| intarea | P. Pfister |
| Internet-Draft | E. Vyncke, Ed. |
| Intended status: Standards Track | Cisco |
| Expires: August 13, 2018 | T. Pauly |
| D. Schinazi | |
| Apple | |
| February 9, 2018 |
Discovering Provisioning Domain Names and Data
draft-ietf-intarea-provisioning-domains-01
An increasing number of hosts access the Internet via multiple interfaces or, in IPv6 multi-homed networks, via multiple IPv6 prefix configurations.
This document describes a way for hosts to identify such means, called Provisioning Domains (PvDs), with Fully Qualified Domain Names (FQDN). Those identifiers are advertised in a new Router Advertisement (RA) option and, when present, are associated with the set of information included within the RA.
Based on this FQDN, hosts can retrieve additional information about their network access characteristics via an HTTP over TLS query. This allows applications to select which Provisioning Domains to use as well as to provide configuration parameters to the transport layer and above.
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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 August 13, 2018.
Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.
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It has become very common in modern networks for hosts to access the internet 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 document specifies a way to identify PvDs with Fully Qualified Domain Names (FQDN), called PvD IDs. Those identifiers are advertised in a new Router Advertisement (RA) [RFC4861] option called the PvD ID Router Advertisement option which, when present, associates the PvD ID with all the information present in the Router Advertisement as well as any configuration object, such as addresses, deriving from it. The PVD ID Router Advertisement option may also contain a set of other RA options. Since such options are only considered by hosts implementing this specification, network operators may configure hosts that are 'PvD-aware' with PvDs that are ignored by other hosts.
Since PvD IDs are used to identify different ways to access the internet, multiple PvDs (with different PvD IDs) could be provisioned on a single host interface. Similarly, the same PvD ID could be used on different interfaces of a host in order to inform that those PvDs ultimately provide identical services.
This document also introduces a way for hosts to retrieve additional information related to a specific PvD by means of an HTTP over TLS query using an URI derived from the PvD ID. The retrieved JSON object contains additional information that would typically be considered unfit, or too large, to be directly included in the Router Advertisement, but might be considered useful to the applications, or even sometimes users, when choosing which PvD and transport should be used.
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:
Explicit PvDs are 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 naming collisions. The same PvD ID MAY be used in several access networks when they ultimately provide identical services (e.g., in all home networks subscribed to the same service).
This document introduces a Router Advertisement (RA) option called PvD ID Router Advertisement option. It is used to convey the FQDN identifying a given PvD (see Figure 1), bind the PvD ID with configuration information received over DHCPv4 (see Section 3.3.2), enable the use of HTTP over TLS to retrieve the PvD Additional Information JSON object (see Section 4), as well as contain any other RA options which would otherwise be valid in the RA.
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|A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
... PvD ID FQDN ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...
... Router Advertisement message header ...
... (Only present when A-flag is set) ...
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: PvD ID Router Advertisements Option format
Here is an example of a PvD ID option with example.org as the PvD ID FQDN and including a RDNSS and prefix information options:
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: 254 | Length: 12 |0|0|0| Reserved | +---------------+-------------------------------+---------------+ | Sequence Number | 7 | e | +---------------+-----------------------------------------------+ | m | a | m | p | +---------------------------------------------------------------+ | l | e | 3 | o | +---------------------------------------------------------------+ | r | g | 0 | 0 (padding) | +---------------------------------------------------------------+ | 0 (padding) | 0 (padding) | 0 (padding) | 0 (padding) | +---------------+---------------+---------------+---------------+ | RDNSS option (RFC 6106) length: 5 ... ... ... ... | +---------------------------------------------------------------+ | Prefix Information Option (RFC 4861) length: 4 ... ... | ... | +---------------------------------------------------------------+
A router MAY send RAs containing at most one PvD ID RA option, but MUST NOT include more than one PvD ID RA option in each RA. In particular, the PvD ID RA option MUST NOT contain further PvD ID RA options.
The PvD ID Option MAY contain zero, one, or more RA options which would otherwise be valid as part of the same RA. Such options are processed by PvD-aware hosts, while ignored by others.
In order to provide multiple different PvDs, a router MUST send multiple RAs. Different explicit PvDs MAY be advertised with RAs using the same IPv6 source address; but different implicit PvDs, advertised with different RAs, MUST use different link local addresses.
Whenever an RA, for a single PvD, would need to be sent via multiple packets, the PvD ID RA option header (i.e., all fields except the 'Options' field) MUST be repeated in all the transmitted RAs. But the options within the 'Options' field, MAY be transmitted only once, included in one of the transmitted PvD ID RA options.
Hosts MUST associate received RAs and included configuration information (e.g., Router Valid Lifetime, Prefix Information [RFC4861], Recursive DNS Server [RFC8106], Routing Information [RFC4191] options) with the explicit PvD identified by the first PvD ID Option present in the received RA, if any, or with the implicit PvD identified by the host interface and the source address of the received RA otherwise.
In case multiple PvD ID options are found in a given RA, hosts MUST ignore all but the first PvD ID option.
Similarly, hosts MUST associate all network configuration objects (e.g., default routers, addresses, more specific routes, DNS Recursive Resolvers) with the PvD associated with the RA which last updated the object. For example, addresses that are generated using a received Prefix Information option (PIO) are associated with the PvD of the last received RA which included the given PIO.
PvD IDs MUST be compared in a case-insensitive manner (i.e., A=a), assuming ASCII with zero parity while non-alphabetic codes must match exactly (see also Section 3.1 of [RFC1035]). For example, pvd.example.com or PvD.Example.coM would refer to the same PvD.
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. 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].
When a host retrieves configuration elements using DHCPv6 (e.g., addresses or DNS recursive resolvers), 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 or M-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).
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 the implicit PvD identified by the interface on which the DHCPv4 transaction happened. The case of multiple explicit PvD for an IPv4 interface is undefined.
The situation when a node receives an 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).
Additional information about the network characteristics can be retrieved based on the PvD ID. 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 applications 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.
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 the PvD ID, the PKI checks as well as the actual query MUST be performed using the considered PvD. In other words, the name resolution, PKI checks, 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 hosts SHOULD use a temporary address to fetch the PvD Additional Information and SHOULD deprecate the used temporary address and generate a new temporary address afterward.
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 keep track of the Sequence Number value received in subsequent RAs including the same PvD ID. In case the new value is greater than the value that was observed when the PvD Additional Information object was retrieved (using serial number arithmetic comparisons [RFC1982]), 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 the additional information provided in the JSON object.
Hosts retrieving a new PvD Additional Information object MUST check for the presence and validity of the mandatory fields specified in Section 4.3. A retrieved object including an expiration time that is already past or missing a mandatory element MUST be ignored. In order to avoid synchronized queries 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.
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 perform DNS, PKI and HTTP over TLS operations related to the retrieval of 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.
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 PvD Additional Information is a JSON object.
The following table presents the mandatory keys which MUST be included in the object:
| JSON key | Description | Type | Example |
|---|---|---|---|
| name | Human-readable service name | UTF-8 string [RFC3629] | "Awesome Wifi" |
| expires | Date after which this object is not valid | [RFC3339] | "2017-07-23T06:00:00Z" |
| prefixes | Array of IPv6 prefixes valid for this PVD | Array of strings | ["2001:db8:1::/48", "2001:db8:4::/48"] |
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 covered by at least one of the "prefixes" key, the retrieved object SHOULD be ignored.
The following table presents some optional keys which MAY be included in the object.
| JSON key | Description | Type | Example |
|---|---|---|---|
| localizedName | Localized user-visible service name, language can be selected based on the HTTP Accept-Language header in the request. | UTF-8 string | "Wifi Génial" |
| dnsZones | DNS zones searchable and accessible | array of DNS zones | ["example.com","sub.example.org"] |
| noInternet | No Internet, set when the PvD only provides restricted access to a set of services | boolean | true |
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.
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.
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"],
}
{
"name": "Bar 4G",
"localizedName": "Bar US 4G",
"expires": "2017-07-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
}
When a host retrieves the PvD Additional Information, it MUST verify that the TLS server certificate is valid for the performed request (e.g., 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.
Hosts MUST verify that all prefixes in the RA PIO are covered by a prefix from the PvD Additional Information. 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 check give reasonable assurance that neither NPTv6 [RFC6296] nor NAT66 were used and restricts the information to the valid network users.
This section describes some use cases of PvD. For sake of simplicity, the RA messages will not be described in the usual ASCII art but rather in an indented list. For example, a RA message containing some options and a PvD ID option that also contains other options will be described as:
It is expected that for some years, networks will have a mix of PvD-aware hosts and PvD-ignorant hosts. If there is a need to give specific information to PvD-aware hosts only, then it is recommended to send TWO RA messages: one for each class of hosts. For example, here is the RA for PvD-ignorant hosts:
And here is a RA example for PvD-aware hosts:
In the above example, PvD-ignorant hosts will only use the first RA sent from their default router and using the 2001:db8:cafe::/64 prefix. PvD-aware hosts will autonomously configure addresses from both PIOs, but will only use the source address in 2001:db8:f00d::/64 to communicate past the first hop router since only the router sending the second RA will be used as default router; similarly, they will use the DNS server 2001:db8:f00d::53 when communicating with this adress.
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 trust relationship between the host and the default routers with HTTP over TLS communications which servers are authenticated as rightful owners of the FQDN received within the trusted PvD ID RA option.
It must be noted that 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.
Retrieval of the PvD Additional Information over HTTPS requires early communications between the connecting host and a server which may be located further than the first hop router. Although this server is likely to be located within the same administrative domain as the default router, this property can't be ensured. Therefore, hosts willing to retrieve the PvD Additional Information before using it without leaking identity information, SHOULD make use of an IPv6 Privacy Address and SHOULD NOT include any privacy sensitive data, such as User Agent header or HTTP cookie, while performing the HTTP over TLS query.
From a privacy perspective, retrieving the PvD Additional Information is not different from establishing a first connexion to a remote server, or even performing a single DNS lookup. For example, most operating systems already perform early queries to well known web sites, such as http://captive.example.com/hotspot-detect.html, in order to detect the presence of a captive portal.
There may be some cases where hosts, for privacy reasons, should refrain from accessing servers that are located outside a certain network boundary. In practice, this could be implemented as a whitelist of 'trusted' FQDNs and/or IP prefixes that the host is allowed to communicate with. In such scenarios, the host SHOULD check that the provided PvD ID, as well as the IP address that it resolves into, are part of the allowed whitelist.
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 in Section 4.3; future assignments are to be made through Expert Review [BCP36].
Finally, IANA is asked to create and maintain a new registry entitled "PvD ID Router Advertisement option Flags" reserving bit positions from 0 to 15 to be used in the PvD ID Router Advertisement option bitmask. Bit position 0, 1 and 2 are reserved by this document (as specified in Figure 1). Future assignments require a Standard Track RFC document.
Many thanks to M. Stenberg and S. Barth for their earlier work: [I-D.stenberg-mif-mpvd-dns], as well as to Basile Bruneau who was author of an early version of this document.
Thanks also to Marcus Keane, Mikael Abrahamson, Ray Bellis, Lorenzo Colitti, Bob Hinden, Tatuya Jinmei, Erik Kline, Ted Lemon, Jen Lenkova, Mark Townsley and James Woodyatt for useful and interesting discussions.
Finally, special thanks to Thierry Danis and Wenqin Shao for their valuable inputs and implementation efforts ([github]), Tom Jones for his integration effort into the NEAT project and Rigil Salim for his implementation work.
| [RFC1035] | Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987. |
| [RFC1982] | Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, DOI 10.17487/RFC1982, August 1996. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC2461] | Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, DOI 10.17487/RFC2461, December 1998. |
| [RFC2818] | Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000. |
| [RFC3629] | Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003. |
| [RFC4861] | Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007. |
| [RFC7159] | Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014. |
| [RFC8126] | Cotton, M., Leiba, B. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017. |
Note to RFC Editors: Remove this section before publication.
Initial version of the draft. Edited by Basile Bruneau + Eric Vyncke and based on Basile's work.
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.