Location Information Server (LIS) Discovery Using IP Addresses and Reverse DNS
RFC 7216
| Document | Type | RFC - Proposed Standard (April 2014; No errata) | |
|---|---|---|---|
| Authors | Martin Thomson , Ray Bellis | ||
| Last updated | 2018-12-20 | ||
| Replaces | draft-thomson-geopriv-res-gw-lis-discovery | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | WG Document | |
| Document shepherd | Alissa Cooper | ||
| Shepherd write-up | Show (last changed 2013-07-17) | ||
| IESG | IESG state | RFC 7216 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Richard Barnes | ||
| IESG note | Alissa Cooper (acooper@cdt.org) is the document shepherd. | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IANA Actions | ||
Internet Engineering Task Force (IETF) M. Thomson
Request for Comments: 7216 Mozilla
Category: Standards Track R. Bellis
ISSN: 2070-1721 Nominet UK
April 2014
Location Information Server (LIS) Discovery
Using IP Addresses and Reverse DNS
Abstract
The residential gateway is a device that has become an integral part
of home networking equipment. Discovering a Location Information
Server (LIS) is a necessary part of acquiring location information
for location-based services. However, discovering a LIS when a
residential gateway is present poses a configuration challenge,
requiring a method that is able to work around the obstacle presented
by the gateway.
This document describes a solution to this problem. The solution
provides alternative domain names as input to the LIS discovery
process based on the network addresses assigned to a Device.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7216.
Thomson & Bellis Standards Track [Page 1]
RFC 7216 LIS Discovery by IP April 2014
Copyright Notice
Copyright (c) 2014 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
(http://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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Residential Gateway . . . . . . . . . . . . . . . . . . . 6
3.2. Security Features of Residential Gateways . . . . . . . . 7
4. IP-based DNS Solution . . . . . . . . . . . . . . . . . . . . 7
4.1. Identification of IP Addresses . . . . . . . . . . . . . 8
4.2. Domain Name Selection . . . . . . . . . . . . . . . . . . 9
4.3. Shortened DNS Names . . . . . . . . . . . . . . . . . . . 9
4.4. When To Use the Reverse DNS Method . . . . . . . . . . . 10
4.5. Private Address Spaces . . . . . . . . . . . . . . . . . 10
4.6. Necessary Assumptions and Restrictions . . . . . . . . . 11
4.7. Failure Modes . . . . . . . . . . . . . . . . . . . . . . 12
4.8. Deployment Considerations . . . . . . . . . . . . . . . . 12
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IAB Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Thomson & Bellis Standards Track [Page 2]
RFC 7216 LIS Discovery by IP April 2014
1. Introduction
A Location Information Server (LIS) is a service provided by an
access network. The LIS uses knowledge of the access network
topology and other information to generate location information for
Devices. Devices within an access network are able to acquire
location information from a LIS.
The relationship between a Device and an access network might be
transient. Configuration of the correct LIS at the Device ensures
that accurate location information is available. Without location
information, some network services are not available.
The configuration of a LIS IP address on a Device requires some
automated process. This is particularly relevant when one considers
that Devices might move between different access networks served by
different LISs. LIS Discovery [RFC5986] describes a method that
employs the Dynamic Host Configuration Protocol (DHCPv4 [RFC2131],
DHCPv6 [RFC3315]) as input to U-NAPTR [RFC4848] discovery.
A residential gateway, or home router, provides a range of networking
functions for Devices within the network it serves. Unfortunately,
in most cases these functions effectively prevent the successful use
of DHCP for LIS discovery.
One drawback with DHCP is that universal deployment of a new option
takes a considerable amount of time. Often, networking equipment
needs to be updated in order to support the new option. Of
particular concern are the millions of residential gateway devices
used to provide Internet access to homes and businesses. While
[RFC5986] describes functions that can be provided by residential
gateways to support LIS discovery, gateways built before the
publication of this specification are not expected (and are likely
not able) to provide these functions.
This document explores the problem of configuring Devices with a LIS
address when a residential gateway is interposed between the Device
and access network. Section 3 defines the problem, and Section 4
describes a method for determining a domain name that can be used for
discovery of the LIS.
In some cases, the solution described in this document is based on a
UNilateral Self-Address Fixing (UNSAF) [RFC3424] method. For those
cases, this solution is considered transitional until such time as
the recommendations for residential gateways in [RFC5986] are more
widely deployed. Considerations relating to UNSAF applications are
described in Section 7.
Thomson & Bellis Standards Track [Page 3]
RFC 7216 LIS Discovery by IP April 2014
2. Conventions Used in This Document
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 [RFC2119].
This document uses terminology established in [RFC6280] and
[RFC5012]. The terms "Device" and "LIS" are capitalized throughout
when they are used to identify the roles defined in [RFC6280].
3. Problem Statement
Figure 1 shows a simplified network topology for fixed wire-line
Internet access. This arrangement is typical when wired Internet
access is provided. The diagram shows two network segments: the
access network provided by an Internet service provider (ISP), and
the residential network served by the residential gateway.
There are a number of variations on this arrangement, as documented
in Section 3.1 of [RFC5687]. In each of these variations, the goal
of LIS discovery is to identify the LIS in the access network.
Thomson & Bellis Standards Track [Page 4]
RFC 7216 LIS Discovery by IP April 2014
________
(/ \)
(( Internet ))
(\________/)
|
|
.- - -|- - - - - - - - - - - -.
( | )
( +--------+ +-------+ )
Access ( | Access |. . . .| LIS | )
Network ( | Node | | | )
(ISP) ( +--------+ +-------+ )
( \ \ )
`- - - -\- - - - - - - -\- - -'
\ \
\ |
.- - - - -\- - - - - - - + -.
( \ | )
( +-------------+ : )
( | Residential | | )
Residential ( | Gateway | : )
Network ( +-------------+ | )
( / \ / )
( / \ / )
( +--------+ +--------+ )
( | Device | | Device | )
( +--------+ +--------+ )
( )
`- - - - - - - - - - - - - -'
Figure 1: Simplified Network Topology
A particularly important characteristic of this arrangement is the
relatively small geographical area served by the residential gateway.
Given a small enough area, it is reasonable to delegate the
responsibility for providing Devices within the residential network
with location information to the ISP. The ISP is able to provide
location information that identifies the residence, which should be
adequate for a wide range of purposes.
A residential network that covers a larger geographical area might
require a dedicated LIS, a case that is outside the scope of this
document.
Thomson & Bellis Standards Track [Page 5]
RFC 7216 LIS Discovery by IP April 2014
The goal of LIS discovery is to identify a LIS that is able to
provide the Device with accurate location information. In the
network topology described, this means identifying the LIS in the
access network. The residential gateway is a major obstacle in
achieving this goal.
3.1. Residential Gateway
A residential gateway can encompass several different functions
including: modem, Ethernet switch, wireless access point, router,
network address translation (NAT), DHCP server, DNS relay, and
firewall. Of the common functions provided, the NAT function of a
residential gateway has the greatest impact on LIS discovery.
An ISP is typically parsimonious about their IP address allocations;
each customer is allocated a limited number of IP addresses.
Therefore, NAT is an extremely common function of gateways. NAT
enables the use of multiple Devices within the residential network.
However, NAT also means that Devices within the residence are not
configured by the ISP directly.
When it comes to discovering a LIS, the fact that Devices are not
configured by the ISP causes a significant problem. Configuration is
the ideal method of conveying the information necessary for
discovery. Devices attached to residential gateways are usually
given a generic configuration that includes no information about the
ISP network. For instance, DNS configuration typically points to a
DNS relay on the gateway device. This approach ensures that the
local network served by the gateway is able to operate without a
connection to the ISP, but it also means that Devices are effectively
ignorant of the ISP network.
[RFC5986] describes several methods that can be applied by a
residential gateway to assist Devices in acquiring location
information. For instance, the residential gateway could forward LIS
address information to hosts within the network it serves.
Unfortunately, such an active involvement in the discovery process
only works for new residential gateway devices that implement those
recommendations.
Where residential gateways already exist, direct involvement of the
gateway in LIS discovery requires that the residential gateway be
updated or replaced. The cost of replacement is difficult to justify
to the owner of the gateway, especially when it is considered that
the gateway still fills its primary function: Internet access.
Furthermore, updating the software in such devices is not feasible in
Thomson & Bellis Standards Track [Page 6]
RFC 7216 LIS Discovery by IP April 2014
many cases. Even if software updates were made available, many
residential gateways cannot be updated remotely, inevitably leading
to some proportion that is not updated.
This document therefore describes a method that can be used by
Devices to discover their LIS without any assistance from the
network.
3.2. Security Features of Residential Gateways
A network firewall function is often provided by residential gateways
as a security measure. Security features like intrusion detection
systems help protect users from attacks. Amongst these protections
is a port filter that prevents both inbound and outbound traffic on
certain TCP and UDP ports. Therefore, any solution needs to consider
the likelihood of traffic being blocked.
4. IP-based DNS Solution
LIS discovery [RFC5986] uses a DNS-based Dynamic Delegation Discovery
Service (DDDS) system as the basis of discovery. Input to this
process is a domain name. Use of DHCP for acquiring the domain name
is specified, but alternative methods of acquisition are permitted.
This document specifies a means for a Device to discover several
alternative domain names that can be used as input to the DDDS
process. These domain names are based on the IP address of the
Device. Specifically, the domain names are a portion of the reverse
DNS trees -- either the ".in-addr.arpa." or ".ip6.arpa." tree.
The goal of this process is to make a small number of DDDS queries in
order to find a LIS. After LIS discovery using the DHCP-based
process in [RFC5986] has failed, a Device can:
1. Collect a set of IP addresses that refer to the Device
(Section 4.1).
2. Convert each IP address into DNS names in the "in-addr.arpa." or
"ip6.arpa." tree (Section 4.2).
3. Perform the DDDS process for LIS discovery on those DNS names
([RFC5986]).
4. Shorten the DNS names by some number of labels and repeat the
DDDS process (Section 4.3).
Thomson & Bellis Standards Track [Page 7]
RFC 7216 LIS Discovery by IP April 2014
A Device might be reachable at one of a number of IP addresses. In
the process described, a Device first identifies each IP address from
which it is potentially reachable. From each of these addresses, the
Device then selects up to three domain names for use in discovery.
These domain names are then used as input to the DDDS process.
4.1. Identification of IP Addresses
A Device identifies a set of potential IP addresses that currently
result in packets being routed to it. These are ordered by
proximity, with those addresses that are used in adjacent network
segments being favored over those used in public or remote networks.
The first addresses in the set are those that are assigned to local
network interfaces.
A Device can use the Session Traversal Utilities for NAT (STUN)
[RFC5389] mechanism to determine its public, reflexive transport
address. The host uses the "Binding Request" message and the
resulting "XOR-MAPPED-ADDRESS" parameter that is returned in the
response.
Alternative methods for determining other IP addresses MAY be used by
the Device. If enabled, the Port Control Protocol (PCP) [RFC6887],
Universal Plug and Play (UPnP) [UPnP-IGD-WANIPConnection1], and NAT
Port Mapping Protocol (NAT-PMP) [RFC6886] are each able to provide
the external address of a residential gateway device. These, as well
as proprietary methods for determining other addresses, might be
available. Because there is no assurance that these methods will be
supported by any access network, these methods are not mandated.
Note also that in some cases, methods that rely on the view of the
network from the residential gateway device could reveal an address
in a private address range (see Section 4.6).
In many instances, the IP address produced might be from a private
address range. For instance, the address on a local network
interface could be from a private range allocated by the residential
gateway. In other cases, methods that rely on the view of the
network (UPnP, NAT-PMP) from the residential gateway device could
reveal an address in a private address range if the access network
also uses NAT. For a private IP address, the derived domain name is
only usable where the employed DNS server contains data for the
corresponding private IP address range.
Thomson & Bellis Standards Track [Page 8]
RFC 7216 LIS Discovery by IP April 2014
4.2. Domain Name Selection
The domain name selected for each resulting IP address is the name
that would be used for a reverse DNS lookup. The domain name derived
from an IP version 4 address is in the ".in-addr.arpa." tree and
follows the construction rules in Section 3.5 of [RFC1035]. The
domain name derived from an IP version 6 address is in the
".ip6.arpa." tree and follows the construction rules in Section 2.5
of [RFC3596].
4.3. Shortened DNS Names
Additional domain names are added to allow for a single DNS record to
cover a larger set of addresses. If the search on the domain derived
from the full IP address does not produce a NAPTR record with the
desired service tag (e.g., "LIS:HELD"), a similar search is repeated
based on a shorter domain name, using a part of the IP address:
o For IP version 4, the resulting domain name SHOULD be shortened
successively by one and two labels, and the query repeated. This
corresponds to a search on a /24 or /16 network prefix. This
allows for fewer DNS records in the case where a single access
network covering an entire /24 or /16 network is served by the
same LIS.
o For IP version 6, the resulting domain SHOULD be shortened
successively by 16, 18, 20, and 24 labels, and the query repeated.
This corresponds to a search on a /64, /56, /48, or /32 network
prefix.
This set of labels is intended to provide network operators with a
degree of flexibility in where LIS discovery records can be placed
without significantly increasing the number of DNS names that are
searched. This does not attach any other significance to these
specific zone cuts or create a classful addressing hierarchy based on
the reverse DNS tree.
For example, the IPv4 address "192.0.2.75" could result in queries
to:
o 75.2.0.192.in-addr.arpa.
o 2.0.192.in-addr.arpa.
o 0.192.in-addr.arpa.
Thomson & Bellis Standards Track [Page 9]
RFC 7216 LIS Discovery by IP April 2014
Similarly, the IPv6 address "2001:DB8::28e4:3a93:4429:dfb5" could
result in queries to:
o 5.b.f.d.9.2.4.4.3.9.a.3.4.e.8.2.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2
.ip6.arpa.
o 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
o 0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
o 0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
o 8.b.d.0.1.0.0.2.ip6.arpa.
The limited number of labels by which each name is shortened is
intended to limit the number of DNS queries performed by Devices. If
no LIS is discovered by this method, the result will be that no more
than five U-NAPTR resolutions are invoked for each IP address.
4.4. When To Use the Reverse DNS Method
The DHCP method described in [RFC5986] MUST be attempted on all local
network interfaces before attempting this method. This method is
employed either because DHCP is unavailable, when the DHCP server
does not provide a value for the access network domain name option,
or because a request to the resulting LIS results in a HELD
"notLocatable" error or equivalent.
4.5. Private Address Spaces
Addresses from a private-use address space can be used as input to
this method. In many cases, this applies to addresses defined in
[RFC1918], though other address ranges could have limited
reachability where this advice also applies. This is only possible
if a DNS server with a view of the same address space is used.
Public DNS servers cannot provide useful records for private
addresses.
Using an address from a private space in discovery can provide a more
specific answer if the DNS server has records for that space.
Figure 2 shows a network configuration where addresses from an ISP
network could better indicate the correct LIS. Records in DNS B can
be provided for the 10.0.0.0/8 range, potentially dividing that range
so that a more local LIS can be selected.
Thomson & Bellis Standards Track [Page 10]
RFC 7216 LIS Discovery by IP April 2014
_____ ________
( DNS ).....(/ \) Public
(__A__) (( Internet )) Address
(\________/) Space
|
[NAT]
_____ _____|_____
( DNS )....(/ \) Private
(__B__) (( ISP Network )) Address Space
(\___________/) (e.g., 10.0.0.0/8)
|
[Gateway]
____|____
(/ \) Private
(( Residence )) Address Space
(\_________/) (e.g., 192.168.0.0/16)
Figure 2: Address Space Example
The goal of automatic DNS configuration is usually to select a local
DNS, which suits configurations like the one shown. However, use of
public DNS or STUN servers means that a public IP address is likely
to be found. For STUN in particular, selecting a public server
minimizes the need for reconfiguration when a Device moves. Adding
records for the public address space used by an access network
ensures that the discovery process succeeds when a public address is
used.
4.6. Necessary Assumptions and Restrictions
When used by a Device for LIS discovery, this is an UNSAF application
and is subject to the limitations described in Section 7.
It is not necessary that the IP address used is unique to the Device,
only that the address can be somehow related to the Device or the
access network that serves the Device. This allows a degree of
flexibility in determining this value, although security
considerations (Section 6) might require that the address be verified
to limit the chance of falsification.
This solution assumes that the public, reflexive transport address
used by a Device is in some way controlled by the access network
provider or some other related party. This implies that the
corresponding ".in-addr.arpa." or ".ip6.arpa." record can be updated
by that entity to include a useful value for the LIS address.
Thomson & Bellis Standards Track [Page 11]
RFC 7216 LIS Discovery by IP April 2014
4.7. Failure Modes
Successful use of private addresses relies on a DNS server that has
records for the address space that is used. Using a public IP
address increases the likelihood of this. This document relies on
STUN to provide the Device with a public, reflexive transport
address. Configuration of a STUN server is necessary to ensure that
this is successful.
In cases where a virtual private network (VPN) or other tunnel is
used, the entity providing a public IP address might not be able to
provide the Device with location information. It is assumed that
this entity is able to identify this problem and indicate this to the
Device (using the "notLocatable" HELD error or similar). This
problem is described in more detail in [RFC5985].
4.8. Deployment Considerations
An access network provider SHOULD provide NAPTR records for each
public IP address that is used for Devices within the access network.
Any DNS server internal to a NAT SHOULD also include records for the
private address range. These records might only be provided to
clients making requests from the private address range. Doing so
allows clients within the private address range to discover a LIS
based on their IP address prior to any address translation. In
geographically distributed networks that use a private address range,
this enables the use of a different LIS for different locations,
based on the IP address range used at each location. Use of a
public, translated IP address for the network can still work, but it
might result in a suboptimal LIS selection.
A network that operates network address translation SHOULD provide
NAPTR records that reference a LIS endpoint with a public address.
This requires the reservation of an IP address and port for the LIS.
To ensure requests toward the LIS from within the private address
space do not traverse the NAT and have source addresses mapped by the
NAT, networks can provide a direct route to the LIS. Clients that
perform discovery based on public DNS or STUN servers are thereby
easier to trace based on source address information.
NAPTR records can be provided for individual IP addresses. To limit
the proliferation of identical records, a single record can be placed
at higher nodes of the tree (corresponding to /24 and /16 for IPv4;
/64, /56, /48, and /32 for IPv6). A record at a higher point in the
tree (those with a shorter prefix) applies to all addresses lower in
Thomson & Bellis Standards Track [Page 12]
RFC 7216 LIS Discovery by IP April 2014
the tree (those with a longer prefix); records at the lower point
override those at higher points, thus allowing for exceptions to be
specified.
5. Privacy Considerations
As with all uses of geolocation information, it is very important
that measures be taken to ensure that location information is not
provided to unauthorized parties. The mechanism defined in this
document is focused on the case where a device is learning its own
location so that it can provide that location information to
applications. We assume that the device learning its own location is
not a privacy risk. There are then two remaining privacy risks: the
use of geolocation by applications, and the abuse of the location
configuration protocol.
The privacy considerations around the use of geolocation by
applications vary considerably by application context. A framework
for location privacy in applications is provided in [RFC6280].
The mechanism specified in this document allows a device to discover
its local LIS, from which it then acquires its location using a
Location Configuration Protocol (LCP) [RFC5687]. If an unauthorized
third party can spoof the LCP to obtain a target's location
information, then the mechanism in this document could allow them to
discover the proper server to attack for a given IP address. Thus,
it is important that a LIS meet the security requirements of the LCP
it implements. For HELD, these requirements are laid out in
Section 9 of [RFC5985].
A Device that discovers a LIS using the methods in this document MUST
NOT provide that LIS with additional information that might reveal
its position, such as the location measurements described in
[RFC7105], unless it has a secondary method for determining the
authenticity of the LIS, such as a white list.
6. Security Considerations
The security considerations described in [RFC5986] apply to the
discovery process as a whole. The primary security concern is with
the potential for an attacker to impersonate a LIS.
The added ability for a third party to discover the identity of a LIS
does not add any concerns, since the identity of a LIS is considered
public information.
Thomson & Bellis Standards Track [Page 13]
RFC 7216 LIS Discovery by IP April 2014
In addition to existing considerations, this document introduces
further security considerations relating to the identification of the
IP address. It is possible that an attacker could attempt to provide
a falsified IP address in an attempt to subvert the rest of the
process.
[RFC5389] describes attacks where an attacker is able to ensure that
a Device receives a falsified reflexive address. An on-path attacker
might be able to ensure that a falsified address is provided to the
Device. Even though STUN messages are protected by a STUN MESSAGE-
INTEGRITY attribute, which is an HMAC that uses a shared secret, an
on-path attacker can capture and modify packets, altering source and
destination addresses to provide falsified addresses.
This attack could result in an effective means of denial of service,
or a means to provide a deliberately misleading service. Notably,
any LIS that is identified based on a falsified IP address could
still be a valid LIS for the given IP address, just not one that is
useful for providing the Device with location information. In this
case, the LIS provides a HELD "notLocatable" error or an equivalent.
If the falsified IP address is under the control of the attacker, it
is possible that misleading (but verifiable) DNS records could
indicate a malicious LIS that provides false location information.
In all cases of falsification, the best remedy is to perform some
form of independent verification of the result. No specific
mechanism is currently available to prevent attacks based on
falsification of reflexive addresses; it is suggested that Devices
attempt to independently verify that the reflexive transport address
provided is accurate. An independent, trusted source of location
information could aid in verification, even if the trusted source is
unable to provide information with the same degree of accuracy as the
discovered LIS.
Use of private address space effectively prevents use of the usual
set of trust anchors for DNSSEC. Only a DNS server that is able to
see the same private address space can provide useful records. A
Device that relies on DNS records in the private address space
portion of the ".in-addr.arpa." or ".ip6.arpa." trees MUST either use
an alternative trust anchor for these records or rely on other means
of ensuring the veracity of the DNS records.
DNS queries that are not blocked as [RFC6303] demands, or directed to
servers outside the network, can cause the addresses that are in use
within the network to be exposed outside of the network. For
resolvers within the network, implementing [RFC6303] avoids this
issue; otherwise, the problem cannot be avoided without blocking DNS
queries to external servers.
Thomson & Bellis Standards Track [Page 14]
RFC 7216 LIS Discovery by IP April 2014
7. IAB Considerations
The IAB has studied the problem of Unilateral Self-Address Fixing
(UNSAF) [RFC3424], which is the general process by which a client
attempts to determine its address in another realm on the other side
of a NAT through a collaborative protocol reflection mechanism, such
as STUN.
This section only applies to the use of this method of LIS discovery
by Devices and does not apply to its use for third-party LIS
discovery.
The IAB requires that protocol specifications that define UNSAF
mechanisms document a set of considerations.
1. Precise definition of a specific, limited-scope problem that is
to be solved with the UNSAF proposal.
Section 3 describes the limited scope of the problem addressed in
this document.
2. Description of an exit strategy/transition plan.
[RFC5986] describes behavior that residential gateways require in
order for this short-term solution to be rendered unnecessary.
When implementations of the recommendations in LIS discovery are
widely available, this UNSAF mechanism can be made obsolete.
3. Discussion of specific issues that may render systems more
"brittle".
A description of the necessary assumptions and limitations of
this solution are included in Section 4.6.
Use of STUN for discovery of a reflexive transport address is
inherently brittle in the presence of multiple NATs or address
realms. In particular, brittleness is added by the requirement
of using a DNS server that is able to view the address realm that
contains the IP address in question. If address realms use
overlapping addressing space, then there is a risk that the DNS
server provides information that is not useful to the Device.
4. Identify requirements for longer-term, sound technical solutions;
contribute to the process of finding the right longer-term
solution.
Thomson & Bellis Standards Track [Page 15]
RFC 7216 LIS Discovery by IP April 2014
A longer-term solution is already provided in [RFC5986].
However, that solution relies on widespread deployment. The
UNSAF solution provided here is an interim solution that enables
LIS access for Devices that are not able to benefit from
deployment of the recommendations in [RFC5986].
5. Discussion of the impact of the noted practical issues with
existing deployed NATs and experience reports.
The UNSAF mechanism depends on the experience in deployment of
STUN [RFC5389]. On the whole, existing residential gateway
devices are able to provide access to STUN and DNS service
reliably, although regard should be given to the size of the DNS
response (see [RFC5625]).
8. Acknowledgements
Richard Barnes provided the text in Section 5.
9. References
9.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)", RFC 5986, September
2010.
[RFC7105] Thomson, M. and J. Winterbottom, "Using Device-Provided
Location-Related Measurements in Location Configuration
Protocols", RFC 7105, January 2014.
9.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
Thomson & Bellis Standards Track [Page 16]
RFC 7216 LIS Discovery by IP April 2014
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral
Self-Address Fixing (UNSAF) Across Network Address
Translation", RFC 3424, November 2002.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010.
[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
BCP 160, RFC 6280, July 2011.
[RFC6303] Andrews, M., "Locally Served DNS Zones", BCP 163, RFC
6303, July 2011.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
[UPnP-IGD-WANIPConnection1]
UPnP Forum, "Internet Gateway Device (IGD) Standardized
Device Control Protocol V 1.0: WANIPConnection:1 Service
Template Version 1.01 For UPnP Version 1.0", DCP 05-001,
Nov. 2001, <http://upnp.org/specs/gw/
UPnP-gw-WANIPConnection-v1-Service.pdf>.
[RFC6886] Cheshire, S. and M. Krochmal, "NAT Port Mapping Protocol
(NAT-PMP)", RFC 6886, April 2013.
Thomson & Bellis Standards Track [Page 17]
RFC 7216 LIS Discovery by IP April 2014
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", BCP
152, RFC 5625, August 2009.
[RFC5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)", RFC
5985, September 2010.
Authors' Addresses
Martin Thomson
Mozilla
Suite 300
650 Castro Street
Mountain View, CA 94041
US
EMail: martin.thomson@gmail.com
Ray Bellis
Nominet UK
Edmund Halley Road
Oxford OX4 4DQ
United Kingdom
Phone: +44 1865 332211
EMail: ray.bellis@nominet.org.uk
URI: http://www.nominet.org.uk/
Thomson & Bellis Standards Track [Page 18]