Internet DRAFT - draft-doi-ipv6-anycast-func-term
draft-doi-ipv6-anycast-func-term
Individual Submission M. Hashimoto
Internet-Draft Osaka University
Expires: July 20, 2006 S. Ata
Osaka City University
H. Kitamura
NEC Corporation
M. Murata
Osaka University
January 19, 2006
IPv6 Anycast Terminology Definition
draft-doi-ipv6-anycast-func-term-05
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The purpose of this document is to clarify the usage of terms for
IPv6 Anycast and help increase its popularity. This document
discusses not only Anycasting's terminology but also its
categorization and clarifies its outline. In this document, we focus
on network-layer Anycast, which is defined in IPv6 specifications.
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1. Introduction
In IPv6 networks, a service-oriented address can be assigned to an
interface called Anycast that identifies a set of interfaces. A
packet sent to an Anycast address is delivered to one of the
interfaces assigned that address. This interface is the optimum one
according to some anycast routing mechanisms.
Since many people are interested in Anycast, it is necessary to
define Anycast related terms to use them in common. This document
will clarify the usage of terms for IPv6 Anycast and support
documents about IPv6 Anycast. We focus on network-layer Anycast,
which is defined in IPv6 specifications [ADDR-ARCH].
2. Definition Format
Definitions in this document accompany the following format.
o Term to be defined.
Definition:
The specific definition of the term.
Discussion:
A brief discussion of the term, its application and other
information that builds understanding.
[See Also:]
A list of other terms relevant to discussion of this term. This
field is optional in this document.
3. Basic Terms
We first define basic terms which are generally used in Anycast
related documents. Fig. 1 shows the basic model of Anycasting.
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Anycast Responder
+-----+
| AR1 | (Anycast Address: AA)
+-----+ (Peer Unicast Address: PUA1)
Anycast
Initiator Correspondent Anycast Responder
+----+ +-----------+
| AI |--------------------->| AR2 = CAR | (Anycast Address: AA)
+----+ Anycast +-----------+ (Peer Unicast Address: PUA2
Communication = Correspondent PUA: CPUA)
Anycast Responder
+-----+
| AR3 | (Anycast Address: AA)
+-----+ (PUA: PUA3)
Fig. 1 Basic Model of Anycasting
3.1 Addresses
o Anycast Address (AA)
Definition:
An address used for Anycast Communication has already defined in
[ANYCASTING].
Discussion:
This address is a service-oriented address assigned to some
interfaces. Nodes to which the same Anycast Address is assigned
provide the same service. A packet sent to an Anycast address is
delivered to one of the interfaces which that address is assigned
to.
SeeAlso:
- Peer Unicast Address
- Anycast Prefix
o Anycast Prefix (AP)
Definition:
The prefix part of an Anycast Address.
Discussion:
Anycast Address is taken from unicast address spaces [ADDR-ARCH].
An assign method of Anycast Address is different from that of
unicast address. Anycast Address is not determined by node
location. We need to consider what kind of addresses should be
assigned as the Anycast Address. The assignment of Anycast
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Address depends on Anycast types (see Section 4). In Global
Anycast, a prefix of the Anycast Address equals to the Anycast
Prefix.
SeeAlso:
- Subnet Anycast
- Global Anycast
- Anycast Routing
o Peer Unicast Address (PUA)
Definition:
A unicast address(es) assigned to the interface to which Anycast
Address is assigned.
Discussion:
An Anycast Address can be resolved to a Peer Unicast Address by
Anycast Address Resolving.
SeeAlso:
- Anycast Address
- Correspondent Peer Unicast Address
- Anycast Address Resolving
o Correspondent Peer Unicast Address (CPUA)
Definition:
A Peer Unicast Address assigned to the Correspondent Anycast
Responder.
Discussion:
SeeAlso:
- Anycast Address
- Peer Unicast Address
- Anycast Address Resolving
3.2 Packet
o Anycast Packet
Definition:
A packet whose destination address field is filled with an
Anycast Address.
Discussion:
An Anycast Packet is used for Anycast Communication. When there
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are plural Anycast Responders, one of the Anycast Responders is
selected to receive an Anycast Packet.
3.3 Node
o Anycast Initiator (AI)
Definition:
A node that sends an Anycast Packet and initiates Anycast
Communication.
Discussion:
Any node can become an Anycast Initiator. A node that wants a
particular service sends an Anycast Packet and becomes an Anycast
Initiator. We prefer to use "Initiator" instead of "Client"
because it is not appropriate to call Anycast Communication
client-server type communication. Anycast is basically used for
a one-shot type communication.
SeeAlso:
- Anycast Communication
- Anycast Responder
- Correspondent Anycast Responder
o Anycast Responder(s) (AR)
Definition:
A node that can respond to an Anycast packet.
Discussion:
Anycast Responder has an interface(s) assigned to an Anycast
Address. Only one Anycast Responder (Correspondent Anycast
Responder) receives an Anycast Packet sent from an Anycast
Initiator.
SeeAlso:
- Anycast Initiator
- Correspondent Anycast Responder
- Anycast Group Membership
o Correspondent Anycast Responder (CAR)
Definition:
A node that actually receives an Anycast Packet issued from an
Anycast Initiator.
Discussion:
When an Anycast Initiator sends an Anycast Packet, one of the
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nodes in the Anycast Group Membership is selected based on the
Anycast Responder Selection Criteria. The selected node is
called the Correspondent Anycast Responder. Even when using the
same Anycast Responder Selection Criteria, the Correspondent
Anycast Responder can be changed by Anycast Initiators'
locations, network conditions, etc.
SeeAlso:
- Anycast Responder Selection
- Anycast Group Membership
- Anycast Communication
- Anycast Responder
- Anycast Initiator
o Home Anycast Responder (HAR)
Definition:
An Anycast Responder that can receive Anycast Packets even by
unicast routing.
Discussion:
A Home Anycast Responder is a special Anycast Responder. Home
Anycast Responder's Peer Unicast Address equals its Anycast
Address.
SeeAlso:
- Anycast Responder
- Home Anycast Responder Link
- Peer Unicast Address
- Anycast Routing
o Anycast Router
Definition:
A router node that can deal with Anycast Routing Protocols.
Discussion:
SeeAlso:
- Anycast Routing
- Anycast Routing Table
- Anycast Routing Protocol
- Anycast Communication Path
3.4 Link
o Anycast Responder Link(s) (ARL)
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Definition:
The links to which one or more Anycast Responders belong.
Discussion:
SeeAlso:
- Anycast Responder
- Home Anycast Responder Link
o Home Anycast Responder Link (HARL)
Definition:
A link to which a Home Anycast Responder belongs.
Discussion:
SeeAlso:
- Home Anycast Responder
- Anycast Responder Link
o Anycast Initiator Link(s) (AIL)
Definition:
The links to which an Anycast Initiator belongs.
Discussion:
SeeAlso:
- Anycast Responder
- Home Anycast Responder Link
3.5 Communication
o Anycast Communication
Definition:
Communication initiated by an Anycast Initiator using an Anycast
Packet.
Discussion:
Anycast Communication is one-way communication from an Anycast
Initiator to a Correspondent Anycast Responder.
SeeAlso:
- Global Anycast
- Anycast Routing
- Anycast Communication Path
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o Anycast Communication Path (ACP)
Definition:
A path where an Anycast packet passes in Anycast communication.
Discussion:
SeeAlso:
- Global Anycast
- Anycast Routing
- Anycast Communication
4. Categorization of Anycast
Anycast is roughly classified into two types (Subnet Anycast and
Global Anycast) according to locations where Anycast Responders
exist.
o Subnet Anycast (SA)
Definition:
An Anycast which use an address whose lower bits are defined by
Anycast intrinsically.
| n bits | 128-n bits |
+----------------------------------------+------------------------+
| subnet prefix (= segments' prefix) | anycast intrinsic part |
+----------------------------------------+------------------------+
Fig. 2 Anycast Address for Subnet Anycast
Discussion:
An Anycast Address which is used in Subnet Anycast is based on
the Anycast Responder's unicast address prefix. In typical case,
all Anycast Responders are located on the same segment. Routers
forward this type of packets only by unicast routing information.
Some special routing mechanisms are not required. Because a
prefix of the address is depend on unicast address. In Subnet
Anycast, Anycast Packets can reach the last hop router by unicast
routing. When the last hop router receives the Anycast Packets,
the Anycast Responder is determined by the Neighbor Cache [ND] of
the last hop router. (i.e., Anycast Responder Selection is up to
the last hop router.) Fig. 2 shows Anycast Address format for
Subnet Anycast and Fig. 3 shows Subnet Anycast.
SeeAlso:
- Anycast Responder Selection
- Anycast Prefix
- Anycast Routing
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- Global Anycast
+----------+ | Anycast Responders
| | | +-----+
| | Router +----| AR1 |
Anycast | | +-----+ | +-----+
Initiator | |------| R |----+
+----+ | | +-----+ | +-----+
| AI |------| Internet | +----| AR2 |
+----+ | | | +-----+
| | |
| | | +-----+
| | +----| AR3 |
| | | +-----+
+----------+ |
Fig. 3 Subnet Anycast
o Global Anycast (GA)
Definition:
An Anycast which use an address whose whole bits are defined by
Anycast.
| 128 bits |
+-----------------------------------------------------------------+
| Anycast Address |
+-----------------------------------------------------------------+
Fig. 4 Anycast Address for Global Anycast
Discussion:
Unicast routing is useless for this type of addresses. Because
unicast address is not used for this address at all. Some
special Anycast Routing mechanisms are necessary to achieve
Global Anycast communications. Fig. 4 shows Anycast Address
format for Global Anycast and Fig. 5 shows Global Anycast.
In special cases, Subnet Anycast and Global Anycast are combined.
In such cases, an Anycast Packet is delivered to the last hop
router by Anycast Routing, which then delivers the Anycast Packet
according to its Neighbor Cache. An Anycast in this case is
shown in Fig. 6.
SeeAlso:
- Anycast Responder Selection
- Anycast Prefix
- Anycast Routing
- Anycast Communication Path
- Subnet Anycast
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Anycast Responders
+----------+ | +-----+
| | Routers +----| AR1 |
| | +-----+ | +-----+
| |------| R |----+
| | +-----+ |
| |
Anycast | |
Initiator | | +-----+ |
+----+ | |---------| R |----+
| AI |------| Internet | +-----+ | +-----+
+----+ | | +----| AR2 |
| | | +-----+
| |
| |
| | +-----+ |
| |------| R |----+
| | +-----+ | +-----+
| | +----| AR3 |
+----------+ | +-----+
Fig. 5 Global Anycast
+----------+ Anycast Responders
| | | +-----+
| | Routers +----| AR1 |
| | +-----+ | +-----+
Anycast | |------| R |----+
Initiator | | +-----+ | +-----+
+----+ | | +----| AR2 |
| AI |------| Internet | | +-----+
+----+ | |
| |
| | +-----+ |
| |---------| R |----+
| | +-----+ | +-----+
| | +----| AR3 |
+----------+ | +-----+
Fig. 6 Global Anycast plus Subnet Anycast
5. Anycast Routing
This section defines terms related to Anycast Routing.
o Anycast Routing
Definition:
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Routing for Anycast Communication.
Discussion:
An Anycast Packet is delivered from an Anycast Initiator to an
Anycast Responder via Anycast Routing.
SeeAlso:
- Anycast Router
- Anycast Routing Table
- Anycast Routing Protocol
o Anycast Routing Table
Definition:
A routing table for Anycast Routing.
Discussion:
All Anycast Routers have Anycast Routing Tables. An Anycast
Initiator may also have an Anycast Routing Table.
SeeAlso:
- Anycast Routing
- Anycast Router
- Anycast Routing Protocol
- Peer Unicast Address
- Anycast Address Resolving
o Anycast Routing Protocol
Definition:
A routing protocol for anycasting.
Discussion:
SeeAlso:
- Anycast Routing
- Anycast Router
- Anycast Routing Table
o Anycast Address Resolving (AAR)
Definition:
To resolve an Anycast Address to the Peer Unicast Address.
Discussion:
By considering Anycast a service discovery mechanism [AARP],
after an Anycast Responder is discovered, the Anycast Initiator
uses the server's Peer Unicast Address for continuous
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communication.
SeeAlso:
- Anycast Address
- Peer Unicast Address
6. Anycast Responder Selection
o Anycast Responder Selection (ARS)
Definition:
The selection of a Correspondent Anycast Responder from an
Anycast Group Membership.
Discussion:
SeeAlso:
- Anycast Responder Selection Criteria
- Anycast Group Membership
- Correspondent Anycast Responder
- Candidate(s) for Correspondent Anycast Responder
o Anycast Responder Selection Criteria (ARSC)
Definition:
The selection criteria of a Correspondent Anycast Responder from
Anycast Group Membership.
Discussion:
SeeAlso:
- Anycast Responder Selection
- Anycast Group Membership
- Correspondent Anycast Responder
- Candidate(s) for Correspondent Anycast Responder
o Anycast Group Membership (AGM)
Definition:
A set of nodes that have interfaces with the same Anycast
Address.
Discussion:
A node can join the Anycast Group Membership to become an Anycast
Responder, and an Anycast Responder can quit the Anycast Group
Membership.
SeeAlso:
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- Anycast Responder
- Anycast Responder Selection
o Anycast Initiator's Scope (AIS)
Definition:
A zone where an Anycast Packet, which one Anycast Initiator
sends, can reach.
Discussion:
In other words, a zone Candidate(s) for Correspondent Anycast
Responder exist(s).
SeeAlso:
- Candidates for Correspondent Anycast Responder
- Anycast Responder's Service Zone
- Anycast Group Membership
o Anycast Responder's Service Zone (ARSZ)
Definition:
A zone where an Anycast Responder can respond to an Anycast
Packet issued by an Anycast Initiator.
Discussion:
SeeAlso:
- Candidates for Correspondent Anycast Responder
- Anycast Initiator's Scope
- Anycast Group Membership
o Candidates for Correspondent Anycast Responder (CCAR)
Definition:
Anycast Responder(s) that can receive an Anycast Packet from one
Anycast Initiator.
Discussion:
SeeAlso:
- Anycast Responder
- Anycast Group Membership
- Anycast Initiator's Scope
- Anycast Responder's Service Zone
7. Security Considerations
This paper does not address any Anycast security issues.
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Anycast security descriptions are shown in [ANALYSIS].
8. References
[ANYCASTING] Partridge, C., and Mendez, T., and Milliken, T.,
"Host Anycasting Service," RFC1546, November 1993
[ADDR-ARCH] Hinden, R., and Deering, S., "IP Version 6 Addressing
Architecture," RFC3513, April 2003.
[ANALYSIS] Hagino, J., and Ettikan, K., "An Analysis of IPv6
Anycast," <draft-ietf-ipngwg-ipv6-anycast-analysis-02.txt>,
June 2003 "work in progress."
[SUBNET] Johnson, D., and Deering, S., "Researved IPv6 Subnet
Anycast Addresses," RFC2526, March 1999.
[ADDR-AUTO] Thomson, S., Narten, T., "IPv6 Stateless Address
Autoconfiguration," RFC2462, December 1998.
[ND] Narten, T., Nordmark, E., and Simpson, W., "Neighbor
Discovery for IP Version 6 (IPv6)," RFC 2461,
December 1998.
[AARP] Ata, S., Kitamura, H., and Murata, M., "A Protocol
for Anycast Address Resolving,"
<draft-ata-ipv6-anycast-resolving-00.txt>,
June 2002.
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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9. Authors' Addresses
Masakazu Hashimoto
Osaka University
1-5 Yamadaoka, Suita-shi
Osaka 565-0871
Japan
Phone: +81-6-6879-4542
Fax: +81-6-6879-4544
Email: msk-hasi@ist.osaka-u.ac.jp
Shingo Ata
Osaka City University
3-3-138, Sugimoto, Sumiyoshi-ku
Osaka 558-8585
Japan
Phone: +81-6-6605-2191
Fax: +81-6-6690-5382
EMail: ata@info.eng.osaka-cu.ac.jp
Hiroshi Kitamura
NEC Corporation
(Igarashi Building 4F) 11-5, Shibaura 2-Chome
Minato-ku, Tokyo 108-8557
Japan
Phone: +81-3-5476-1071
Fax: +81-3-5476-1005
EMail: kitamura@da.jp.nec.com
Masayuki Murata
Osaka University
1-5 Yamadaoka, Suita-shi
Osaka 565-0871
Japan
Phone: +81-6-6879-4543
Fax: +81-6-6879-4544
EMail: murata@ist.osaka-u.ac.jp
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