Discovering Provisioning Domain Names and Data
draft-ietf-intarea-provisioning-domains-00

Abstract

An increasing number of hosts and networks are connected to the Internet through multiple interfaces, some of which may provide multiple ways to access the internet by means of multiple IPv6 prefix configurations.

This document describes a way for hosts to retrieve additional information about their network access characteristics. The set of configuration items required to access the Internet is called a Provisioning Domain (PvD). The PvD is identified by a Fully Qualified Domain Name (FQDN). This identifier, retrieved using a new Router Advertisement (RA) option, is associated with the set of information included within the RA and may later be used to retrieve additional information associated with the PvD by way of an HTTP-over-TLS request.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on May 3, 2018.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Provisioning Domain Identification using Router Advertisements
• 3.1. PvD ID Option for Router Advertisements
• 3.2. Router Behavior
• 3.3. Host Behavior
• 3.3.1. DHCPv6 configuration association
• 3.3.2. DHCPv4 configuration association
• 3.3.3. Interconnection Sharing by the Host
• 4. Provisioning Domain Additional Information
• 4.1. Retrieving the PvD Additional Information
• 4.2. Providing the PvD Additional Information
• 4.3. PvD Additional Information Format
• 4.3.1. Connectivity Characteristics Information
• 4.3.2. Private Extensions
• 4.3.3. Example
• 4.4. Detecting misconfiguration and misuse
• 5. Security Considerations
• 6. Privacy Considerations
• 7. IANA Considerations
• 8. Acknowledgements
• 9. Contributor
• 10. References
• 10.1. Normative references
• 10.2. Informative references
• Appendix A. Changelog
• A.1. Version 00
• A.2. Version 01
• A.3. Version 02
• A.4. WG Document version 00
• Appendix B. Connection monetary cost
• B.1. Conditions
• B.2. Price
• B.3. Examples
• Authors' Addresses

1. Introduction

It has become very common in modern networks for hosts to access the network through different network interfaces, tunnels, or next-hop routers. To describe the set of network configurations associated with %% each access method, the concept of Provisioning Domain (PvD) was defined in [RFC7556].

This specification provides a way to identify explicit PvDs with Fully Qualified Domain Names (FQDN). The FQDN is thus called PvD ID in this document. The PvD IDs is included in a Router Advertisement [RFC4861] option. This new option, when present, associates the set of configurations with the PvD ID in the same RA message. It is worth noting that multiple PvDs (with different PvD IDs) could be provisioned on any host interface, as well as noting that the same PvD ID could be used on different interfaces in order to inform the host that all PvDs with the same PvD ID, on different interfaces, ultimately provide identical services.

This document also introduces a way for hosts to retrieve additional information related to a specific PvD by the mean of an HTTP-over-TLS query using an URI derived from the PvD ID. The retrieved JSON object contains additional network information that would typically be considered unfit, or too large, to be directly included in the Router Advertisements. This information can be used by the networking stack, the applications, or even be partially displayed to the users (e.g., by displaying a localized network service name).

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

In addition, this document uses the following terminology:

PvD:

A Provisioning Domain, a set of network configuration information; for more information, see [RFC7556].

PvD ID:

A Fully Qualified Domain Name (FQDN) used to identify a PvD.

Explicit PvD:

A PvD uniquely identified with a PvD ID. for more information, see [RFC7556].

Implicit PvD:

A PvD associated with a set of configuration information that, in the absence of a PvD ID, is associated with the advertising router.

3. Provisioning Domain Identification using Router Advertisements

Each provisioning domain is identified by a PvD ID. The PvD ID is a Fully Qualified Domain Name (FQDN) which MUST belong to the network operator in order to avoid ambiguity. The same PvD ID MAY be used in several access networks when the set of configuration information is identical (e.g. in all home networks subscribed to the same service).

3.1. PvD ID Option for Router Advertisements

This document introduces a Router Advertisement (RA) option called the PvD ID Router Advertisement Option, used to convey the FQDN identifying a given PvD.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |    Length     |H|L|         Reserved          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Sequence            |                             ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                             ...
...                         PvD ID FQDN                       ...
...             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...             |                  Padding                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            

PvD ID Router Advertisements Option format

Type :

(8 bits) To be defined by IANA. Current experimentation uses the value of 253.

Length :

(8 bits) The length of the option (including the Type and Length fields) in units of 8 octets.

H-flag :

(1 bit) Whether some PvD Additional Information is made available through HTTP over TLS, as described in Section 4.

L-flag :

(1 bit) Whether the router is also providing IPv4 information using DHCPv4 (see Section 3.3.2).

Reserved :

(14 bits) Reserved for later use. It MUST be set to zero by the sender and ignored by the receiver.

Sequence :

(16 bits) Sequence number for the PvD Additional Information, as described in Section 4.

PvD ID FQDN :

The FQDN used as PvD ID encoded as described in Section 3.1 of RFC1035. Note that for simple decoding, the domain names MUST NOT be encoded in the compressed form described in Section 4.1.4 of RFC1035. This encoding is the same as the one used in RFC8106. The encoding MUST end with a null (zero-length) label.

Padding :

Zero or more padding octets such as to set the option length (Type and Length fields included) to eight times the value of the Length field. It MUST be set to zero by the sender and ignored by the receiver.

Routers MUST NOT include more than one PvD ID Router Advertisement Option in each RA. In case multiple PvD ID options are found in a given RA, hosts MUST ignore all but the first PvD ID option.

3.2. Router Behavior

A router MAY insert only one PvD ID Option in an RA. The included PvD ID is associated with all the other options included in the same RA (for example, and not limited to: Prefix Information [RFC4861], Recursive DNS Server [RFC8106], Routing Information [RFC4191] options).

In order to provide multiple independent PvDs, a router MUST send multiple RAs using different source link-local addresses (LLA) (as proposed in [I-D.bowbakova-rtgwg-enterprise-pa-multihoming]), each of which MAY include a PvD ID option. In such cases, routers MAY originate the different RAs using the same datalink layer address.

If the router is actually a VRRP instance [RFC5798], then the procedure is identical except that the virtual datalink layer address is used as well as the virtual IPv6 LLA.

3.3. Host Behavior

RAs provide configuration information for IPv6 hosts. When a host receives an RA message including a PvD ID Option, it MUST associate all the configuration objects which are updated by the received RA (the same types as in Section 3.3) with the PvD identified by the PvD ID Option, even if some objects are already associated with a different explicit or implicit PvD. PvD ID are compared in a case-insensitive manner (i.e., A=a), assuming ASCII with zero parity. Non-alphabetic codes must match exactly (see also Section 3.1 of [RFC1035]).

If the received RA does not include a PvD ID Option, the host MUST associate the configuration objects which are updated by the received RA with an implicit PvD, even if some objects were already associated with a different explicit or implicit PvD. This implicit PvD MUST be identified by the LLA of the router sending the RA and the interface on which the RA was received.

This document does not update the way Router Advertisement options are processed. But in addition to the option processing defined in other documents, hosts implementing this specification MUST associate each created or updated object (e.g. address, default route, more specific route, DNS server list) with the PvD associated with the received RA.

While resolving names, executing the default address selection algorithm [RFC6724] or executing the default router selection algorithm ([RFC2461], [RFC4191] and [RFC8028]), hosts MAY consider only the configuration associated with an arbitrary set of PvDs.

For example, a host MAY associate a given process with a specific PvD, or a specific set of PvDs, while associating another process with another PvD. A PvD-aware application might also be able to select, on a per-connection basis, which PvDs should be used for a given connection. In particular, constrained devices such as small battery operated devices (e.g. IoT), or devices with limited CPU or memory resources may purposefully use a single PvD while ignoring some received RAs containing different PvD IDs.

The way an application expresses its desire to use a given PvD, or a set of PvDs, or the way this selection is enforced, is out of the scope of this document. Useful insights about these considerations can be found in [I-D.kline-mif-mpvd-api-reqs].

3.3.1. DHCPv6 configuration association

When a host retrieves configuration elements using DHCPv6, they MUST be associated with the explicit or implicit PvD of the RA received on the same interface, sent from the same LLA, and with the O-flag set [RFC4861]. If no such PvD is found, or whenever multiple different PvDs are found, the host behavior is unspecified.

This process requires hosts to keep track of received RAs, associated PvD IDs, and routers LLA; it also assumes that the router either acts as a DHCPv6 server or relay and uses the same LLA for DHCPv6 and RA traffic (which may not be the case when the router uses VRRP to send its RA).

3.3.2. DHCPv4 configuration association

When a host retrieves configuration elements from DHCPv4, they MUST be associated with the explicit PvD received on the same interface, whose PVD ID Options L-flag is set and, in the case of a non point-to-point link, using the same datalink address. If no such PvD is found, or whenever multiple different PvDs are found, the configuration elements coming from DHCPv4 MUST be associated with an IPv4-only implicit PvD identified by the interface on which the DHCPv4 transaction happened. The case of multiple explicit PvD for an IPv4 interface is undefined.

3.3.3. Interconnection Sharing by the Host

The situation when a node receives RA on one interface (e.g. cellular) and shares this connectivity by also acting as a router by transmitting RA on another interface (e.g. WiFi) is known as 'tethering'. It can be done as ND proxy. The exact behavior is TBD but it is expected that the one or several PvD associated to the shared interface (e.g. cellular) will also be advertised to the clients on the other interface (e.g. WiFi).

4. Provisioning Domain Additional Information

Once a new PvD ID is discovered, it may be used to retrieve additional information about the characteristics of the provided connectivity. This set of information is called PvD Additional Information, and is encoded as a JSON object [RFC7159].

The purpose of this additional set of information is to securely provide additional information to hosts about the connectivity that is provided using a given interface and source address pair. It typically includes data that would be considered too large, or not critical enough, to be provided within an RA option. The information contained in this object MAY be used by the operating system, network libraries, applications, or users, in order to decide which set of PvDs should be used for which connection, as described in Section 3.3.

4.1. Retrieving the PvD Additional Information

When the H-flag of the PvD ID Option is set, hosts MAY attempt to retrieve the PvD Additional Information associated with a given PvD by performing an HTTP over TLS [RFC2818] GET query to https://<PvD-ID>/.well-known/pvd [RFC5785]. Inversely, hosts MUST NOT do so whenever the H-flag is not set.

Note that the DNS name resolution of <PvD-ID> as well as the actual query MUST be performed using the PvD associated with the PvD ID. In other words, the name resolution, source address selection, as well as the next-hop router selection MUST be performed while using exclusively the set of configuration information attached with the PvD, as defined in Section 3.3. In some cases, it may therefore be necessary to wait for an address to be available for use (e.g., once the Duplicate Address Detection or DHCPv6 processes are complete) before initiating the HTTP over TLS query. If the PvD allows for temporary address per [RFC4941], then host SHOULD use a temporary address to fetch the PvD Additional Information and SHOULD deprecate the used temporary address and generate a new temporary address.

If the HTTP status of the answer is greater than or equal to 400 the host MUST abandon and consider that there is no additional PvD information. If the HTTP status of the answer is between 300 and 399, inclusive, it MUST follow the redirection(s). If the HTTP status of the answer is between 200 and 299, inclusive, the host MAY get a file containing a single JSON object. When a JSON object could not be retrieved, an error message SHOULD be logged and/or displayed in a rate-limited fashion.

After retrieval of the PvD Additional Information, hosts MUST watch the PvD ID Sequence field for change. In case a different value than the one in the RA Sequence field is observed, or whenever the validity time included in the PVD Additional Information JSON object is expired, hosts MUST either perform a new query and retrieve a new version of the object, or, failing that, deprecate the object and stop using it.

Hosts retrieving a new PvD Additional Information object MUST check for the presence and validity of the mandatory fields Section 4.3. A retrieved object including an outdated expiration time or missing a mandatory element MUST be ignored. In order to avoid traffic spikes toward the server hosting the PvD Additional Information when an object expires, a host which last retrieved an object at a time A, including a validity time B, SHOULD renew the object at a uniformly random time in the interval [(B-A)/2,A].

The PvD Additional Information object includes a set of IPv6 prefixes (under the key "prefixes") which MUST be checked against all the Prefix Information Options advertised in the RA. If any of the prefixes included in the PIO is not covered by at least one of the listed prefixes, the PvD associated with the tested prefix MUST be considered unsafe and MUST NOT be used. While this does not prevent a malicious network provider, it does complicate some attack scenarios, and may help detecting misconfiguration.

The server providing the JSON files SHOULD also check whether the client address is part of the prefixes listed into the additional information and SHOULD return a 403 response code if there is no match. The server MAY also use the client address to select the right JSON object to be returned.

4.2. Providing the PvD Additional Information

Whenever the H-flag is set in the PvD RA Option, a valid PvD Additional Information object MUST be made available to all hosts receiving the RA by the network operator. In particular, when a captive portal is present, hosts MUST still be allowed to access the object, even before logging into the captive portal.

Routers MAY increment the PVD ID Sequence number in order to inform host that a new PvD Additional Information object is available and should be retrieved.

4.3. PvD Additional Information Format

The PvD Additional Information is a JSON object.

The following array presents the mandatory keys which MUST be included in the object:

A retrieved object which does not include a valid string associated with the "name" key at the root of the object, or a valid date associated with the "expires" key, also at the root of the object, MUST be ignored. In such cases, an error message SHOULD be logged and/or displayed in a rate-limited fashion. If the PIO of the received RA is not included in the "prefixes" key, the retrieved object SHOULD be ignored.

The following table presents some optional keys which MAY be included in the object.

It is worth noting that the JSON format allows for extensions. Whenever an unknown key is encountered, it MUST be ignored along with its associated elements.

4.3.1. Connectivity Characteristics Information

The following set of keys can be used to signal certain characteristics of the connection towards the PvD.

They should reflect characteristics of the overall access technology which is not limited to the link the host is connected to, but rather a combination of the link technology, CPE upstream connectivity, and further quality of service considerations.

4.3.2. Private Extensions

JSON keys starting with "x-" are reserved for private use and can be utilized to provide information that is specific to vendor, user or enterprise. It is RECOMMENDED to use one of the patterns "x-FQDN-KEY" or "x-PEN-KEY" where FQDN is a fully qualified domain name or PEN is a private enterprise number under control of the author of the extension to avoid collisions.

4.3.3. Example

Here are two examples based on the keys defined in this section.

{
  "name": "Foo Wireless",
  "localizedName": "Foo-France Wifi",
  "expires": "2017-07-23T06:00:00Z",
  "prefixes" : ["2001:db8:1::/48", "2001:db8:4::/48"],
  "characteristics": {
   "maxThroughput": { "down":200000, "up": 50000 },
   "minLatency": { "down": 0.1, "up": 1 }
  }
}

{
  "name": "Bar 4G",
  "localizedName": "Bar US 4G",
  "expires": "2017-07-23T06:00:00Z",
  "prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
  "metered": true,
  "characteristics": {
    "maxThroughput": { "down":80000, "up": 20000 }
  }
}

4.4. Detecting misconfiguration and misuse

Although some solutions such as IPsec or SEND [RFC3971] can be used in order to secure the IPv6 Neighbor Discovery Protocol, actual deployments largely rely on link layer or physical layer security mechanisms (e.g. 802.1x [IEEE8021X]) in conjunction with RA Guard [RFC6105].

This specification does not improve the Neighbor Discovery Protocol security model, but extends the purely link-local configuration retrieval mechanisms with HTTP-over-TLS communications and some checks to detect misconfiguration and some misuses.

When a host retrieves the PvD Additional Information, it MUST verify that the HTTPS server certificate is valid and that the Subject Name is equal to the PvD ID expressed as an FQDN. This authentication creates a secure binding between the information provided by the trusted Router Advertisement, and the HTTPS server. But this does not mean the Advertising Router and the PvD server belong to the same entity.

When the "prefixes" key is included in the PvD Additional Information, then host MUST verify that all prefixes in the RA PIO are covered by a prefixes from the PvD Additional Informaion. An adversarial router willing to fake the use of a given explicit PvD, without any access to the actual PvD Additional Information, would need to perform NAT66 in order to circumvent this check.

It is also RECOMMENDED that the HTTPS server checks the source addresses of incoming connections (see Section 4.1). This checks give reasonable assurance that NAT66 was not used and also restrict the information to the valid network users.

5. Security Considerations

It must be noted that the Section 4.4 of this document only provides reasonable assurance against misconfiguration but does not prevent an hostile network access provider to wrong information that could lead applications or hosts to select an hostile PvD. Users should always apply caution when connecting to an unknown network.

6. Privacy Considerations

When a host retrieves via HTTPS the additional information, all nodes on the path (including the HTTPS server) can detect that the node is active.

As it can be expected that the HTTPS server is located in the same management domain as the client (usually, it will be within an enterprise network, WiFi hotspot, or Service Provider network), the network operator as usually other means to also detect the new active node (DHCP, Neighbor Discovery Protocol cache inspection or DNS request logging). In this case, privacy is not worsened by using PvD.

It must also be noted that most operating systems implement a system to detect the presence of a captive portal and also connect to a well-known web site over the Internet, for example to http://captive.example.com/hotspot-detect.html. This detection mechanism is exposing the activity of the detecting node not only within the management domain but also to all nodes outside this domain on the path to the captive.example.com server. As PvD can also be used to detect captive portal, then the PvD actually preserves privacy.

Finally, the fetching of additional information is an option and could be disabled by the host.

7. IANA Considerations

IANA is asked to assign the value TBD from the IPv6 Neighbor Discovery Option Formats registry for the PvD ID Router Advertisement option.

IANA is asked to assign the value "pvd" from the Well-Known URIs registry.

IANA is asked to create and maintain a new registry entitled "Additional Information PvD Keys" containing ASCII strings. The initial content of this registry are given below; future assignements are to be made through Expert Review [BCP36].

8. Acknowledgements

Many thanks to M. Stenberg and S. Barth for their earlier work: [I-D.stenberg-mif-mpvd-dns].

Thanks also to Mikael Abrahamson, Ray Bellis, Lorenzo Colitti, Thierry Danis, Bob Hinden, Tatuya Jinmei, Erik Kline, Ted Lemon, Jen Lenkova, Mark Townsley, James Woodyatt for useful and interesting discussions.

Finally, many thanks to Thierry Danis for his implementation work ([github]), Tom Jones for his integration effort into the Neat project and Rigil Salim for his implementation work.

9. Contributor

Basile Bruneau was a co-author of this document while he was studying at the Polytechnique Paris.

10. References

10.1. Normative references

10.2. Informative references

Appendix A. Changelog

Note to RFC Editors: Remove this section before publication.

A.1. Version 00

Initial version of the draft. Edited by Basile Bruneau + Eric Vyncke and based on Basile's work.

A.2. Version 01

Major rewrite intended to focus on the the retained solution based on corridors, online, and WG discussions. Edited by Pierre Pfister. The following list only includes major changes.

• PvD ID is an FQDN retrieved using a single RA option. This option contains a sequence number for push-based updates, a new H-flag, and a L-flag in order to link the PvD with the IPv4 DHCP server.
• A lifetime is included in the PvD ID option.
• Detailed Hosts and Routers specifications.
• Additional Information is retrieved using HTTP-over-TLS when the PvD ID Option H-flag is set. Retrieving the object is optional.
• The PvD Additional Information object includes a validity date.
• DNS-based approach is removed as well as the DNS-based encoding of the PvD Additional Information.
• Major cut in the list of proposed JSON keys. This document may be extended later if need be.
• Monetary discussion is moved to the appendix.
• Clarification about the 'prefixes' contained in the additional information.
• Clarification about the processing of DHCPv6.

A.3. Version 02

• The FQDN is now encoded with ASCII format (instead of DNS binary) in the RA option.
• The PvD ID option lifetime is removed from the object.
• Use well known URI "https://<PvD-ID>/.well-known/pvd"
• Reference RFC3339 for JSON timestamp format.
• The PvD ID Sequence field has been extended to 16 bits.
• Modified host behavior for DHCPv4 and DHCPv6.
• Removed IKEv2 section.
• Removed mention of RFC7710 Captive Portal option. A new I.D. will be proposed to address the captive portal use case.

A.4. WG Document version 00

• Document has been accepted as INTAREA working group document
• IANA considerations follow RFC8126
• PvD ID FQDN is encoded as per RFC 1035
• PvD ID FQDN is prepended by a one-byte length field
• Marcus Keane added as co-author
• dnsZones key is added back
• draft of a privacy consideration section and added that a temporary address should be used to retrieve the PvD additional information
• per Bob Hinden's request: the document is now aiming at standard track and security considerations have been moved to the main section

Appendix B. Connection monetary cost

NOTE: This section is included as a request for comment on the potential use and syntax.

The billing of a connection can be done in a lot of different ways. The user can have a global traffic threshold per month, after which his throughput is limited, or after which he/she pays each megabyte. He/she can also have an unlimited access to some websites, or an unlimited access during the weekends.

An option is to split the bill in elementary billings, which have conditions (a start date, an end date, a destination IP address...). The global billing is an ordered list of elementary billings. To know the cost of a transmission, the host goes through the list, and the first elementary billing whose the conditions are fulfilled gives the cost. If no elementary billing conditions match the request, the host MUST make no assumption about the cost.

B.1. Conditions

Here are the potential conditions for an elementary billing. All conditions MUST be fulfill.

B.2. Price

Here are the different possibilities for the cost of an elementary billing. A missing key means "all/unlimited/unrestricted". If the elementary billing selected has a trafficRemaining of 0 kb, then it means that the user has no access to the network. Actually, if the last elementary billing has a trafficRemaining parameter, it means that when the user will reach the threshold, he/she will not have access to the network anymore.

B.3. Examples

Example for a user with 20 GB per month for 40 EUR, then reach a threshold, and with unlimited data during weekends and to example.com:

[
  {
    "domains": ["example.com"]
  },
  {
    "prefixes4": ["78.40.123.182/32","78.40.123.183/32"]
  },
  {
    "beginDate": "2016-07-16T00:00:00Z",
    "endDate": "2016-07-17T23:59:59Z",
  },
  {
    "beginDate": "2016-06-20T00:00:00Z",
    "endDate": "2016-07-19T23:59:59Z",
    "trafficRemaining": 12000000
  },
  {
    "throughputMax": 100000
  }
]
            

If the host tries to download data from example.com, the conditions of the first elementary billing are fulfilled, so the host takes this elementary billing, finds no cost indication in it and so deduces that it is totally free. If the host tries to exchange data with foobar.com and the date is 2016-07-14T19:00:00Z, the conditions of the first, second and third elementary billing are not fulfilled. But the conditions of the fourth are. So the host takes this elementary billing and sees that there is a threshold, 12 GB are remaining.

Another example for a user abroad, who has 3 GB per year abroad, and then pay each MB:

[
  {
    "beginDate": "2016-02-10T00:00:00Z",
    "endDate": "2017-02-09T23:59:59Z",
    "trafficRemaining": 3000000
  },
  {
    "pricePerGb": 30,
    "currency": "EUR"
  }
]
            

Authors' Addresses