Attribute-Value Pairs For Provisioning Customer Equipment Supporting IPv4-Over-IPv6 Transitional Solutions

A number of transition techniques have been defined to allow IPv4 packets to pass between hosts and IPv4 networks over an intervening IPv6 network while minimizing the number of public IPv4 addresses that need to be consumed by the hosts. Different operators will deploy different technologies, and sometimes one operator will use more than one technology, depending on what is supported by the available equipment and upon other factors both technical and economic. Each technique requires the provisioning of some subscriber-specific information on the customer edge device. The provisioning may be by DHCPv6 or by some other method. This document is indifferent to the specific provisioning technique used, but assumes a deployment in which that information is managed by AAA (Authentication, Authorization, and Accounting) servers. It further assumes that this information is delivered to intermediate network nodes for onward provisioning using the Diameter protocol . As described below, in the particular case where the Lightweight 4over6 (lw4o6) transition method has been deployed, per-subscriber-site information almost identical to that passed to the subscriber site also needs to be delivered to the border router serving that site. The Diameter protocol may be used for this purpose too. This document analyzes the information required to configure the customer edge equipment for the following set of transition methods: Dual-Stack Lite (DS-Lite) , Lightweight 4over6 (lw4o6) , and Mapping of Address and Port with Encapsulation (MAP-E) . specifies a generic solution for delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution was developed with DS-Lite in mind but it is however not limited to DS-Lite. As such, it applies also for lw4o6 and MAP-E. This document analyzes the information required to configure the customer edge equipment for the support of multicast in the context of DS-Lite, MAP-E, and Lightweight 4over6 in particular. On the basis of those analyses it specifies a number of attribute-value pairs (AVPs) to allow the necessary subscriber-site-specific configuration information to be carried in Diameter. This document doesn't specify any new commands or Application-Ids. The specified AVPs could be used for any Diameter application suitable for provisioning.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . The abbreviation "CE" denotes the equipment at the customer edge that terminates the customer end of an IPv6 transitional tunnel. This will usually be a router, but could be a host directly connected to the network. The term "tunnel source address" is used to denote the IPv6 source address used in the outer header of packets sent from the CE through an lw4o6 transitional tunnel to the border router.

This section reviews the parameters that need to be provisioned for each of the transition methods listed above. This enumeration provides the justification for the AVPs defined in the next section. A means is required to indicate which transition method(s) a given subscriber wants to use. The approach taken in this document is to specify Grouped AVPs specific to lw4o6 and MAP-E. The operator can control which of these two transition methods a given subscriber uses by ensuring that AAA passes only the Grouped AVP relevant to that method. A Grouped AVP is unnecessary for Dual-Stack Lite, since AAA has only to provide the Fully Qualified Domain Name (FQDN) of the DS-Lite Address Family Transition Router (AFTR) (see ). Hence when no Grouped AVP is provided either for lw4o6 or MAP-E and only the AFTR's FQDN is present, this indicates that the subscriber equipment will use the Dual-Stack Lite transition method. Provisioning of multicast is an orthogonal activity, since it is independent of the transition method.

DS-Lite is documented in . The Basic Bridging BroadBand (B4) element at the customer premises needs to discover the IPv6 address of the AFTR (border router). For the reasons discussed in , the AAA server provisions the B4 element with the AFTR's Fully Qualified Domain Name (FQDN) that is passed to a B4's IP resolution library. The AFTR's FQDN is contained in the Border-Router-Name AVP (see ). The B4 element could also be configured with the IPv4 address of the B4 interface facing the tunnel, with valid values from 192.0.0.2 to 192.0.0.7 and the default value of 192.0.0.2 in the absence of provisioning. Provisioning such information through AAA is problematic because it is most likely used in a case where multiple B4 instances occupy the same device. This document therefore assumes that the B4 interface address is determined by other means than AAA (implementation-dependent or static assignment).

Lightweight 4over6 (lw4o6) is documented in . Lw4o6 requires four items to be provisioned to the customer equipment: IPv6 address of the border router. IPv6 prefix used by the CE to construct the tunnel source address. In the terminology of , this is the IPv6 Binding Prefix. an IPv4 address to be used on the external side of the CE; and if the IPv4 address is shared, a specification of the port set the subscriber site is allowed to use. Please see the description in . For lw4o6, all three of the parameters 'a', 'k', and PSID described in that section are required. The default value of the offset parameter 'a' is 0. As discussed in Section 4 of , it is necessary to synchronize this configuration with corresponding per-subscriber configuration at the border router. The border router information consists of the same public IPv4 address and port set parameters that are passed to the CE, bound together with the full /128 IPv6 address (not just the Binding Prefix) configured as the tunnel source address at the CE.

When an external IPv4 address is shared, lw4o6 and MAP-E restrict the CE to use of a subset of all available ports on the external side. Both transition methods use the algorithm defined in Appendix B of to derive the values of the port numbers in the port set. This algorithm features three parameters, describing the positioning and value of the Port Set Identifier (PSID) within each port number of the generated set: an offset 'a' from the beginning of the port number to the first bit of the PSID; the length 'k' of the PSID within the port number, in bits; and the value of the PSID itself.

Mapping of Address and Port with Encapsulation (MAP-E) is described in . MAP-E requires the provisioning of the following per-subscriber information at the customer edge device: the IPv6 address of one or more border routers, or in MAP-E terminology, MAP-E border relays. the unique End-user IPv6 prefix for the customer edge device. This may be provided by AAA or acquired by other means. the Basic Mapping Rule for the customer edge device. This includes the following parameters: the rule IPv6 prefix and length; the rule IPv4 prefix and length. A prefix length of 0 indicates that the entire IPv4 address or prefix is coded in the Extended Address (EA) bits of the End-user IPv6 prefix rather than in the mapping rule. the number of EA bits included in the End-user IPv6 prefix; port set parameters giving the set of ports the CE is allowed to use when the IPv4 address is shared. Please see the description of these parameters in . At a minimum, the offset parameter 'a' is required. For MAP-E this has the default value 6. The parameters 'k' and PSID are needed if they cannot be derived from the mapping rule information and the EA bits (final case of Section 5.2 of ). whether the device is to operate in mesh or hub-and-spoke mode; in mesh mode only, zero or more Forwarding Mapping Rules, described by the same set of parameters as the Basic Mapping Rule; As indicated in Section 5, bullet 1 of , a MAP CE can be provisioned with multiple End-user IPv6 prefixes, each associated with its own Basic Mapping Rule. This does not change the basic requirement for representation of the corresponding information in the form of Diameter AVPs, but adds a potential requirement for multiple instances of this information to be present in the Diameter message, differing in the value of the End-user IPv6 prefix (in contrast to the Forward Mapping Rule instances). The border router needs to be configured with the superset of the Mapping Rules passed to the customer sites it serves. Since this requirement does not require direct coordination with CE configuration in the way lw4o6 does, it is out of scope of the present document. However, the AVPs defined here may be useful if a separate Diameter application is used to configure the border router.

specifies a generic solution for delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution can be in particular deployed in a DS-Lite context, but is also adaptable to lw4o6 and MAP-E. For example, specifies how DHCPv6 can be used to provision multicast-related information. The following lists the multicast-related information that needs to be provisioned: ASM-mPrefix64: the IPv6 multicast prefix to be used to synthesize the IPv4-embedded IPv6 addresses of the multicast groups in the Any-Source Multicast (ASM) mode. This is achieved by concatenating the ASM-mPrefix64 and a IPv4 multicast address; the IPv4 multicast address is inserted in the last 32 bits of the IPv4-embedded IPv6 multicast address. SSM-mPrefix64: the IPv6 multicast prefix to be used to synthesize the IPv4-embedded IPv6 addresses of the multicast groups in the Source-Specific Multicast (SSM, ) mode. This is achieved by concatenating the SSM-mPrefix64 and a IPv4 multicast address; the IPv4 multicast address is inserted in the last 32 bits of the IPv4-embedded IPv6 multicast address. uPrefix64: the IPv6 unicast prefix to be used in SSM mode for constructing the IPv4-embedded IPv6 addresses representing the IPv4 multicast sources in the IPv6 domain. uPrefix64 may also be used to extract the IPv4 address from the received multicast data flows. The address mapping follows the guidelines documented in .

There are two items that are common to the different transition methods, and the corresponding AVPs to carry them can be reused: a representation of the IPv6 address of a border router; A set of prefixes for delivery of multicast services to IPv4 clients over an IPv6 multicast network. sets a precedent for representation of the IPv6 address of a border router as an FQDN. This can be dereferenced to one or more IP addresses by the provisioning system before being passed to the customer equipment, or left as an FQDN as it is in . The remaining requirements are transition-method-specific: for lw4o6, a representation of a binding between (1) either the IPv6 Binding Prefix or a full /128 IPv6 address, (2) a public IPv4 address, and (3) (if the IPv4 address is shared) a port set identifier; for MAP-E, a representation of the unique End-user IPv6 prefix for the CE, if not provided by other means; for MAP-E, a representation of a Mapping Rule; for MAP-E, an indication of whether mesh mode or hub-and-spoke mode is to be used.

This section provides the specifications for the AVPs needed to meet the requirements summarized in .

The IP-Prefix-Length AVP (AVP code TBD00) is of type Unsigned32. It provides the length of an IPv4 or IPv6 prefix. Valid values are from 0 to 32 for IPv4, and from 0 to 128 for IPv6. Tighter limits are given below for particular contexts of use of this AVP. NOTE: The IP-Prefix-Length AVP is only relevant when associated with an IP-Address AVP in a Grouped AVP.

Following on the precedent set by and , this document identifies a border router using an FQDN rather than an address. The Border-Router-Name AVP (AVP Code TBD01) is of type OctetString. The FQDN encoding MUST follow the Name Syntax defined in and are represented in ASCII form. Note, if Internationalized Domain Names (IDNs) are used, A-labels defined in must be used (see Appendix D of ).

The 64-Multicast-Attributes AVP (AVP Code TBD02) is of type Grouped. It contains the multicast-related IPv6 prefixes needed for providing IPv4 multicast over IPv6 using DS-Lite, MAP-E, or lw4o6, as mentioned in . The syntax is shown in .

[ ASM-mPrefix64 ] [ SSM-mPrefix64 ] [ Delegated-IPv6-Prefix ] *[ AVP ] ]]> 64-Multicast-Attributes AVP MUST include the ASM-mPrefix64 AVP or the SSM-mPrefix64 AVP, and it MAY include both. The Delegated-IPv6-Prefix AVP MUST be present when the SSM-mPrefix64 AVP is present. The Delegated-IPv6-Prefix AVP MAY be present when the ASM-mPrefix64 AVP is present.

The ASM-mPrefix64 AVP (AVP Code TBD03) conveys the value of ASM-mPrefix64 as mentioned in . The ASM-mPrefix64 AVP is of type Grouped, as shown in .

{ IP-Address } { IP-Prefix-Length } *[ AVP ] ]]> IP-Address (AVP code 518) is defined in and is of type Address. Within the ASM-mPrefix64 AVP, it provides the value of an IPv6 prefix. The AddressType field in IP-Address MUST have value 2 (IPv6). The conveyed multicast IPv6 prefix MUST belong to the ASM range. Unused bits in IP-Address beyond the actual prefix MUST be set to zeroes by the sender and ignored by the receiver. The IP-Prefix-Length AVP (AVP code TBD00) provides the actual length of the prefix contained in the IP-Address AVP. Within the ASM-mPrefix64 AVP, valid values of the IP-Prefix-Length AVP are from 24 to 96.

The SSM-mPrefix64 AVP (AVP Code TBD04) conveys the value of SSM-mPrefix64 as mentioned in . The SSM-mPrefix64 AVP is of type Grouped, as shown in .

{ IP-Address } { IP-Prefix-Length } *[ AVP ] ]]> IP-Address (AVP code 518) provides the value of an IPv6 prefix. The AddressType field in IP-Address MUST have value 2 (IPv6). The conveyed multicast IPv6 prefix MUST belong to the SSM range. Unused bits in IP-Address beyond the actual prefix MUST be set to zeroes by the sender and ignored by the receiver. The IP-Prefix-Length AVP (AVP code TBD00) provides the actual length of the prefix contained in the IP-Address AVP.

Within the 64-Multicast-Attributes AVP, the Delegated-IPv6-Prefix AVP (AVP Code 123) conveys the value of uPrefix64, a unicast IPv6 prefix, as mentioned in . The Delegated-IPv6-Prefix AVP is defined in . As specified by , the value in the Prefix-Length field MUST be one of 32, 48, 56, 64 or 96.

The Tunnel-Source-Pref-Or-Addr AVP (AVP Code TBD05) conveys either the IPv6 Binding Prefix or the tunnel source address on the CE, as described in . The Tunnel-Source-Pref-Or-Addr AVP is of type Grouped, with syntax as shown in . The Tunnel-Source-Pref-Or-Addr AVP MUST contain either the Delegated-IPv6-Prefix AVP or the Tunnel-Source-IPv6-Address AVP, not both.

[ Delegated-IPv6-Prefix ] [ Tunnel-Source-IPv6-Address ] *[ AVP ] ]]> This AVP is defined separately from the lw4o6-Binding AVP (which includes it) to provide flexibility in the transport of the tunnel source address from the provisioning system to AAA while also supporting the provision of a complete binding to the lw4o6 border router.

The Delegated-IPv6-Prefix AVP (AVP code 123) is of type Octetstring, and is defined in . Within the Tunnel-Source-Pref-Or-Addr AVP, it conveys the IPv6 Binding Prefix assigned to the CE. Valid values in the Prefix-Length field are from 0 to 128 (full address).

The Tunnel-Source-IPv6-Address AVP (AVP code TBD06) is of type Address. It provides the address that the CE has assigned to its end of an lw4o6 tunnel. The AddressType field in this AVP MUST be set to 2 (IPv6).

The Port-Set-Identifier AVP (AVP Code TBD07) is a structured OctetString with four octets of data, hence a total AVP length of 12. The description of the structure which follows refers to refers to the parameters described in (see ). The first (high-order) octet is the Offset field. It is interpreted as an 8-bit unsigned integer giving the offset 'a' from the beginning of a port number to the beginning of the port set identifier (PSID) to which that port belongs. Valid values are from 0 to 15. The next octet, the PSIDLength, is also interpreted as an 8-bit unsigned integer and gives the length 'k' in bits of the port set identifier (PSID). Valid values are from 0 to (16 - a). A value of 0 indicates that the PSID is not present (probable case for MAP-E, see ), and the PSIDValue field MUST be ignored. The final two octets contain the PSIDValue field. They give the value of the PSID itself, right-justified within the field. That is, the value of the PSID occupies the 'k' lowest-order bits of the PSIDValue field.

The Lw4o6-Binding AVP (AVP Code TBD08) is of type Grouped. It contains the elements of configuration that constitute the binding between an lw4o6 tunnel and IPv4 packets sent through that tunnel, as described in .

{ Tunnel-Source-Pref-Or-Addr } { Lw4o6-External-IPv4-Addr } [ Port-Set-Identifier ] *[ AVP ] ]]> The Tunnel-Source-Pref-Or-Addr AVP is defined in and provides either the Binding Prefix or the full IPv6 tunnel source address. The Lw4o6-External-IPv4-Addr AVP is defined in . The Port-Set-Identifier AVP is defined in . It identifies the specific set of ports assigned to the lw4o6 tunnel, when the IPv4 address is being shared.

The Lw4o6-External-IPv4-Addr AVP (AVP Code TBD09) uses the Address derived data format defined in Section 4.3.1 of . It provides the CE's external IPv4 address within the lw4o6 tunnel associated with the given binding. The AddressType field MUST be set to 1 (IPv4), and the total length of the AVP MUST be 14 octets.

The MAP-E-Attributes AVP (AVP Code TBD10) is of type Grouped. It contains the configuration data identified in for all of the mapping rules (Basic and Forwarding) in a single MAP domain. Multiple instances of this AVP will be present if the CE belongs to multiple MAP domains.

1*{ Border-Router-Name } 1*{ MAP-Mapping-Rule } [ MAP-Mesh-Mode ] [ Delegated-IPv6-Prefix ] *[ AVP ] ]]> The Border-Router-Name AVP is defined in . It provides the FQDN of a MAP border relay at the edge of the MAP domain to which the containing MAP-E-Attributes AVP relates. At least one instance of this AVP MUST be present. The MAP-Mapping-Rule AVP is defined in . At least one instance of this AVP MUST be present. If the MAP-E domain supports mesh mode (indicated by the presence of the MAP-Mesh-Mode AVP), additional MAP-Mapping-Rule instances MAY be present. If the MAP-E domain is operating in hub-and-spoke mode, additional MAP-Mapping-Rule instances MUST NOT be present. The MAP-Mesh-Mode AVP is defined in . The absence of the mesh mode indicator attribute indicates that the CE is required to operate in hub-and-spoke mode. The Delegated-IPv6-Prefix AVP (AVP Code 123) provides the End-user IPv6 prefix assigned to the CE for the MAP domain to which the containing MAP-E-Attributes AVP relates. The AVP is defined in . Valid values of the Prefix-Length field range from 0 to 128. The Delegated-IPv6-Prefix AVP is optional because, depending on deployment, the End-user IPv6 prefix may be provided by AAA or by other means. If multiple instances of the MAP-E-Attributes AVP containing the Delegated-IPv6-Prefix AVP are present, each instance of the latter MUST have a different value.

The MAP-Mesh-Mode AVP (AVP Code TBD11) is of type Enumerated and indicates whether the CE has to operate in mesh mode or hub-and-spoke when using MAP-E. The following values are supported: 0 MESH 1 HUB_AND_SPOKE The absence of the mesh mode indicator attribute indicates that the CE is required to operate in hub-and-spoke mode.

The MAP-Mapping-Rule AVP (AVP Code TBD12) is of type Grouped, and is used only in conjunction with MAP-based transition methods. Mapping rules are required both by the MAP border relay and by the CE. The components of the MAP-Mapping-Rule AVP provide the contents of a mapping rule as described in . The syntax of the MAP-Mapping-Rule AVP is as follows:

{ Rule-IPv4-Addr-Or-Prefix } { Rule-IPv6-Prefix } { EA-Field-Length } { Port-Set-Identifier } *[ AVP ] ]]> The Rule-IPv4-Addr-Or-Prefix, Rule-IPv6-Prefix, EA-Field-Length, and Port-Set-Identifier AVPs MUST all be present. The Port-Set-Identifier AVP provides information to identify the specific set of ports assigned to the CE. For more information see and . The Port-Set-Identifier AVP is defined in .

The Rule-IPv4-Addr-Or-Prefix AVP (AVP Code TBD13) conveys the rule IPv4 prefix and length as described in . The Rule-IPv4-Addr-Or-Prefix AVP is of type Grouped, as shown in .

{ IP-Address } { IP-Prefix-Length } *[ AVP ] ]]> IP-Address (AVP code 518) is defined in and is of type Address. Within the Rule-IPv4-Addr-Or-Prefix AVP, it provides the value of a unicast IPv4 address or prefix. The AddressType field in IP-Address MUST have value 1 (IPv4). Unused bits in IP-Address beyond the actual prefix MUST be set to zeroes by the sender and ignored by the receiver. The IP-Prefix-Length AVP (AVP code TBD00) provides the actual length of the prefix contained in the IP-Address AVP. Within the Rule-IPv4-Addr-Or-Prefix AVP, valid values of the IP-Prefix-Length AVP are from 0 to 32 (full address), based on the different cases identified in Section 5.2 of .

The Rule-IPv6-Prefix AVP (AVP Code TBD14) conveys the rule IPv6 prefix and length as described in . The Rule-IPv6-Prefix AVP is of type Grouped, as shown in .

{ IP-Address } { IP-Prefix-Length } *[ AVP ] ]]> IP-Address (AVP code 518) is defined in and is of type Address. Within the Rule-IPv6-Prefix AVP, it provides the value of a unicast IPv6 prefix. The AddressType field in IP- Address MUST have value 2 (IPv6). Unused bits in IP-Address beyond the actual prefix MUST be set to zeroes by the sender and ignored by the receiver. The IP-Prefix-Length AVP (AVP code TBD00) provides the actual length of the prefix contained in the IP-Address AVP. Within the Rule-IPv6-Prefix AVP, the minimum valid prefix length is 0. The maximum value is bounded by the length of the End-user IPv6 prefix associated with the mapping rule, if present in the form of the Delegated-IPv6-Prefix AVP in the enclosing MAP-E-Attributes AVP. Otherwise the maximum value is 128.

The EA-Field-Length AVP (AVP Code TBD15) is of type Unsigned32. Valid values range from 0 to 48. See Section 5.2 of for a description of the use of this parameter in deriving IPv4 address and port number configuration.

As described in the Diameter base protocol , the M-bit usage for a given AVP in a given command may be defined by the application.

This memo requests to IANA to register the following Diameter AVP codes: Code Attribute Name Reference TBD00 IP-Prefix-Length This document TBD01 Border-Router-Name This document TBD02 64-Multicast-Attributes This document TBD03 ASM-mPrefix64 This document TBD04 SSM-mPrefix64 This document TBD05 Tunnel-Source-Pref-Or-Addr This document TBD06 Tunnel-Source-IPv6-Address This document TBD07 Port-Set-Identifier This document TBD08 Lw4o6-Binding This document TBD09 Lw4o6-External-IPv4-Addr This document TBD10 MAP-E-Attributes This document TBD11 MAP-Mesh-Mode This document TBD12 MAP-Mapping-Rule This document TBD13 Rule-IPv4-Addr-Or-Prefix This document TBD14 Rule-IPv6-Prefix This document TBD15 EA-Field-Length This document

The AVPs defined in this document face two threats, both dependent on man-in-the-middle (MITM) attacks on the Diameter delivery path. The first threat is denial-of-service (DoS) through modification of the AVP contents leading to misconfiguration, e.g., a subscriber may fail to access its connectivity service if an invalid IP address was configured, the subscriber's traffic can be intercepted by a misbehaving node if a fake Border Node has been configured, etc. The second threat is that Diameter security is currently provided on a hop-by-hop basis (see Section 2.2 of ). At the time of writing, the Diameter end-to-end security problem has not been solved, so MITM attacks by Diameter peers along the path are possible. Diameter-related security considerations are discussed in Section 13 of .

Given that the AVPs defined in this document reveal privacy-related information (e.g., subscriber addresses) that can be used for tracking proposes, all these AVPs are considered to be security-sensitive. Therefore the considerations discussed in Section 13.3 of MUST be followed for Diameter messages containing these AVPs.

Huawei Technologies funded Tom Taylor's work on earlier versions of this document. Special thanks to Lionel Morand for the detailed review. Many thanks to Russ Housley, Tim Chown, Spencer Dawkins, and Ben Campbell for the review and comments.