One document matched: draft-ietf-ipngwg-linkname-00.txt
INTERNET-DRAFT D. Harrington
Internet Draft Digital Equipment Corp
Link Local Addressing and Name Resolution in IPv6
<draft-ietf-ipngwg-linkname-00.txt>
Abstract
This draft proposes an experimental mechanism by which IPv6 link-local
addresses and associated system names may be distributed among
interconnected hosts, for use by users and applications. It
provides an overview of the problem, a proposed solution (including
suggested protocol details), and lists various related issues.
This work is introduced to the IPng Working Group initially,
although it might also have implications or concerns relevant
to individuals working on directory services and other areas.
Status of this Memo
This document is a submission to the IPng Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the ipng@sunroof.eng.sun.com mailing list. This document is not
at this time a product of the IPng Working Group, but a proposal to
become a product of the IPng Working Group.
This document is an Internet-Draft. 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
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Distribution of this document is unlimited.
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Table of Contents:
1. Introduction.................................................3
2. Terminology and Definitions..................................3
3. Design Goals.................................................4
4. Proposed Protocol............................................4
4.1 Server Processing and Advertisements.....................4
4.2 Client Processing and Requests...........................5
5. Interaction with DNS and resolver routines...................7
6. Alternative uses.............................................7
7. Multilink issues.............................................7
8. Security Issues..............................................8
Acknowledgements.............................................9
References...................................................9
Author's Address.............................................9
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1. Introduction
One aspect of IP Version 6 which is somewhat novel is the "plug-
and-play" capability, in which a system may be interconnected with
other IPv6 systems without the need for formal configuration. In
particular, the use of autonomically created link-local addresses,
which are limited in scope to the physical link to which the
system is connected, is meant to support this goal. This is
sometimes referred to informally as the "dentist's office"
scenario. In fact, early experience at the interoperability
bakeoff at the University of New Hampshire this past February
(1996) showed that to a large degree this goal is achieved;
systems from multiple vendors were interconnected to an Ethernet,
and in the absence of any routers were able to communicate with
neighboring systems.
One capability which is lacking in this case, however, is a simple
name to address (and inverse) lookup function. While it is a
simple matter to add support to existing resolver routines to
support the lookup of IPv6 addresses from a local ASCII file (e.g.
/etc/hosts), it is extremely inconvenient to determine the link-
local addresses and names of all adjacent systems, and enter this
information into said file. Also, using a manual mechanism such
as this is error prone and may quickly become stale. Clearly, an
automated means of distributing this information is called for.
This draft proposes that an IPv6 systems, when utilizing an
interface which supports the link-local model, advertise its name
and associated link-local IPv6 address to a multicast group of
link-local scope, using a simple protocol over UDP. It also
allows a system to send a query for a particular name or address
to the group, which may be responded to by the system matching the
given item. The effects of multilink hosts, interactions with
name resolving services, and security concerns are discussed.
2. Terminology and Definitions
link - a communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer
immediately below IPv6. Examples are Ethernets (simple
or bridged); PPP links; X.25, Frame Relay, or ATM
networks; and internet (or higher) layer "tunnels",
such as tunnels over IPv4 or IPv6 itself.
neighbors - nodes attached to the same link.
interface - a node's attachment to a link.
link-local - An address formed during interface initialization,
address composed of the well known prefix FE80:: and a media
specific token. This address is limited in scope to
the link and may not be forwarded by a router.
resolver - A program which retrieves information from name servers
in response to client requests. It is typically
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available as a system or library call to a program.
Multilink - A system which has multiple link interfaces and multiple
IPv6 addresses. Note that the different interfaces may
or may not be connected to the same physical media, or
even the same media type.
3. Design Goals
The goal of this proposal is to provide a way to advertise and use
names and link local addresses among IPv6 hosts. It is also a
goal to keep this addressing information OUT of the DNS/BIND
server's data file, as it is almost impossible for such a server
to know if providing such an address is appropriate, without the
server having to keep much too much information about the relative
location of both the client system and the requested hostname.
The proposed protocol is deliberately simple and limited. It has
some elements in common with the Service Location protocol, and it
may be worth investigating the relationship between the two,
especially as Service Location adds support for IPv6. Finally,
the implementation of this mechanism will also serve to exercise
other elements IPv6 systems, in particular multicast support and
the BSD API interface. For these reasons it is requested that
this protocol be considered Experimental.
4. Proposed Protocol
There are two aspects to implementing a simple name to address
function: providing local name and address information (server),
and requesting and storing remote name or address information
(client). An IPv6 system SHOULD provide the server functionality,
in order to distribute its own information to others. A system
MAY wish to be a client, in order to learn and use the information
of neighbors.
In order to participate in this service, a system must join the
IPv6 multicast group FF02::<TBD>, which has link-local scope. The
UDP port <TBD> is reserved for use of this protocol.
4.1 Server Processing and Advertisements
A system SHOULD advertise its system name (non-fully qualified,
i.e. no domains, just a simple hostname) and the associated link
local address over each of its interfaces, along with an
indication of how long the information should be considered valid.
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3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | A D V |R e s e r v e d| L E N G T H |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S e q u e n c e N u m b e r | T T L |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Simple hostname... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Version - Sent as 1
TTL - value from 0000 to FFFF (see description below)
Sequence Number - A value to be used by clients in matching
requests to responses. For a periodic
(i.e. unsolicited) advertisement, should be 0. For
responses to explicit requests the value from the
request should be copied.
A TTL value of 0 indicates that the name/address pair is no longer
to be considered valid, and should be flushed from any long-term
storage on remote systems. A TTL value of 0xFFFF indicates an
infinite value, and clients are permitted to treat the
name/address pair as permanent, obviating the need to time out the
entry.
The Length field indicates the total length of the packet in
octets.
A system may transmit these packets solely at discrete intervals,
or only in response to specific requests. However, a mixture of
these two models (i.e. periodic advertisements, with direct
response to queries) would probably be the most reasonable
solution.
4.2 Client Processing and Requests
A system may operate in a purely reactionary mode to user
requests, with no caching of learned information, but it may well
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choose to record any advertised name/address bindings received.
If information is stored, then the values of the TTL field in
responses must be respected, and the associated information dealt
with accordingly. The following table shows possible TTL values,
and how they affect recording client systems.
TTL Value Action
1<n<FFFE Keep track of time
FFFF Permanent (no need to keep track of time)
0 Stale, flush existing entry.
The following items should be considered when verifying a received
advertisement.
- minimum packet length = 20. octets
- maximum packet length = maximum UDP limit on specific link
- Version value must be 1.
- non link-local address (wrong prefix or token length)
discarded
- zero length names discarded.
- Unrecognized packet types ignored/discarded
A system may also request a name or address value, via the
following request packet:
3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | R Q S T | T Y P E | L E N G T H |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S e q u e n c e N u m b e r | R e s e r v e d |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Simple hostname... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version - Send as 1.
RQST - Request Information (2.)
TYPE
Name (1.) Request a name for the given address.
Address (2.) Request an address for the given name.
If a Name is requested, then the address field must be set to a
valid link-local address for the given media type, and the
hostname field must be empty (i.e. of length zero). If an address
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is requested, then the address field must be set to all zeroes,
and the hostname field must contain a non-null entry. The Length
field indicates the total length of the packet in octets.
5. Interaction with DNS and resolver routines
To be useful and available to applications and users, the names
and addresses made available using this protocol must be
integrated to some extent with the host's name resolving software.
While it might be envisioned that this could be done in a
simplistic fashion, by adding and mainting entries in the local
storage (e.g. the "/etc/hosts" file), it would be more appropriate
to utilize dynamic storage for link local addresses. In fact, it
may well be useful to define a special category to this type of
address, given its restricted capabilities. A special pseudo-
domain, such as ".link", would be a very useful mechanism, both
for the unambiguous representation of these names, and as a system
configuration mechanism (e.g. the resolving software could be
configured to return address in the order BIND/LOCAL/LINK).
6. Alternative uses
Using this protocol for other purposes, such as a means of making
a host's neighbors visible to the host's users, as a simplistic
network management tool, is a possible extension of this
application. Such uses are not defined in this specification.
It is also unclear if link-local name servers should be permitted,
in which one system provides answers on behalf of another. This
would require some sort of "proxy bit" in the Advertisement
message.
7. Multilink issues
There are two sets of issues to consider, those of the multilink
server, and those of the client in a multilink environment.
For the multilink system to accurately provide name and addressing
information, it is merely necessary to restrict the advertisement
of addressing information for a particular address to the
interface to which the address is assigned.
Any client may have a multilink neighbor, and thus SHOULD be
prepared to deal with a single name being resolved to multiple
addresses. In practice, this could be handled in the same way as
any fully qualified hostname returning multiple addresses,
although returning the address with the largest TTL, or the first
received address, may be considered.
A client which is itself multilink may need to store the received
interface along with the name/address pair. Not enough is known
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of multilink behaviour to state this with certainty, however.
8. Security Issues
This proposal provides no additional mechanism for security, above
and beyond the ability to disable this particular function. It
might be extreme naivete on the part of the author, but he cannot
fathom any potential security risk in providing a simple name
associated with an easily obtainable address of limited scope.
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Acknowledgements
Thanks to the members of the Digital UNIX IPv6 team, and the
reviewers. Also, it has been brought to my attention that RFC 1788
[DOMAIN-MESSAGES], by William Simpson, uses similar techniques at a
different level (ICMP) to solve a problem of greater scope; although
it was not used in the initial design of this mechanism, it was very
useful during initial review of this draft. In particular, the
Sequence Number field was borrowed.
References
[ADDR-ARCH] R. Hinden and S. Deering, "Internet Protocol Version (IPv6)
Addressing Architecture", RFC1884.
[ADDRCONF] S. Thompson and T. Narten, "IPv6 Stateless Address
Autoconfiguration", work in progress, December 1995,
draft-ietf-addrconf-ipv6-auto-07.txt
[DNS-CONCEPTS] P. Mockapetris, "Domain names - concepts and facilities",
STD-13.
[MULTILINK] M. Shand and M. Thomas, "Multihoming Support in IPv6",
work in progress, February 1996,
draft-shand-ipv6-multi-homing-00.txt
[DOMAIN-MESSAGES] W. Simpson, "ICMP Domain Name Messages", RFC 1788.
Author's Address
Dan Harrington
Digital Equipment Corporation
550 King Street, LKG2-2/Q5
Littleton, MA 01460
Phone: (508) 486-7643
Email: dan@lkg.dec.com
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