900 lines
35 KiB
Plaintext
900 lines
35 KiB
Plaintext
|
||
|
||
|
||
|
||
|
||
|
||
Network Working Group R. Hinden
|
||
Request for Comments: 4193 Nokia
|
||
Category: Standards Track B. Haberman
|
||
JHU-APL
|
||
October 2005
|
||
|
||
|
||
Unique Local IPv6 Unicast Addresses
|
||
|
||
Status of This Memo
|
||
|
||
This document specifies an Internet standards track protocol for the
|
||
Internet community, and requests discussion and suggestions for
|
||
improvements. Please refer to the current edition of the "Internet
|
||
Official Protocol Standards" (STD 1) for the standardization state
|
||
and status of this protocol. Distribution of this memo is unlimited.
|
||
|
||
Copyright Notice
|
||
|
||
Copyright (C) The Internet Society (2005).
|
||
|
||
Abstract
|
||
|
||
This document defines an IPv6 unicast address format that is globally
|
||
unique and is intended for local communications, usually inside of a
|
||
site. These addresses are not expected to be routable on the global
|
||
Internet.
|
||
|
||
Table of Contents
|
||
|
||
1. Introduction ....................................................2
|
||
2. Acknowledgements ................................................3
|
||
3. 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 ...5
|
||
3.2.3. Analysis of the Uniqueness of Global IDs ............6
|
||
3.3. Scope Definition ...........................................6
|
||
4. Operational Guidelines ..........................................7
|
||
4.1. Routing ....................................................7
|
||
4.2. Renumbering and Site Merging ...............................7
|
||
4.3. Site Border Router and Firewall Packet Filtering ...........8
|
||
4.4. DNS Issues .................................................8
|
||
4.5. Application and Higher Level Protocol Issues ...............9
|
||
4.6. Use of Local IPv6 Addresses for Local Communication ........9
|
||
4.7. Use of Local IPv6 Addresses with VPNs .....................10
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 1]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
5. Global Routing Considerations ..................................11
|
||
5.1. From the Standpoint of the Internet .......................11
|
||
5.2. From the Standpoint of a Site .............................11
|
||
6. Advantages and Disadvantages ...................................12
|
||
6.1. Advantages ................................................12
|
||
6.2. Disadvantages .............................................13
|
||
7. Security Considerations ........................................13
|
||
8. IANA Considerations ............................................13
|
||
9. References .....................................................13
|
||
9.1. Normative References ......................................13
|
||
9.2. Informative References ....................................14
|
||
|
||
1. 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 (with high probability of uniqueness).
|
||
|
||
- Well-known prefix to allow for easy filtering at site
|
||
boundaries.
|
||
|
||
- Allow sites to be combined or privately interconnected without
|
||
creating any address conflicts or requiring renumbering of
|
||
interfaces that use these prefixes.
|
||
|
||
- Internet Service Provider independent and can be used for
|
||
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.
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 2]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
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 [RFC2119].
|
||
|
||
2. Acknowledgements
|
||
|
||
The underlying idea of creating Local IPv6 addresses described in
|
||
this document has been proposed a number of times by a variety of
|
||
people. The authors of this document 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, Tim
|
||
Chown, Steve Bellovin, Alex Zinin, Tony Hain, Bill Fenner, Sam
|
||
Hartman, and Elwyn Davies for their comments and suggestions on this
|
||
document.
|
||
|
||
3. 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 |1| 40 bits | 16 bits | 64 bits |
|
||
+--------+-+------------+-----------+----------------------------+
|
||
| Prefix |L| Global ID | Subnet ID | Interface ID |
|
||
+--------+-+------------+-----------+----------------------------+
|
||
|
||
Where:
|
||
|
||
Prefix FC00::/7 prefix to identify Local IPv6 unicast
|
||
addresses.
|
||
|
||
L Set to 1 if the prefix is locally assigned.
|
||
Set to 0 may be defined in the future. See
|
||
Section 3.2 for additional information.
|
||
|
||
Global ID 40-bit global identifier used to create a
|
||
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].
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 3]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
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
|
||
space (including the L bit) 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 is pseudo-random [RANDOM]. They MUST
|
||
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
|
||
globally. Specifically, these prefixes are not designed to
|
||
aggregate.
|
||
|
||
This document defines a specific local method to allocate Global IDs,
|
||
indicated by setting the L bit to 1. Another method, indicated by
|
||
clearing the L bit, may be defined later. Apart from the allocation
|
||
method, all Local IPv6 addresses behave and are treated identically.
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 4]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
The local assignments are self-generated and do not need any central
|
||
coordination or assignment, but have an extremely high probability of
|
||
being unique.
|
||
|
||
3.2.1. Locally Assigned Global IDs
|
||
|
||
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 that all sites generating
|
||
Global IDs use a functionally similar algorithm to ensure there is a
|
||
high probability of uniqueness.
|
||
|
||
The use of a pseudo-random algorithm to generate Global IDs in the
|
||
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
|
||
in order to create a key.
|
||
|
||
4) Compute an SHA-1 digest on the key as specified in [FIPS, SHA1];
|
||
the resulting value is 160 bits.
|
||
|
||
5) Use the least significant 40 bits as the Global ID.
|
||
|
||
6) Concatenate FC00::/7, the L bit set to 1, and the 40-bit Global
|
||
ID to create a Local IPv6 address prefix.
|
||
|
||
This algorithm will result in a Global ID that is reasonably unique
|
||
and can be used to create a locally assigned Local IPv6 address
|
||
prefix.
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 5]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
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 Global IDs are chosen randomly (and independently), it is
|
||
possible that separate networks have chosen the same Global ID. For
|
||
any given network, with one or more random Global IDs, that has
|
||
inter-connections to other such networks, having a total of N such
|
||
IDs, the probability that two or more of these IDs will collide can
|
||
be approximated using the formula:
|
||
|
||
P = 1 - exp(-N**2 / 2**(L+1))
|
||
|
||
where P is the probability of collision, N is the number of
|
||
interconnected Global IDs, and L is the length of the Global ID.
|
||
|
||
The following table shows the probability of a collision for a range
|
||
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.
|
||
|
||
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 see Section 4.1). Also, unlike site-locals, a
|
||
site may have more than one of these prefixes and use them at the
|
||
same time.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 6]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
4. Operational Guidelines
|
||
|
||
The guidelines in this section do not require any change to the
|
||
normal routing and forwarding functionality in an IPv6 host or
|
||
router. These are configuration and operational usage guidelines.
|
||
|
||
4.1. 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].
|
||
|
||
The default behavior of exterior routing protocol sessions between
|
||
administrative routing regions must be to ignore receipt of and not
|
||
advertise prefixes in the FC00::/7 block. A network operator may
|
||
specifically configure prefixes longer than FC00::/7 for inter-site
|
||
communication.
|
||
|
||
If BGP is being used at the site border with an ISP, the default BGP
|
||
configuration must filter out any Local IPv6 address prefixes, both
|
||
incoming and outgoing. It must be set both to keep any Local IPv6
|
||
address prefixes from being advertised outside of the site as well as
|
||
to keep these prefixes from being learned from another site. The
|
||
exception to this is if there are specific /48 or longer routes
|
||
created for one or more Local IPv6 prefixes.
|
||
|
||
For link-state IGPs, it is suggested that a site utilizing IPv6 local
|
||
address prefixes be contained within one IGP domain or area. By
|
||
containing an IPv6 local address prefix to a single link-state area
|
||
or domain, the distribution of prefixes can be controlled.
|
||
|
||
4.2. Renumbering and Site Merging
|
||
|
||
The use of Local IPv6 addresses in a site results in making
|
||
communication that uses these addresses independent of renumbering a
|
||
site's provider-based global addresses.
|
||
|
||
When merging multiple sites, the addresses created with these
|
||
prefixes are unlikely to need to be renumbered because all of the
|
||
addresses have a high probability of being unique. Routes for each
|
||
specific prefix would have to be configured to allow routing to work
|
||
correctly between the formerly separate sites.
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 7]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
4.3. 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 addresses from leaking outside of the site and to keep any site
|
||
prefixes from being advertised outside of their site.
|
||
|
||
Site border routers and firewalls should be configured to 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 or longer Local IPv6 prefixes. This
|
||
will ensure that packets with Local IPv6 destination addresses will
|
||
not be forwarded outside of the site via a default route. 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. [ICMPV6]. This feedback is
|
||
important to avoid transport protocol timeouts.
|
||
|
||
Routers that maintain peering arrangements between Autonomous Systems
|
||
throughout the Internet should obey the recommendations for site
|
||
border routers, unless configured otherwise.
|
||
|
||
4.4. DNS Issues
|
||
|
||
At the present time, AAAA and PTR records for locally assigned local
|
||
IPv6 addresses are not recommended to be installed in the global DNS.
|
||
|
||
For background on this recommendation, one of the concerns about
|
||
adding AAAA and PTR records to the global DNS for locally assigned
|
||
Local IPv6 addresses stems from the lack of complete assurance that
|
||
the prefixes are unique. There is a small possibility that the same
|
||
locally assigned IPv6 Local addresses will be used by two different
|
||
organizations both claiming to be authoritative with different
|
||
contents. In this scenario, it is likely there will be a connection
|
||
attempt to the closest host with the corresponding locally assigned
|
||
IPv6 Local address. This may result in connection timeouts,
|
||
connection failures indicated by ICMP Destination Unreachable
|
||
messages, or successful connections to the wrong host. Due to this
|
||
concern, adding AAAA records for these addresses to the global DNS is
|
||
thought to be unwise.
|
||
|
||
Reverse (address-to-name) queries for locally assigned IPv6 Local
|
||
addresses MUST NOT be sent to name servers for the global DNS, due to
|
||
the load that such queries would create for the authoritative name
|
||
servers for the ip6.arpa zone. This form of query load is not
|
||
specific to locally assigned Local IPv6 addresses; any current form
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 8]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
of local addressing creates additional load of this kind, due to
|
||
reverse queries leaking out of the site. However, since allowing
|
||
such queries to escape from the site serves no useful purpose, there
|
||
is no good reason to make the existing load problems worse.
|
||
|
||
The recommended way to avoid sending such queries to nameservers for
|
||
the global DNS is for recursive name server implementations to act as
|
||
if they were authoritative for an empty d.f.ip6.arpa zone and return
|
||
RCODE 3 for any such query. Implementations that choose this
|
||
strategy should allow it to be overridden, but returning an RCODE 3
|
||
response for such queries should be the default, both because this
|
||
will reduce the query load problem and also because, if the site
|
||
administrator has not set up the reverse tree corresponding to the
|
||
locally assigned IPv6 Local addresses in use, returning RCODE 3 is in
|
||
fact the correct answer.
|
||
|
||
4.5. 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 address
|
||
may not be reachable, but that is no different from other types of
|
||
IPv6 global unicast address. Applications need to be able to handle
|
||
multiple addresses that may or may not be reachable at any point in
|
||
time. In most cases, this complexity should be hidden in APIs.
|
||
|
||
From a host's perspective, the difference between Local IPv6 and
|
||
other types of global unicast addresses shows up as different
|
||
reachability and could be handled by default in 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.
|
||
|
||
4.6. Use of Local IPv6 Addresses for Local Communication
|
||
|
||
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
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 9]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
not created automatically in 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
|
||
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 a
|
||
naming system (e.g., DNS, proprietary naming system, etc.) For these
|
||
reasons, controlling their usage in a site is straightforward.
|
||
|
||
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.
|
||
|
||
4.7. 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.
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 10]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
5. Global Routing Considerations
|
||
|
||
Section 4.1 provides operational guidelines that forbid default
|
||
routing of local addresses between sites. Concerns were raised to
|
||
the IPv6 working group and to the IETF as a whole that sites may
|
||
attempt to use local addresses as globally routed provider-
|
||
independent addresses. This section describes why using local
|
||
addresses as globally-routed provider-independent addresses is
|
||
unadvisable.
|
||
|
||
5.1. From the Standpoint of the Internet
|
||
|
||
There is a mismatch between the structure of IPv6 local addresses and
|
||
the normal IPv6 wide area routing model. The /48 prefix of an IPv6
|
||
local addresses fits nowhere in the normal hierarchy of IPv6 unicast
|
||
addresses. Normal IPv6 unicast addresses can be routed
|
||
hierarchically down to physical subnet (link) level and only have to
|
||
be flat-routed on the physical subnet. IPv6 local addresses would
|
||
have to be flat-routed even over the wide area Internet.
|
||
|
||
Thus, packets whose destination address is an IPv6 local address
|
||
could be routed over the wide area only if the corresponding /48
|
||
prefix were carried by the wide area routing protocol in use, such as
|
||
BGP. This contravenes the operational assumption that long prefixes
|
||
will be aggregated into many fewer short prefixes, to limit the table
|
||
size and convergence time of the routing protocol. If a network uses
|
||
both normal IPv6 addresses [ADDARCH] and IPv6 local addresses, these
|
||
types of addresses will certainly not aggregate with each other,
|
||
since they differ from the most significant bit onwards. Neither
|
||
will IPv6 local addresses aggregate with each other, due to their
|
||
random bit patterns. This means that there would be a very
|
||
significant operational penalty for attempting to use IPv6 local
|
||
address prefixes generically with currently known wide area routing
|
||
technology.
|
||
|
||
5.2. From the Standpoint of a Site
|
||
|
||
There are a number of design factors in IPv6 local addresses that
|
||
reduce the likelihood that IPv6 local addresses will be used as
|
||
arbitrary global unicast addresses. These include:
|
||
|
||
- The default rules to filter packets and routes make it very
|
||
difficult to use IPv6 local addresses for arbitrary use across
|
||
the Internet. For a site to use them as general purpose unicast
|
||
addresses, it would have to make sure that the default rules
|
||
were not being used by all other sites and intermediate ISPs
|
||
used for their current and future communication.
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 11]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
- They are not mathematically guaranteed to be unique and are not
|
||
registered in public databases. Collisions, while highly
|
||
unlikely, are possible and a collision can compromise the
|
||
integrity of the communications. The lack of public
|
||
registration creates operational problems.
|
||
|
||
- The addresses are allocated randomly. If a site had multiple
|
||
prefixes that it wanted to be used globally, the cost of
|
||
advertising them would be very high because they could not be
|
||
aggregated.
|
||
|
||
- They have a long prefix (i.e., /48) so a single local address
|
||
prefix doesn't provide enough address space to be used
|
||
exclusively by the largest organizations.
|
||
|
||
6. Advantages and Disadvantages
|
||
|
||
6.1. 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 that uses 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.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 12]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
6.2. 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.
|
||
|
||
7. 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.
|
||
|
||
8. IANA Considerations
|
||
|
||
The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
|
||
|
||
9. References
|
||
|
||
9.1. Normative References
|
||
|
||
[ADDARCH] Hinden, R. and S. Deering, "Internet Protocol Version 6
|
||
(IPv6) Addressing Architecture", RFC 3513, April 2003.
|
||
|
||
[FIPS] "Federal Information Processing Standards Publication",
|
||
(FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
|
||
|
||
[GLOBAL] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
|
||
Unicast Address Format", RFC 3587, August 2003.
|
||
|
||
[ICMPV6] Conta, A. and S. Deering, "Internet Control Message
|
||
Protocol (ICMPv6) for the Internet Protocol Version 6
|
||
(IPv6) Specification", RFC 2463, December 1998.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 13]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
|
||
(IPv6) Specification", RFC 2460, December 1998.
|
||
|
||
[NTP] Mills, D., "Network Time Protocol (Version 3)
|
||
Specification, Implementation and Analysis", RFC 1305,
|
||
March 1992.
|
||
|
||
[RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
|
||
"Randomness Requirements for Security", BCP 106, RFC 4086,
|
||
June 2005.
|
||
|
||
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
|
||
Requirement Levels", BCP 14, RFC 2119, March 1997.
|
||
|
||
[SHA1] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
|
||
(SHA1)", RFC 3174, September 2001.
|
||
|
||
9.2. Informative References
|
||
|
||
[ADDAUTO] Thomson, S. and 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., Bound, J., Volz, B., Lemon, T., Perkins, C., and
|
||
M. Carney, "Dynamic Host Configuration Protocol for IPv6
|
||
(DHCPv6)", RFC 3315, July 2003.
|
||
|
||
[POPUL] Population Reference Bureau, "World Population Data Sheet
|
||
of the Population Reference Bureau 2002", August 2002.
|
||
|
||
[RTP] Schulzrinne, H., Casner, S., Frederick, R., and V.
|
||
Jacobson, "RTP: A Transport Protocol for Real-Time
|
||
Applications", STD 64, RFC 3550, July 2003.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 14]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
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
|
||
Johns Hopkins University
|
||
Applied Physics Lab
|
||
11100 Johns Hopkins Road
|
||
Laurel, MD 20723
|
||
USA
|
||
|
||
Phone: +1 443 778 1319
|
||
EMail: brian@innovationslab.net
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 15]
|
||
|
||
RFC 4193 Unique Local IPv6 Unicast Addresses October 2005
|
||
|
||
|
||
Full Copyright Statement
|
||
|
||
Copyright (C) The Internet Society (2005).
|
||
|
||
This document is subject to the rights, licenses and restrictions
|
||
contained in BCP 78, and except as set forth therein, the authors
|
||
retain all their rights.
|
||
|
||
This document and the information contained herein are provided on an
|
||
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
|
||
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
|
||
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
|
||
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
|
||
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
|
||
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
||
|
||
Intellectual Property
|
||
|
||
The IETF takes no position regarding the validity or scope of any
|
||
Intellectual Property Rights or other rights that might be claimed to
|
||
pertain to the implementation or use of the technology described in
|
||
this document or the extent to which any license under such rights
|
||
might or might not be available; nor does it represent that it has
|
||
made any independent effort to identify any such rights. Information
|
||
on the procedures with respect to rights in RFC documents can be
|
||
found in BCP 78 and BCP 79.
|
||
|
||
Copies of IPR disclosures made to the IETF Secretariat and any
|
||
assurances of licenses to be made available, or the result of an
|
||
attempt made to obtain a general license or permission for the use of
|
||
such proprietary rights by implementers or users of this
|
||
specification can be obtained from the IETF on-line IPR repository at
|
||
http://www.ietf.org/ipr.
|
||
|
||
The IETF invites any interested party to bring to its attention any
|
||
copyrights, patents or patent applications, or other proprietary
|
||
rights that may cover technology that may be required to implement
|
||
this standard. Please address the information to the IETF at ietf-
|
||
ipr@ietf.org.
|
||
|
||
Acknowledgement
|
||
|
||
Funding for the RFC Editor function is currently provided by the
|
||
Internet Society.
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
Hinden & Haberman Standards Track [Page 16]
|
||
|