IRTF HIP Research Group J. Ahrenholz
Internet-Draft The Boeing Company
Intended status: Informational September 9, 2009
Expires: March 13, 2010
HIP DHT Interface
draft-ahrenholz-hiprg-dht-05
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Abstract
This document specifies a common interface for using HIP with a
Distributed Hash Table service to provide an unmanaged name-to-HIT
lookup service and a HIT-to-address lookup service.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. The OpenDHT interface . . . . . . . . . . . . . . . . . . . . 5
3. HIP lookup services . . . . . . . . . . . . . . . . . . . . . 8
3.1. HIP name to HIT lookup . . . . . . . . . . . . . . . . . . 9
3.2. HIP address lookup . . . . . . . . . . . . . . . . . . . . 11
4. HDRR - the HIP DHT Resource Record . . . . . . . . . . . . . . 15
5. When to use the HIP lookup services . . . . . . . . . . . . . 17
6. Issues with DHT support . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 24
A.1. Changes from Version 04 to 05 . . . . . . . . . . . . . . 24
A.2. Changes from Version 03 to 04 . . . . . . . . . . . . . . 24
A.3. Changes from Version 02 to 03 . . . . . . . . . . . . . . 24
A.4. Changes from Version 01 to 02 . . . . . . . . . . . . . . 24
A.5. Changes from Version 00 to 01 . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The Host Identity Protocol [RFC5201] may benefit from a lookup
service based on Distributed Hash Tables (DHTs). The Host Identity
namespace is flat, consisting of public keys, in contrast to the
hierarchical Domain Name System. These keys are hashed and prefixed
to form Host Identity Tags (HITs) which appear as large random
numbers. The current DNS system does not provide a suitable lookup
mechanism for these flat, random values, and has been heavily
optimized for address lookup. DHTs manage such data well by applying
a hash function that distributes data across a number of servers.
DHTs also feature good support for frequently updating stored values.
One freely available implementation of a DHT is the Bamboo DHT, which
is Java-based software that has been deployed on PlanetLab servers to
form a free service named OpenDHT. OpenDHT was available via the
Internet for any program to store and retrieve arbitrary data.
OpenDHT used a well defined XML-RPC interface, featuring put, get,
and remove operations. OpenLookup is another deployment of open
source software compatible with this OpenDHT interface. This
document discusses a common way for HIP to use this OpenDHT
interface, so that various HIP experimenters may employ lookup
services in an interoperable fashion.
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2. The OpenDHT interface
OpenDHT was a public deployment of Bamboo DHT servers that ran on
about 150 PlanetLab nodes, retired in July 2009. While the Bamboo
project provides the actual software running on the servers, here we
will refer only to OpenDHT, which uses a certain defined interface
for the XML-RPC calls. Another service compatible with this
interface is OpenLookup. One can run their own Bamboo nodes to set
up a private ring of servers, but here we are interested in providing
a service for use with multiple, different HIP implementations.
OpenDHT was chosen because it was a well-known, publicly available
DHT used within the research community. Its interface features a
simple, standards-based protocol that can be easily implemented by
HIP developers. This document does not aim to dictate that only the
services and servers described here should be used, but is rather
meant to act as a starting point to gain experience with these
services, choosing tools that are readily available.
OpenDHT stores values using (hash) keys. Keys are limited to 20
bytes in length, and values can be up to 1024 bytes. Values are
stored for a certain number of seconds, up to a maximum of 604,800
seconds (one week.) See the OpenDHT website:
<http://www.opendht.org/>
Three RPC operations are supported: put, get, and rm (remove). Put
is called with key and value parameters, causing the value to be
stored using the key as its hash index. Get is called with the key
parameter, when you have a key and want to retrieve the value. Rm is
called with a hash of the value to be removed along with a secret
value, a hash of which was included in the put operation.
The definitions below are taken from
<http://opendht.org/users-guide.html>.
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The put operation takes the following arguments:
+----------------+--------------------------------------+
| field | type |
+----------------+--------------------------------------+
| application | string |
| | |
| client_library | string |
| | |
| key | byte array, 20 bytes max. |
| | |
| value | byte array, 1024 bytes max. |
| | |
| ttl_sec | four-byte integer, max. value 604800 |
| | |
| secret_hash | optional SHA-1 hash of secret value |
+----------------+--------------------------------------+
The server replies with an integer -- 0 for "success", 1 if it is
"over capacity", and 2 indicating "try again".
The get operation takes the following arguments:
+----------------+---------------------------------------------+
| field | type |
+----------------+---------------------------------------------+
| application | string |
| | |
| client_library | string |
| | |
| key | byte array, 20 bytes max. |
| | |
| maxvals | four-byte singed integer, max. value 2^31-1 |
| | |
| placemark | byte array, 100 bytes max. |
+----------------+---------------------------------------------+
The server replies with an array of values, and a placemark that can
be used for fetching additional values.
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The rm operation takes the following arguments:
+----------------+----------------------------------------------+
| field | type |
+----------------+----------------------------------------------+
| application | string |
| | |
| client_library | string |
| | |
| key | byte array, 20 bytes max. |
| | |
| value_hash | SHA-1 hash of value to remove |
| | |
| ttl_sec | four-byte integer, max. value 604800 |
| | |
| secret | secret value (SHA-1 of this was used in put) |
+----------------+----------------------------------------------+
The server replies with an integer -- 0 for "success", 1 if it is
"over capacity", and 2 indicating "try again".
This is the basic XML-RPC interface provided by OpenDHT. Each
"field" from the above tables are XML tags that enclose their
corresponding values. Below, specific uses for HIP are suggested,
along with values that can be used inside the fields shown above.
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3. HIP lookup services
This draft defines a HIT lookup and address lookup service for use
with HIP. The HIT lookup uses a text name to discover a peer's HIT.
The address lookup uses a peer's HIT to discover its current
addresses.
HIT = get(SHA1("name"))
HDRR = get(HIT_KEY)
The HIT lookup service returns the Host Identity Tag of a peer given
a name. The name could be the FQDN, hostname, or other alias. The
HIT is the hash of the public-key based Host Identity as described in
[RFC5201]. There are no security properties of the name, unlike the
HIT. This service can be used when legacy DNS servers do not support
HIP resource records, or when hosts do not have administrative access
to publish their own DNS records. Such an unmanaged naming service
may help facilitate experimentation.
The address lookup uses a HIP DHT Resource Record (HDRR) described in
Section 4. Before a HIP association can be initiated (a non-
opportunistic initiation), a HIP host needs to know the peer's HIT
and the current address at which the peer is reachable. Often the
HIT will be pre-configured, available via DNS lookup using a hostname
lookup [RFC5205], or retrieved using the HIT lookup service defined
in this document. With HIP mobility [RFC5206], IP addresses may be
used as locators that are often subject to change. The Host Identity
and the HIT remain relatively constant and can be used to securely
identify a host, so the HIT serves as a suitable DHT key for storing
and retrieving addresses.
The address lookup service includes the peer's Host Identity and a
signature over the locators. This allows the DHT client or server to
validate the address information stored in the DHT.
These two separate lookups are defined instead of one because the
address record is expected to change more frequently, while the name-
to-HIT binding should remain relatively constant.
These services reduce the amount of pre-configuration required at
each HIP host. The address of each peer no longer needs to be known
ahead of time, if peers also participate by publishing their
addresses. If peers choose to publish their HITs with a name, peer
HITs also no longer need pre-configuration. However, discovering an
available DHT server for servicing these lookups will require some
additional configuration.
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3.1. HIP name to HIT lookup
Given the SHA-1 hash of a name, a lookup returns the HIT of the peer.
The hash of a name is used because OpenDHT keys are limited to 20
bytes, so this allows for longer names. Publish, lookup, and remove
operations are defined.
HIT = get(SHA-1("name"))
put(SHA-1("name", HIT, [secret])
rm(SHA-1("name", HIT, secret)
HIT publish
+----------------+----------------------------------+---------------+
| field | value | data type |
+----------------+----------------------------------+---------------+
| application | "hip-name-hit" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | SHA-1 hash of name | base64 |
| | | encoded |
| | | |
| value | 128-bit HIT | base64 |
| | | encoded |
| | | |
| ttl_sec | name lifetime | numeric |
| | | string |
| | | |
| secret_hash | optional SHA-1 hash of secret | base64 |
| | value | encoded |
+----------------+----------------------------------+---------------+
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HIT lookup
+----------------+---------------------------------+----------------+
| field | value | data type |
+----------------+---------------------------------+----------------+
| application | "hip-name-hit" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | SHA-1 hash of name | base64 encoded |
| | | |
| maxvals | (implementation dependent) | numeric string |
| | | |
| placemark | (NULL, or used from server | base64 encoded |
| | reply) | |
+----------------+---------------------------------+----------------+
HIT remove (optional)
+----------------+------------------------------------+-------------+
| field | value | data type |
+----------------+------------------------------------+-------------+
| application | "hip-name-hit" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | SHA-1 hash of name | base64 |
| | | encoded |
| | | |
| value_hash | SHA-1 hash of address value to | base64 |
| | remove | encoded |
| | | |
| ttl_sec | name lifetime | numeric |
| | | string |
| | | |
| secret | secret value (SHA-1 of this was | base64 |
| | used in put) | encoded |
+----------------+------------------------------------+-------------+
The key for both HIT publish and lookup is the SHA-1 hash of the
name. The name does not necessarily need to be associated with a
valid DNS or host name. It does not need to be related to the Domain
Identifier found in HI TLV. OpenDHT limits the keys to 20 bytes in
length, so the SHA-1 hash is used to allow arbitrary name lengths.
The value used in the publish and lookup response is the base64-
encoded 128-bit HIT. This value is the full 128 binary bits of the
HIT, which can be identified as a HIT both by its length and by the
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ORCHID prefix ([RFC4843]) that it starts with.
The ttl_sec field specifies the number of seconds requested by the
client that the entry should be stored by the DHT server, which is
implementation dependent. Note that this value may not be honored by
the server.
The secret_hash is an optional field used with HIT publish if the
value will later be removed with an rm operation. The secret_hash
contains the base64 encoded SHA-1 hash of some secret value known
only to the publishing host. The max_vals and placemark fields used
with the HIT lookup are defined by the get XML-RPC interface.
3.2. HIP address lookup
Given a HIT, a lookup returns the HIP DHT Resource Record (HDRR) for
the peer. This interface has publish, lookup, and remove operations.
HDRR = get(HIT_KEY)
put(HIT_KEY, HDRR, [secret])
rm(HIT_KEY, HDRR, secret)
The HDRR is defined in Section 4. It contains one or more locators
that the peer wants to publish, and the peer's Host Identity and
signature over the contents.
The HIT_KEY is a portion of the HIT used as a DHT key. [RFC4843]
defines the HIT as a Prefix concatenated with 100 bits of hash:
Input := any bitstring
Hash Input := Context ID | Input
Hash := Hash_function( Hash Input )
ORCHID := Prefix | Encode_100( Hash )
The HIT_KEY is the Encode_100( Hash ) portion of the above
definition. Zero padding is appended to this 100-bit value to fill
the length required by the DHT, 160 bits total. The HIT's ORCHID
Prefix is dropped because this would cause uneven distribution of the
stored values across the DHT servers.
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Address publish
+----------------+----------------------------------------+---------+
| field | value | data |
| | | type |
+----------------+----------------------------------------+---------+
| application | "hip-addr" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | 100-bit HIT_KEY | base64 |
| | | encoded |
| | | |
| value | HDRR | base64 |
| | | encoded |
| | | |
| ttl_sec | amount of time HDRR should be valid, | numeric |
| | or the lifetime of the preferred | string |
| | address | |
| | | |
| secret_hash | optional SHA-1 hash of secret value | base64 |
| | | encoded |
+----------------+----------------------------------------+---------+
Address lookup
+----------------+---------------------------------+----------------+
| field | value | data type |
+----------------+---------------------------------+----------------+
| application | "hip-addr" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | 100-bit HIT_KEY | base64 encoded |
| | | |
| maxvals | (implementation dependent) | numeric string |
| | | |
| placemark | (NULL, or used from server | base64 encoded |
| | reply) | |
+----------------+---------------------------------+----------------+
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Address remove (optional)
+----------------+-------------------------------------+------------+
| field | value | data type |
+----------------+-------------------------------------+------------+
| application | "hip-addr" | string |
| | | |
| client_library | (implementation dependent) | string |
| | | |
| key | 100-bit HIT_KEY | base64 |
| | | encoded |
| | | |
| value_hash | SHA-1 hash of HDRR (value used | base64 |
| | during publish) to remove | encoded |
| | | |
| ttl_sec | old address lifetime | numeric |
| | | string |
| | | |
| secret | secret value (SHA-1 of this was | base64 |
| | used in put) | encoded |
+----------------+-------------------------------------+------------+
The application and client_library fields are used for logging in
OpenDHT. The client_library may vary between different
implementations, specifying the name of the XML-RPC library used or
the application that directly makes XML-RPC calls.
The key for both address publish and lookup is the 100-bits of the
HIT_KEY as defined above, plus 60-bits of zero padding, base64
encoded [RFC2045]. The value used in the publish and lookup response
is the base64 encoded HDRR containing one or more LOCATORs.
The ttl_sec field used with address publish includes the time-to-
live, the number of seconds for which the entry will be stored by the
DHT, which is set to the number of seconds remaining in the address
lifetime.
The secret_hash is an optional field used with address publish, used
if the value will later be removed with an rm operation. The
secret_hash contains the base64 encoded SHA-1 hash of some secret
value known only to the publishing host. Clients SHOULD include the
secret_hash and remove outdated values to reduce the amount of data
the peer needs to handle.
The max_vals and placemark fields used with address lookup are
defined by the get XML-RPC interface. The get operation needs to
know the maximum number of values to retrieve. The placemark is a
value found in the server reply that causes the get to continue to
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retrieve values starting at where it left off.
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4. HDRR - the HIP DHT Resource Record
The HIP DHT Resource Record uses the same binary format as HIP
packets (defined in [RFC5201].) This packet encoding is used as a
convenience, even though this data is actually a resource record
stored and retrieved by the DHT servers, not a packet sent on the
wire by a HIP protocol daemon. Note that this HDRR format is
different than the HIP RR used by the Domain Name System as defined
in [RFC5205].
HIP header values for the HDRR:
HIP Header:
Packet Type = 20 (this value is TBD)
SRC HIT = Sender's HIT
DST HIT = NULL
HIP ( LOCATOR, HOST_ID, HIP_SIGNATURE )
The Initiator HIT (Sender's HIT, SRC HIT) is set to the HIT that the
host wishes to make available using the lookup service. This HIT is
the same one used to derive the HIT_KEY used as the DHT key. The
Responder HIT (Receiver's HIT, DST HIT) MUST be NULL (all zeroes)
since the data is intended for any host.
The LOCATOR parameter contains the addresses that the host wishes to
make available using the lookup service. A host may publish its
current preferred IPv4 and IPv6 locators, for example.
The HOST_ID parameter contains the Host Identity that corresponds
with the Sender's HIT. (The encoding of this parameter is defined in
section 5.2.8 of [RFC5201].)
The HOST_ID parameter and HIP_SIGNATURE parameter MUST be used with
the HDRR so that HIP clients receiving the record can validate the
sender and the included LOCATOR parameter. The HIT_KEY used for the
DHT key will also be verified against the Host Identity.
The client that receives the HDRR from the DHT response MUST perform
the signature and HIT_KEY verification. If the signature is invalid
for the given Host Identity or the HIT_KEY used to retrieve the
record does not match the Host Identity, the DHT record retrieved
MUST be ignored. Note that for client-only verification the DHT
server does not need to be modified, so this would work on the
existing OpenDHT PlanetLab deployment.
The DHT server could also verify the SIGNATURE and HOST_ID. This
document primarily describes using the legacy OpenDHT service. Such
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Host Identity and signature verification would require modifications
to the DHT server software. Users running their own server can run
the Bamboo DHT software, on which OpenDHT is based, with some
modifications. The signature in the put needs to be verified using
the given Host Identity, and the HIT_KEY provided as the key needs to
match this Host Identity. If either signature or HIT verification
fails, the put is not recorded into the DHT. Full specification of
this HIP-aware server behavior is outside the scope of this draft.
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5. When to use the HIP lookup services
Below are some suggestions of when a HIP implementation may want to
use the HIT and address lookup services.
To learn of a peer's HIT, a host might first consult DNS using the
peer's hostname if the DNS server supports the HIP Resource Record
defined by [RFC5205]. Sometimes hosts do not have administrative
authority over their DNS entries and/or the DNS server is not able to
support HIP resource records. Hosts may want to associate other non-
DNS names with their HITs. For these and other reasons, a host may
use the HIT publish service defined in Section 3.1. The peer HIT may
be learned by performing a DHT lookup of such a name.
Once a peer HIT is learned or configured, an address lookup could be
performed so that the LOCATORs can be cached and immediately
available for when an association is requested. Implementations
might load a list of peer HITs on startup, resulting in several
lookups that can take some time to complete.
However, cached LOCATORs may quickly become obsolete, depending on
how often the peer changes its preferred address. Performing an
address lookup before sending the I1 may be needed. At this time the
latency of a lookup may be intolerable, and a lookup could instead be
performed after the I1 retransmission timer fires -- when no R1 reply
has been received -- to detect any change in address.
A HIP host should publish its preferred LOCATORs upon startup, so
other hosts may determine where it is reachable. The host needs to
periodically refresh its HDRR entry because each entry carries a TTL
and will eventually expire. Also, when there is a change in
preferred address, usually associated with sending UPDATE packets
with included locator parameters, the host should update its HDRR
with the DHT. The old HDRR should be removed using the rm operation,
if a secret value was used in the put.
Addresses from the private address space should not be published to
the DHT. If the host is located behind a NAT, for example, the host
could publish the address of its RVS to the DHT if that is how it is
reachable. In this case however, a peer could instead simply use the
RVS field of the NATted host's HIP DNS record, which would eliminate
a separate DHT lookup.
A HIP host should also publish its HIT upon startup or whenever a new
HIT is configured, for use with the HIT lookup service, if desired.
The host should first check if the name already exists in the DHT by
performing a lookup, to avoid interfering with an existing name-to-
HIT mapping. The name-to-HIT binding needs to be refreshed
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periodically before the TTL expires. A host may want to update its
published values periodically, per local policy, more frequently then
the specified TTL.
When publishing data to the DHT server, care should be taken to check
the response from the server. The server may respond with an "over
capacity" code, indicating that its resources are too burdened to
honor the given size and TTL. The host should then select another
server for publishing, or reduce the TTL and retry the put operation.
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6. Issues with DHT support
Each put operation appends the new value to any existing values. If
a host does not remove its old HDRR before adding another, several
entries may be present. Therefore when performing an address lookup,
the last HDRR in the DHT response list should be used and considered
to contain the current preferred address. Before performing each put
a host should remove its old HDRR data using the rm operation.
In the case of the HIT lookup service, there is nothing preventing
different hosts from publishing the same name. A lookup performed on
this name will return multiple HITs that belong to different devices.
This is an unmanaged free-for-all service, so this issue will not be
solved here; it is recommended that a host simply pick another name.
Selecting an appropriate DHT server to use is not covered here. If a
particular server becomes unavailable, the connect will timeout and
some server selection algorithm should be performed, such as trying
the next server in a configured list. OpenDHT formerly provided a
DNS-based anycast service, when you performed a lookup of
"opendht.nyuld.net", it returned the two nearest OpenDHT servers.
Because the put and get calls rely on outside servers located across
the Internet, operations may have a latency involved that should be
considered when using these services with HIP.
The maximum size of 1024 bytes for the value field will limit the
maximum size of the Host Identity that may be used within the HDRR.
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7. Security Considerations
There are two classes of attacks on this information exchange between
host and DHT server: attacks on the validity of the information
provided by the DHT to the host (such as a spoofed DHT response) and
attacks on the DHT records themselves (such as polluted records for a
given key). Without an authenticated and trusted service, not much
can be done to prevent these attacks.
For the HIT lookup based on name (Section 3.1), there are no
guarantees on the validity of the HIT. Users concerned with the
validity of HITs found in the DHT should simply exchange HITs out-of-
band with peers. Including a signature will not help here because
the HIT that identifies the Host Identity for signing is not known
ahead of time.
For the address lookup based on HIT (Section 3.2), the validity of
the DHT response can be checked with the HOST_ID and SIGNATURE
parameters in the HDRR. A HIP initiating host can also validate the
DHT response after the R1 message is received during a HIP exchange.
The Host Identity provided in the R1 can be hashed to obtain a HIT
that can be checked against the original HIT. However, the legacy
OpenDHT service does not currently prevent an attacker from polluting
the DHT records for a known HIT, thereby causing a denial-of-service
attack, since server validation is not performed.
Relying solely on client validation may be harmful. An attacker can
replay the put packets containing the signed HDRR, possibly causing
stale or invalid information to exist in the DHT. If an attacker
replays the signed put message and changes some aspect each time, and
if the server is not performing signature and HIT validation, there
could be a multitude of invalid entries stored in the DHT. When a
client retrieves these records it would need to perform signature and
HIT verification on each one, which could cause unacceptable amounts
of delay or computation.
To protect against this type of attack, the DHT server could be
running HIP and requiring client authentication with a HIP
association before accepting HDRR puts. Also a HIP-aware DHT server
could be developed to perform the HIT and signature verification of
each put. This is briefly described in Section 4.
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8. IANA Considerations
This document has no actions for IANA.
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9. Acknowledgments
Thanks to Tom Henderson, Samu Varjonen, Andrei Gurtov, Miika Komu,
and Kristian Slavov for providing comments. Samu most notably
contributed the resolver packet and its suggested parameters, which
became the HDRR here.
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10. References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC4843] Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
for Overlay Routable Cryptographic Hash Identifiers
(ORCHID)", RFC 4843, April 2007.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
"Host Identity Protocol", RFC 5201, April 2008.
[RFC5205] Nikander, P. and J. Laganier, "Host Identity Protocol
(HIP) Domain Name System (DNS) Extensions", RFC 5205,
April 2008.
[RFC5206] Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "End-
Host Mobility and Multihoming with the Host Identity
Protocol", RFC 5206, April 2008.
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Appendix A. Change Log
A.1. Changes from Version 04 to 05
Reordered Sections 3.2 and 3.1, since the HIT lookup normally occurs
before the address lookup. Added text about why two separate lookups
are defined. Added text pertaining to the OpenDHT service retiring.
A.2. Changes from Version 03 to 04
Revised text about server treatment of TTL.
A.3. Changes from Version 02 to 03
Added text about TTL expiration, appending zero padding, HIT value
usage. Removed text on anonymous bit. Use RFC references.
A.4. Changes from Version 01 to 02
sockaddr address format changed to use HIP DHT Resource Record
containing the HIP LOCATOR format. The HIT prefix is dropped before
using it as a key. Separate "secure" service was dropped, and
signatures made mandatory. Legacy versus hip-aware DHT servers are
distinguished. Text packet examples added.
A.5. Changes from Version 00 to 01
Removed the HIT lookup service -- using the LSI as a key to return a
HIT as the value -- and added a HIT lookup service using names.
Added support for OpenDHT remove. Changed all occurrences of "Open
DHT" to "OpenDHT".
Added the Host Identity and a signature as a secure address lookup
service, with text about running a modified OpenDHT server that can
verify signed put messages based on Host Identity signatures.
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Author's Address
Jeff Ahrenholz
The Boeing Company
P.O. Box 3707
Seattle, WA
USA
Email: jeffrey.m.ahrenholz@boeing.com
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