqueness properties of the pseudo random number algorithm. o Added text to recommend that centrally assigned local addresses be used for site planning extensive inter-site communication. o Clarified that domain border routers should follow site border router recommendations. o Clarified that AAAA DNS records should not be installed in the global DNS. o Several editorial changes. Draft o Changed file name to become an IPv6 w.g. group document. o Clarified language in Routing and Firewall sections. o Several editorial changes. Draft o Changed title and name of addresses defined in this document to "Unique Local IPv6 Unicast Addresses" with abbreviation of "Local IPv6 addresses". o Several editorial changes. Draft o Added section on scope definition and updated application requirement section. o Clarified that, by default, the scope of these addresses is global. o Renumbered sections and general text improvements o Removed reserved global ID values o Added pseudo code for local allocation submitted by Brian Haberman and added him as an author. o Split Global ID values into centrally assigned and local assignments and added text to describe local assignments draft-ietf-ipv6-unique-local-addr-05.txt [Page 15] INTERNET-DRAFT Unique Local IPv6 Unicast Addresses June 2004 Draft o Initial Draft draft-ietf-ipv6-unique-local-addr-05.txt [Page 16]