Network Working Group M. Daniele
Request for Comments: 4001 SyAM Software, Inc.
Obsoletes: 3291 B. Haberman
Category: Standards Track Johns Hopkins University
 S. Routhier
 Wind River Systems, Inc.
 J. Schoenwaelder
 International University Bremen
 February 2005
 Textual Conventions for Internet Network 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 MIB module defines textual conventions to represent commonly
 used Internet network layer addressing information. The intent is
 that these textual conventions will be imported and used in MIB
 modules that would otherwise define their own representations.
Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2. The Internet-Standard Management Framework . . . . . . . . . . 4
 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
 4. Usage Hints . . . . . . . . . . . . . . . . . . . . . . . . . 13
 4.1. Table Indexing . . . . . . . . . . . . . . . . . . . . . 14
 4.2. Uniqueness of Addresses . . . . . . . . . . . . . . . . 14
 4.3. Multiple Addresses per Host . . . . . . . . . . . . . . 15
 4.4. Resolving DNS Names . . . . . . . . . . . . . . . . . . 15
 5. Table Indexing Example . . . . . . . . . . . . . . . . . . . . 15
 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
 8. Changes from RFC 3291 to RFC 4001 . . . . . . . . . . . . . . 18
 9. Changes from RFC 2851 to RFC 3291 . . . . . . . . . . . . . . 18
 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
 10.1. Normative References . . . . . . . . . . . . . . . . . . 19
 10.2. Informative References . . . . . . . . . . . . . . . . . 20
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
 Several standards-track MIB modules use the IpAddress SMIv2 base
 type. This limits the applicability of these MIB modules to IP
 Version 4 (IPv4), as the IpAddress SMIv2 base type can only contain
 4-byte IPv4 addresses. The IpAddress SMIv2 base type has become
 problematic with the introduction of IP Version 6 (IPv6) addresses
 [RFC3513].
 This document defines multiple textual conventions (TCs) as a means
 to express generic Internet network layer addresses within MIB module
 specifications. The solution is compatible with SMIv2 (STD 58) and
 SMIv1 (STD 16). New MIB definitions that have to express network
 layer Internet addresses SHOULD use the textual conventions defined
 in this memo. New MIB modules SHOULD NOT use the SMIv2 IpAddress
 base type anymore.
 A generic Internet address consists of two objects: one whose syntax
 is InetAddressType, and another whose syntax is InetAddress. The
 value of the first object determines how the value of the second is
 encoded. The InetAddress textual convention represents an opaque
 Internet address value. The InetAddressType enumeration is used to
 "cast" the InetAddress value into a concrete textual convention for
 the address type. This usage of multiple textual conventions allows
 expression of the display characteristics of each address type and
 makes the set of defined Internet address types extensible.
 The textual conventions for well-known transport domains support
 scoped Internet addresses. The scope of an Internet address is a
 topological span within which the address may be used as a unique
 identifier for an interface or set of interfaces. A scope zone (or,
 simply, a zone) is a concrete connected region of topology of a given
 scope. Note that a zone is a particular instance of a topological
 region, whereas a scope is the size of a topological region
 [RFC4007]. Since Internet addresses on devices that connect multiple
 zones are not necessarily unique, an additional zone index is needed
 on these devices to select an interface. The textual conventions
 InetAddressIPv4z and InetAddressIPv6z are provided to support
 Internet addresses that include a zone index. To support arbitrary
 combinations of scoped Internet addresses, MIB authors SHOULD use a
 separate InetAddressType object for each InetAddress object.
 The textual conventions defined in this document can also be used to
 represent generic Internet subnets and Internet address ranges. A
 generic Internet subnet is represented by three objects: one whose
 syntax is InetAddressType, a second one whose syntax is InetAddress,
 and a third one whose syntax is InetAddressPrefixLength. The
 InetAddressType value again determines the concrete format of the
 InetAddress value, whereas the InetAddressPrefixLength identifies the
 Internet network address prefix.
 A generic range of consecutive Internet addresses is represented by
 three objects. The first one has the syntax InetAddressType, and the
 remaining objects have the syntax InetAddress and specify the start
 and end of the address range. Again, the InetAddressType value
 determines the format of the InetAddress values.
 The textual conventions defined in this document can be used to
 define Internet addresses by using DNS domain names in addition to
 IPv4 and IPv6 addresses. A MIB designer can write compliance
 statements to express that only a subset of the possible address
 types must be supported by a compliant implementation.
 MIB developers who need to represent Internet addresses SHOULD use
 these definitions whenever applicable, as opposed to defining their
 own constructs. Even MIB modules that only need to represent IPv4 or
 IPv6 addresses SHOULD use the InetAddressType/InetAddress textual
 conventions defined in this memo.
 There are many widely deployed MIB modules that use IPv4 addresses
 and that have to be revised to support IPv6. These MIB modules can
 be categorized as follows:
 1. MIB modules that define management information that is, in
 principle, IP version neutral, but the MIB currently uses
 addressing constructs specific to a certain IP version.
 2. MIB modules that define management information that is specific
 to a particular IP version (either IPv4 or IPv6) and that is very
 unlikely to ever be applicable to another IP version.
 MIB modules of the first type SHOULD provide object definitions
 (e.g., tables) that work with all versions of IP. In particular,
 when revising a MIB module that contains IPv4 specific tables, it is
 suggested to define new tables using the textual conventions defined
 in this memo that support all versions of IP. The status of the new
 tables SHOULD be "current", whereas the status of the old IP version
 specific tables SHOULD be changed to "deprecated". The other
 approach, of having multiple similar tables for different IP
 versions, is strongly discouraged.
 MIB modules of the second type, which are inherently IP version
 specific, do not need to be redefined. Note that even in this case,
 any additions to these MIB modules or to new IP version specific MIB
 modules SHOULD use the textual conventions defined in this memo.
 MIB developers SHOULD NOT use the textual conventions defined in this
 document to represent generic transport layer addresses. A special
 set of textual conventions for this purpose is defined in RFC 3419
 [RFC3419].
 The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY",
 in this document are to be interpreted as described in RFC 2119
 [RFC2119].
2. The Internet-Standard Management Framework
 For a detailed overview of the documents that describe the current
 Internet-Standard Management Framework, please refer to section 7 of
 RFC 3410 [RFC3410].
 Managed objects are accessed via a virtual information store, termed
 the Management Information Base or MIB. MIB objects are generally
 accessed through the Simple Network Management Protocol (SNMP).
 Objects in the MIB are defined using the mechanisms defined in the
 Structure of Management Information (SMI). This memo specifies a MIB
 module that is compliant to the SMIv2, which is described in STD 58,
 RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
 [RFC2580].
3. Definitions
INET-ADDRESS-MIB DEFINITIONS ::= BEGIN
IMPORTS
 MODULE-IDENTITY, mib-2, Unsigned32 FROM SNMPv2-SMI
 TEXTUAL-CONVENTION FROM SNMPv2-TC;
inetAddressMIB MODULE-IDENTITY
 LAST-UPDATED "200502040000Z"
 ORGANIZATION
 "IETF Operations and Management Area"
 CONTACT-INFO
 "Juergen Schoenwaelder (Editor)
 International University Bremen
 P.O. Box 750 561
 28725 Bremen, Germany
 Phone: +49 421 200-3587
 EMail: j.schoenwaelder@iu-bremen.de
 Send comments to <ietfmibs@ops.ietf.org>."
 DESCRIPTION
 "This MIB module defines textual conventions for
 representing Internet addresses. An Internet
 address can be an IPv4 address, an IPv6 address,
 or a DNS domain name. This module also defines
 textual conventions for Internet port numbers,
 autonomous system numbers, and the length of an
 Internet address prefix.
 Copyright (C) The Internet Society (2005). This version
 of this MIB module is part of RFC 4001, see the RFC
 itself for full legal notices."
 REVISION "200502040000Z"
 DESCRIPTION
 "Third version, published as RFC 4001. This revision
 introduces the InetZoneIndex, InetScopeType, and
 InetVersion textual conventions."
 REVISION "200205090000Z"
 DESCRIPTION
 "Second version, published as RFC 3291. This
 revision contains several clarifications and
 introduces several new textual conventions:
 InetAddressPrefixLength, InetPortNumber,
 InetAutonomousSystemNumber, InetAddressIPv4z,
 and InetAddressIPv6z."
 REVISION "200006080000Z"
 DESCRIPTION
 "Initial version, published as RFC 2851."
 ::= { mib-2 76 }
InetAddressType ::= TEXTUAL-CONVENTION
 STATUS current
 DESCRIPTION
 "A value that represents a type of Internet address.
 unknown(0) An unknown address type. This value MUST
 be used if the value of the corresponding
 InetAddress object is a zero-length string.
 It may also be used to indicate an IP address
 that is not in one of the formats defined
 below.
 ipv4(1) An IPv4 address as defined by the
 InetAddressIPv4 textual convention.
 ipv6(2) An IPv6 address as defined by the
 InetAddressIPv6 textual convention.
 ipv4z(3) A non-global IPv4 address including a zone
 index as defined by the InetAddressIPv4z
 textual convention.
 ipv6z(4) A non-global IPv6 address including a zone
 index as defined by the InetAddressIPv6z
 textual convention.
 dns(16) A DNS domain name as defined by the
 InetAddressDNS textual convention.
 Each definition of a concrete InetAddressType value must be
 accompanied by a definition of a textual convention for use
 with that InetAddressType.
 To support future extensions, the InetAddressType textual
 convention SHOULD NOT be sub-typed in object type definitions.
 It MAY be sub-typed in compliance statements in order to
 require only a subset of these address types for a compliant
 implementation.
 Implementations must ensure that InetAddressType objects
 and any dependent objects (e.g., InetAddress objects) are
 consistent. An inconsistentValue error must be generated
 if an attempt to change an InetAddressType object would,
 for example, lead to an undefined InetAddress value. In
 particular, InetAddressType/InetAddress pairs must be
 changed together if the address type changes (e.g., from
 ipv6(2) to ipv4(1))."
 SYNTAX INTEGER {
 unknown(0),
 ipv4(1),
 ipv6(2),
 ipv4z(3),
 ipv6z(4),
 dns(16)
 }
InetAddress ::= TEXTUAL-CONVENTION
 STATUS current
 DESCRIPTION
 "Denotes a generic Internet address.
 An InetAddress value is always interpreted within the context
 of an InetAddressType value. Every usage of the InetAddress
 textual convention is required to specify the InetAddressType
 object that provides the context. It is suggested that the
 InetAddressType object be logically registered before the
 object(s) that use the InetAddress textual convention, if
 they appear in the same logical row.
 The value of an InetAddress object must always be
 consistent with the value of the associated InetAddressType
 object. Attempts to set an InetAddress object to a value
 inconsistent with the associated InetAddressType
 must fail with an inconsistentValue error.
 When this textual convention is used as the syntax of an
 index object, there may be issues with the limit of 128
 sub-identifiers specified in SMIv2, STD 58. In this case,
 the object definition MUST include a 'SIZE' clause to
 limit the number of potential instance sub-identifiers;
 otherwise the applicable constraints MUST be stated in
 the appropriate conceptual row DESCRIPTION clauses, or
 in the surrounding documentation if there is no single
 DESCRIPTION clause that is appropriate."
 SYNTAX OCTET STRING (SIZE (0..255))
InetAddressIPv4 ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "1d.1d.1d.1d"
 STATUS current
 DESCRIPTION
 "Represents an IPv4 network address:
 Octets Contents Encoding
 1-4 IPv4 address network-byte order
 The corresponding InetAddressType value is ipv4(1).
 This textual convention SHOULD NOT be used directly in object
 definitions, as it restricts addresses to a specific format.
 However, if it is used, it MAY be used either on its own or in
 conjunction with InetAddressType, as a pair."
 SYNTAX OCTET STRING (SIZE (4))
InetAddressIPv6 ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "2x:2x:2x:2x:2x:2x:2x:2x"
 STATUS current
 DESCRIPTION
 "Represents an IPv6 network address:
 Octets Contents Encoding
 1-16 IPv6 address network-byte order
 The corresponding InetAddressType value is ipv6(2).
 This textual convention SHOULD NOT be used directly in object
 definitions, as it restricts addresses to a specific format.
 However, if it is used, it MAY be used either on its own or in
 conjunction with InetAddressType, as a pair."
 SYNTAX OCTET STRING (SIZE (16))
InetAddressIPv4z ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "1d.1d.1d.1d%4d"
 STATUS current
 DESCRIPTION
 "Represents a non-global IPv4 network address, together
 with its zone index:
 Octets Contents Encoding
 1-4 IPv4 address network-byte order
 5-8 zone index network-byte order
 The corresponding InetAddressType value is ipv4z(3).
 The zone index (bytes 5-8) is used to disambiguate identical
 address values on nodes that have interfaces attached to
 different zones of the same scope. The zone index may contain
 the special value 0, which refers to the default zone for each
 scope.
 This textual convention SHOULD NOT be used directly in object
 definitions, as it restricts addresses to a specific format.
 However, if it is used, it MAY be used either on its own or in
 conjunction with InetAddressType, as a pair."
 SYNTAX OCTET STRING (SIZE (8))
InetAddressIPv6z ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "2x:2x:2x:2x:2x:2x:2x:2x%4d"
 STATUS current
 DESCRIPTION
 "Represents a non-global IPv6 network address, together
 with its zone index:
 Octets Contents Encoding
 1-16 IPv6 address network-byte order
 17-20 zone index network-byte order
 The corresponding InetAddressType value is ipv6z(4).
 The zone index (bytes 17-20) is used to disambiguate
 identical address values on nodes that have interfaces
 attached to different zones of the same scope. The zone index
 may contain the special value 0, which refers to the default
 zone for each scope.
 This textual convention SHOULD NOT be used directly in object
 definitions, as it restricts addresses to a specific format.
 However, if it is used, it MAY be used either on its own or in
 conjunction with InetAddressType, as a pair."
 SYNTAX OCTET STRING (SIZE (20))
InetAddressDNS ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "255a"
 STATUS current
 DESCRIPTION
 "Represents a DNS domain name. The name SHOULD be fully
 qualified whenever possible.
 The corresponding InetAddressType is dns(16).
 The DESCRIPTION clause of InetAddress objects that may have
 InetAddressDNS values MUST fully describe how (and when)
 these names are to be resolved to IP addresses.
 The resolution of an InetAddressDNS value may require to
 query multiple DNS records (e.g., A for IPv4 and AAAA for
 IPv6). The order of the resolution process and which DNS
 record takes precedence depends on the configuration of the
 resolver.
 This textual convention SHOULD NOT be used directly in object
 definitions, as it restricts addresses to a specific format.
 However, if it is used, it MAY be used either on its own or in
 conjunction with InetAddressType, as a pair."
 SYNTAX OCTET STRING (SIZE (1..255))
InetAddressPrefixLength ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "d"
 STATUS current
 DESCRIPTION
 "Denotes the length of a generic Internet network address
 prefix. A value of n corresponds to an IP address mask
 that has n contiguous 1-bits from the most significant
 bit (MSB), with all other bits set to 0.
 An InetAddressPrefixLength value is always interpreted within
 the context of an InetAddressType value. Every usage of the
 InetAddressPrefixLength textual convention is required to
 specify the InetAddressType object that provides the
 context. It is suggested that the InetAddressType object be
 logically registered before the object(s) that use the
 InetAddressPrefixLength textual convention, if they appear
 in the same logical row.
 InetAddressPrefixLength values larger than
 the maximum length of an IP address for a specific
 InetAddressType are treated as the maximum significant
 value applicable for the InetAddressType. The maximum
 significant value is 32 for the InetAddressType
 'ipv4(1)' and 'ipv4z(3)' and 128 for the InetAddressType
 'ipv6(2)' and 'ipv6z(4)'. The maximum significant value
 for the InetAddressType 'dns(16)' is 0.
 The value zero is object-specific and must be defined as
 part of the description of any object that uses this
 syntax. Examples of the usage of zero might include
 situations where the Internet network address prefix
 is unknown or does not apply.
 The upper bound of the prefix length has been chosen to
 be consistent with the maximum size of an InetAddress."
 SYNTAX Unsigned32 (0..2040)
InetPortNumber ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "d"
 STATUS current
 DESCRIPTION
 "Represents a 16 bit port number of an Internet transport
 layer protocol. Port numbers are assigned by IANA. A
 current list of all assignments is available from
 <http://www.iana.org/>.
 The value zero is object-specific and must be defined as
 part of the description of any object that uses this
 syntax. Examples of the usage of zero might include
 situations where a port number is unknown, or when the
 value zero is used as a wildcard in a filter."
 REFERENCE "STD 6 (RFC 768), STD 7 (RFC 793) and RFC 2960"
 SYNTAX Unsigned32 (0..65535)
InetAutonomousSystemNumber ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "d"
 STATUS current
 DESCRIPTION
 "Represents an autonomous system number that identifies an
 Autonomous System (AS). An AS is a set of routers under a
 single technical administration, using an interior gateway
 protocol and common metrics to route packets within the AS,
 and using an exterior gateway protocol to route packets to
 other ASes'. IANA maintains the AS number space and has
 delegated large parts to the regional registries.
 Autonomous system numbers are currently limited to 16 bits
 (0..65535). There is, however, work in progress to enlarge the
 autonomous system number space to 32 bits. Therefore, this
 textual convention uses an Unsigned32 value without a
 range restriction in order to support a larger autonomous
 system number space."
 REFERENCE "RFC 1771, RFC 1930"
 SYNTAX Unsigned32
InetScopeType ::= TEXTUAL-CONVENTION
 STATUS current
 DESCRIPTION
 "Represents a scope type. This textual convention can be used
 in cases where a MIB has to represent different scope types
 and there is no context information, such as an InetAddress
 object, that implicitly defines the scope type.
 Note that not all possible values have been assigned yet, but
 they may be assigned in future revisions of this specification.
 Applications should therefore be able to deal with values
 not yet assigned."
 REFERENCE "RFC 3513"
 SYNTAX INTEGER {
 -- reserved(0),
 interfaceLocal(1),
 linkLocal(2),
 subnetLocal(3),
 adminLocal(4),
 siteLocal(5), -- site-local unicast addresses
 -- have been deprecated by RFC 3879
 -- unassigned(6),
 -- unassigned(7),
 organizationLocal(8),
 -- unassigned(9),
 -- unassigned(10),
 -- unassigned(11),
 -- unassigned(12),
 -- unassigned(13),
 global(14)
 -- reserved(15)
 }
InetZoneIndex ::= TEXTUAL-CONVENTION
 DISPLAY-HINT "d"
 STATUS current
 DESCRIPTION
 "A zone index identifies an instance of a zone of a
 specific scope.
 The zone index MUST disambiguate identical address
 values. For link-local addresses, the zone index will
 typically be the interface index (ifIndex as defined in the
 IF-MIB) of the interface on which the address is configured.
 The zone index may contain the special value 0, which refers
 to the default zone. The default zone may be used in cases
 where the valid zone index is not known (e.g., when a
 management application has to write a link-local IPv6
 address without knowing the interface index value). The
 default zone SHOULD NOT be used as an easy way out in
 cases where the zone index for a non-global IPv6 address
 is known."
 REFERENCE "RFC4007"
 SYNTAX Unsigned32
InetVersion ::= TEXTUAL-CONVENTION
 STATUS current
 DESCRIPTION
 "A value representing a version of the IP protocol.
 unknown(0) An unknown or unspecified version of the IP
 protocol.
 ipv4(1) The IPv4 protocol as defined in RFC 791 (STD 5).
 ipv6(2) The IPv6 protocol as defined in RFC 2460.
 Note that this textual convention SHOULD NOT be used to
 distinguish different address types associated with IP
 protocols. The InetAddressType has been designed for this
 purpose."
 REFERENCE "RFC 791, RFC 2460"
 SYNTAX INTEGER {
 unknown(0),
 ipv4(1),
 ipv6(2)
 }
END
4. Usage Hints
 The InetAddressType and InetAddress textual conventions have been
 introduced to avoid over-constraining an object definition by the use
 of the IpAddress SMI base type, which is IPv4 specific. An
 InetAddressType/InetAddress pair can represent IP addresses in
 various formats.
 The InetAddressType and InetAddress objects SHOULD NOT be sub-typed
 in object definitions. Sub-typing binds the MIB module to specific
 address formats, which may cause serious problems if new address
 formats need to be introduced. Note that it is possible to write
 compliance statements indicating that only a subset of the defined
 address types must be implemented to be compliant.
 Every usage of the InetAddress or InetAddressPrefixLength textual
 conventions must specify which InetAddressType object provides the
 context for the interpretation of the InetAddress or
 InetAddressPrefixLength textual convention.
 It is suggested that the InetAddressType object is logically
 registered before the object(s) that use(s) the InetAddress or
 InetAddressPrefixLength textual convention. An InetAddressType
 object is logically registered before an InetAddress or
 InetAddressPrefixLength object if it appears before the InetAddress
 or InetAddressPrefixLength object in the conceptual row (which
 includes any index objects). This rule allows programs such as MIB
 compilers to identify the InetAddressType of a given InetAddress or
 InetAddressPrefixLength object by searching for the InetAddressType
 object, which precedes an InetAddress or InetAddressPrefixLength
 object.
4.1. Table Indexing
 When a generic Internet address is used as an index, both the
 InetAddressType and InetAddress objects MUST be used. The
 InetAddressType object MUST be listed before the InetAddress object
 in the INDEX clause.
 The IMPLIED keyword MUST NOT be used for an object of type
 InetAddress in an INDEX clause. Instance sub-identifiers are then of
 the form T.N.O1.O2...On, where T is the value of the InetAddressType
 object, O1...On are the octets in the InetAddress object, and N is
 the number of those octets.
 There is a meaningful lexicographical ordering to tables indexed in
 this fashion. Command generator applications may look up specific
 addresses of known type and value, issue GetNext requests for
 addresses of a single type, or issue GetNext requests for a specific
 type and address prefix.
4.2. Uniqueness of Addresses
 IPv4 addresses were intended to be globally unique, current usage
 notwithstanding. IPv6 addresses were architected to have different
 scopes and hence uniqueness [RFC3513]. In particular, IPv6 "link-
 local" unicast addresses are not guaranteed to be unique on any
 particular node. In such cases, the duplicate addresses must be
 configured on different interfaces. So the combination of an IPv6
 address and a zone index is unique [RFC4007].
 The InetAddressIPv6 textual convention has been defined to represent
 global IPv6 addresses and non-global IPv6 addresses in cases where no
 zone index is needed (e.g., on end hosts with a single interface).
 The InetAddressIPv6z textual convention has been defined to represent
 non-global IPv6 addresses in cases where a zone index is needed
 (e.g., a router connecting multiple zones). Therefore, MIB designers
 who use InetAddressType/InetAddress pairs do not need to define
 additional objects in order to support non-global addresses on nodes
 that connect multiple zones.
 The InetAddressIPv4z is intended for use in MIB modules (such as the
 TCP-MIB) which report addresses in the address family used on the
 wire, but where the entity instrumented obtains these addresses from
 applications or administrators in a form that includes a zone index,
 such as v4-mapped IPv6 addresses.
 The size of the zone index has been chosen so that it is consistent
 with (i) the numerical zone index, defined in [RFC4007], and (ii) the
 sin6_scope_id field of the sockaddr_in6 structure, defined in RFC
 2553 [RFC2553].
4.3. Multiple Addresses per Host
 A single host system may be configured with multiple addresses (IPv4
 or IPv6), and possibly with multiple DNS names. Thus it is possible
 for a single host system to be accessible by multiple
 InetAddressType/InetAddress pairs.
 If this could be an implementation or usage issue, the DESCRIPTION
 clause of the relevant objects must fully describe which address is
 reported in a given InetAddressType/InetAddress pair.
4.4. Resolving DNS Names
 DNS names MUST be resolved to IP addresses when communication with
 the named host is required. This raises a temporal aspect to
 defining MIB objects whose value is a DNS name: When is the name
 translated to an address?
 For example, consider an object defined to indicate a forwarding
 destination, and whose value is a DNS name. When does the forwarding
 entity resolve the DNS name? Each time forwarding occurs, or just
 once when the object was instantiated?
 The DESCRIPTION clause of these objects SHOULD precisely define how
 and when any required name to address resolution is done.
 Similarly, the DESCRIPTION clause of these objects SHOULD precisely
 define how and when a reverse lookup is being done, if an agent has
 accessed instrumentation that knows about an IP address, and if the
 MIB module or implementation requires it to map the IP address to a
 DNS name.
5. Table Indexing Example
 This example shows a table listing communication peers that are
 identified by either an IPv4 address, an IPv6 address, or a DNS name.
 The table definition also prohibits entries with an empty address
 (whose type would be "unknown"). The size of a DNS name is limited
 to 64 characters in order to satisfy OID length constraints.
peerTable OBJECT-TYPE
 SYNTAX SEQUENCE OF PeerEntry
 MAX-ACCESS not-accessible
 STATUS current
 DESCRIPTION
 "A list of communication peers."
 ::= { somewhere 1 }
peerEntry OBJECT-TYPE
 SYNTAX PeerEntry
 MAX-ACCESS not-accessible
 STATUS current
 DESCRIPTION
 "An entry containing information about a particular peer."
 INDEX { peerAddressType, peerAddress }
 ::= { peerTable 1 }
PeerEntry ::= SEQUENCE {
 peerAddressType InetAddressType,
 peerAddress InetAddress,
 peerStatus INTEGER
}
peerAddressType OBJECT-TYPE
 SYNTAX InetAddressType
 MAX-ACCESS not-accessible
 STATUS current
 DESCRIPTION
 "The type of Internet address by which the peer
 is reachable."
 ::= { peerEntry 1 }
peerAddress OBJECT-TYPE
 SYNTAX InetAddress (SIZE (1..64))
 MAX-ACCESS not-accessible
 STATUS current
 DESCRIPTION
 "The Internet address for the peer. The type of this
 address is determined by the value of the peerAddressType
 object. Note that implementations must limit themselves
 to a single entry in this table per reachable peer.
 The peerAddress may not be empty due to the SIZE
 restriction.
 If a row is created administratively by an SNMP
 operation and the address type value is dns(16), then
 the agent stores the DNS name internally. A DNS name
 lookup must be performed on the internally stored DNS
 name whenever it is being used to contact the peer.
 If a row is created by the managed entity itself and
 the address type value is dns(16), then the agent
 stores the IP address internally. A DNS reverse lookup
 must be performed on the internally stored IP address
 whenever the value is retrieved via SNMP."
 ::= { peerEntry 2 }
 The following compliance statement specifies that compliant
 implementations need only support IPv4/IPv6 addresses without zone
 indices. Support for DNS names or IPv4/IPv6 addresses with zone
 indices is not required.
 peerCompliance MODULE-COMPLIANCE
 STATUS current
 DESCRIPTION
 "The compliance statement of the peer MIB."
 MODULE -- this module
 MANDATORY-GROUPS { peerGroup }
 OBJECT peerAddressType
 SYNTAX InetAddressType { ipv4(1), ipv6(2) }
 DESCRIPTION
 "An implementation is only required to support IPv4
 and IPv6 addresses without zone indices."
 ::= { somewhere 2 }
 Note that the SMIv2 does not permit inclusion of objects that are not
 accessible in an object group (see section 3.1 in STD 58, RFC 2580
 [RFC2580]). It is therefore not possible to refine the syntax of
 auxiliary objects that are not accessible. It is suggested that the
 refinement be expressed informally in the DESCRIPTION clause of the
 MODULE-COMPLIANCE macro invocation.
6. Security Considerations
 This module does not define any management objects. Instead, it
 defines a set of textual conventions which may be used by other MIB
 modules to define management objects.
 Meaningful security considerations can only be written in the MIB
 modules that define management objects. This document has therefore
 no impact on the security of the Internet.
7. Acknowledgments
 This document was produced by the Operations and Management Area
 "IPv6MIB" design team. For their comments and suggestions, the
 authors would like to thank Fred Baker, Randy Bush, Richard Draves,
 Mark Ellison, Bill Fenner, Jun-ichiro Hagino, Mike Heard, Tim
 Jenkins, Allison Mankin, Glenn Mansfield, Keith McCloghrie, Thomas
 Narten, Erik Nordmark, Peder Chr. Norgaard, Randy Presuhn, Andrew
 Smith, Dave Thaler, Kenneth White, Bert Wijnen, and Brian Zill.
8. Changes from RFC 3291 to RFC 4001
 The following changes have been made relative to RFC 3291:
 o Added a range restriction to the InetAddressPrefixLength textual
 convention.
 o Added new textual conventions InetZoneIndex, InetScopeType, and
 InetVersion.
 o Added explicit "d" DISPLAY-HINTs for textual conventions that did
 not have them.
 o Updated boilerplate text and references.
9. Changes from RFC 2851 to RFC 3291
 The following changes have been made relative to RFC 2851:
 o Added new textual conventions InetAddressPrefixLength,
 InetPortNumber, and InetAutonomousSystemNumber.
 o Rewrote the introduction to say clearly that, in general, one
 should define MIB tables that work with all versions of IP. The
 other approach of multiple tables for different IP versions is
 strongly discouraged.
 o Added text to the InetAddressType and InetAddress descriptions
 requiring that implementations must reject set operations with an
 inconsistentValue error if they lead to inconsistencies.
 o Removed the strict ordering constraints. Description clauses now
 must explain which InetAddressType object provides the context for
 an InetAddress or InetAddressPrefixLength object.
 o Aligned wordings with the IPv6 scoping architecture document.
 o Split the InetAddressIPv6 textual convention into the two textual
 conventions (InetAddressIPv6 and InetAddressIPv6z) and introduced
 a new textual convention InetAddressIPv4z. Added ipv4z(3) and
 ipv6z(4) named numbers to the InetAddressType enumeration.
 Motivations for this change: (i) to enable the introduction of a
 textual conventions for non-global IPv4 addresses, (ii) alignment
 with the textual conventions for transport addresses, (iii)
 simpler compliance statements in cases where support for IPv6
 addresses with zone indices is not required, and (iv) to simplify
 implementations for host systems that will never have to report
 zone indices.
10. References
10.1. Normative References
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2578] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
 "Structure of Management Information Version 2 (SMIv2)",
 STD 58, RFC 2578, April 1999.
 [RFC2579] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
 "Textual Conventions for SMIv2", STD 58, RFC 2579, April
 1999.
 [RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
 "Conformance Statements for SMIv2", STD 58, RFC 2580,
 April 1999.
 [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
 (IPv6) Addressing Architecture", RFC 3513, April 2003.
 [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
 B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
 February 2005.
10.2. Informative References
 [RFC2553] Gilligan, R., Thomson, S., Bound, J., and W. Stevens,
 "Basic Socket Interface Extensions for IPv6", RFC 2553,
 March 1999.
 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
 MIB", RFC 2863, June 2000.
 [RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
 "Introduction and Applicability Statements for Internet-
 Standard Management Framework", RFC 3410, December 2002.
 [RFC3419] Daniele, M. and J. Schoenwaelder, "Textual Conventions for
 Transport Addresses", RFC 3419, December 2002.
Authors' Addresses
 Michael Daniele
 SyAM Software, Inc.
 1 Chestnut St, Suite 3-I
 Nashua, NH 03060
 USA
 Phone: +1 603 598-9575
 EMail: michael.daniele@syamsoftware.com
 Brian Haberman
 Johns Hopkins University Applied Physics Laboratory
 11100 Johns Hopkins Road
 Laurel, MD 20723-6099
 USA
 Phone: +1-443-778-1319
 EMail: brian@innovationslab.net
 Shawn A. Routhier
 Wind River Systems, Inc.
 500 Wind River Way
 Alameda, CA 94501
 USA
 Phone: +1 510 749-2095
 EMail: shawn.routhier@windriver.com
 Juergen Schoenwaelder
 International University Bremen
 P.O. Box 750 561
 28725 Bremen
 Germany
 Phone: +49 421 200-3587
 EMail: j.schoenwaelder@iu-bremen.de
Full Copyright Statement
 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and at www.rfc-editor.org, 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 ISOC's procedures with respect to rights in ISOC 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.