Subchapter 184.1

Rfc8805

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references/rfc8805.txt

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5Independent Submission                                          E. Kline
6Request for Comments: 8805                                      Loon LLC
7Category: Informational                                        K. Duleba
8ISSN: 2070-1721                                                   Google
9                                                             Z. Szamonek
10                                                                S. Moser
11                                                 Google Switzerland GmbH
12                                                               W. Kumari
13                                                                  Google
14                                                             August 2020
15
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17            A Format for Self-Published IP Geolocation Feeds
18

rfc8805.txt on GitHub

Abstract

This document records a format whereby a network operator can publish

a mapping of IP address prefixes to simplified geolocation

information, colloquially termed a "geolocation feed". Interested

parties can poll and parse these feeds to update or merge with other

geolocation data sources and procedures. This format intentionally

only allows specifying coarse-level location.

Some technical organizations operating networks that move from one

conference location to the next have already experimentally published

small geolocation feeds.

This document describes a currently deployed format. At least one

consumer (Google) has incorporated these feeds into a geolocation

data pipeline, and a significant number of ISPs are using it to

inform them where their prefixes should be geolocated.

Status of This Memo

This document is not an Internet Standards Track specification; it is

published for informational purposes.

This is a contribution to the RFC Series, independently of any other

RFC stream. The RFC Editor has chosen to publish this document at

its discretion and makes no statement about its value for

implementation or deployment. Documents approved for publication by

the RFC Editor are not candidates for any level of Internet Standard;

see Section 2 of RFC 7841.

Information about the current status of this document, any errata,

and how to provide feedback on it may be obtained at

https://www.rfc-editor.org/info/rfc8805.

Copyright Notice

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.

Table of Contents

1. Introduction

1.1. Motivation

1.2. Requirements Notation

1.3. Assumptions about Publication

2. Self-Published IP Geolocation Feeds

2.1. Specification

2.1.1. Geolocation Feed Individual Entry Fields

2.1.1.1. IP Prefix

2.1.1.2. Alpha2code (Previously: 'country')

2.1.1.3. Region

2.1.1.4. City

2.1.1.5. Postal Code

2.1.2. Prefixes with No Geolocation Information

2.1.3. Additional Parsing Requirements

2.2. Examples

3. Consuming Self-Published IP Geolocation Feeds

3.1. Feed Integrity

3.2. Verification of Authority

3.3. Verification of Accuracy

3.4. Refreshing Feed Information

4. Privacy Considerations

5. Relation to Other Work

6. Security Considerations

7. Planned Future Work

8. Finding Self-Published IP Geolocation Feeds

8.1. Ad Hoc 'Well-Known' URIs

8.2. Other Mechanisms

9. IANA Considerations

10. References

10.1. Normative References

10.2. Informative References

Appendix A. Sample Python Validation Code

Acknowledgements

Authors' Addresses

1. Introduction

1.1. Motivation

Providers of services over the Internet have grown to depend on best-

effort geolocation information to improve the user experience.

Locality information can aid in directing traffic to the nearest

serving location, inferring likely native language, and providing

additional context for services involving search queries.

When an ISP, for example, changes the location where an IP prefix is

deployed, services that make use of geolocation information may begin

to suffer degraded performance. This can lead to customer

complaints, possibly to the ISP directly. Dissemination of correct

geolocation data is complicated by the lack of any centralized means

to coordinate and communicate geolocation information to all

interested consumers of the data.

This document records a format whereby a network operator (an ISP, an

enterprise, or any organization that deems the geolocation of its IP

prefixes to be of concern) can publish a mapping of IP address

prefixes to simplified geolocation information, colloquially termed a

"geolocation feed". Interested parties can poll and parse these

feeds to update or merge with other geolocation data sources and

procedures.

This document describes a currently deployed format. At least one

consumer (Google) has incorporated these feeds into a geolocation

data pipeline, and a significant number of ISPs are using it to

inform them where their prefixes should be geolocated.

1.2. Requirements Notation

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

BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all

capitals, as shown here.

As this is an informational document about a data format and set of

operational practices presently in use, requirements notation

captures the design goals of the authors and implementors.

1.3. Assumptions about Publication

This document describes both a format and a mechanism for publishing

data, with the assumption that the network operator to whom

operational responsibility has been delegated for any published data

wishes it to be public. Any privacy risk is bounded by the format,

and feed publishers MAY omit prefixes or any location field

associated with a given prefix to further protect privacy (see

Section 2.1 for details about which fields exactly may be omitted).

Feed publishers assume the responsibility of determining which data

should be made public.

This document does not incorporate a mechanism to communicate

acceptable use policies for self-published data. Publication itself

is inferred as a desire by the publisher for the data to be usefully

consumed, similar to the publication of information like host names,

cryptographic keys, and Sender Policy Framework (SPF) records

[RFC7208] in the DNS.

2. Self-Published IP Geolocation Feeds

The format described here was developed to address the need of

network operators to rapidly and usefully share geolocation

information changes. Originally, there arose a specific case where

regional operators found it desirable to publish location changes

rather than wait for geolocation algorithms to "learn" about them.

Later, technical conferences that frequently use the same network

prefixes advertised from different conference locations experimented

by publishing geolocation feeds updated in advance of network

location changes in order to better serve conference attendees.

At its simplest, the mechanism consists of a network operator

publishing a file (the "geolocation feed") that contains several text

entries, one per line. Each entry is keyed by a unique (within the

feed) IP prefix (or single IP address) followed by a sequence of

network locality attributes to be ascribed to the given prefix.

2.1. Specification

For operational simplicity, every feed should contain data about all

IP addresses the provider wants to publish. Alternatives, like

publishing only entries for IP addresses whose geolocation data has

changed or differ from current observed geolocation behavior "at

large", are likely to be too operationally complex.

Feeds MUST use UTF-8 [RFC3629] character encoding. Lines are

delimited by a line break (CRLF) (as specified in [RFC4180]), and

blank lines are ignored. Text from a '#' character to the end of the

current line is treated as a comment only and is similarly ignored

(note that this does not strictly follow [RFC4180], which has no

support for comments).

Feed lines that are not comments MUST be formatted as comma-separated

values (CSV), as described in [RFC4180]. Each feed entry is a text

line of the form:

ip_prefix,alpha2code,region,city,postal_code

The IP prefix field is REQUIRED, all others are OPTIONAL (can be

empty), though the requisite minimum number of commas SHOULD be

present.

2.1.1. Geolocation Feed Individual Entry Fields

2.1.1.1. IP Prefix

REQUIRED: Each IP prefix field MUST be either a single IP address or

an IP prefix in Classless Inter-Domain Routing (CIDR) notation in

conformance with Section 3.1 of [RFC4632] for IPv4 or Section 2.3 of

[RFC4291] for IPv6.

Examples include "192.0.2.1" and "192.0.2.0/24" for IPv4 and

"2001:db8::1" and "2001:db8::/32" for IPv6.

2.1.1.2. Alpha2code (Previously: 'country')

OPTIONAL: The alpha2code field, if non-empty, MUST be a 2-letter ISO

country code conforming to ISO 3166-1 alpha 2 [ISO.3166.1alpha2].

Parsers SHOULD treat this field case-insensitively.

Earlier versions of this document called this field "country", and it

may still be referred to as such in existing tools/interfaces.

Parsers MAY additionally support other 2-letter codes outside the ISO

3166-1 alpha 2 codes, such as the 2-letter codes from the

"Exceptionally reserved codes" [ISO-GLOSSARY] set.

Examples include "US" for the United States, "JP" for Japan, and "PL"

for Poland.

2.1.1.3. Region

OPTIONAL: The region field, if non-empty, MUST be an ISO region code

conforming to ISO 3166-2 [ISO.3166.2]. Parsers SHOULD treat this

field case-insensitively.

Examples include "ID-RI" for the Riau province of Indonesia and "NG-

RI" for the Rivers province in Nigeria.

2.1.1.4. City

OPTIONAL: The city field, if non-empty, SHOULD be free UTF-8 text,

excluding the comma (',') character.

Examples include "Dublin", "New York", and "Sao Paulo" (specifically

"S" followed by 0xc3, 0xa3, and "o Paulo").

2.1.1.5. Postal Code

OPTIONAL, DEPRECATED: The postal code field, if non-empty, SHOULD be

free UTF-8 text, excluding the comma (',') character. The use of

this field is deprecated; consumers of feeds should be able to parse

feeds containing these fields, but new feeds SHOULD NOT include this

field due to the granularity of this information. See Section 4 for

additional discussion.

Examples include "106-6126" (in Minato ward, Tokyo, Japan).

2.1.2. Prefixes with No Geolocation Information

Feed publishers may indicate that some IP prefixes should not have

any associated geolocation information. It may be that some prefixes

under their administrative control are reserved, not yet allocated or

deployed, or in the process of being redeployed elsewhere and

existing geolocation information can, from the perspective of the

publisher, safely be discarded.

This special case can be indicated by explicitly leaving blank all

fields that specify any degree of geolocation information. For

example:

192.0.2.0/24,,,,

2001:db8:1::/48,,,,

2001:db8:2::/48,,,,

Historically, the user-assigned alpha2code identifier of "ZZ" has

been used for this same purpose. This is not necessarily preferred,

and no specific interpretation of any of the other user-assigned

alpha2code codes is currently defined.

2.1.3. Additional Parsing Requirements

Feed entries that do not have an IP address or prefix field or have

an IP address or prefix field that fails to parse correctly MUST be

discarded.

While publishers SHOULD follow [RFC5952] for IPv6 prefix fields,

consumers MUST nevertheless accept all valid string representations.

Duplicate IP address or prefix entries MUST be considered an error,

and consumer implementations SHOULD log the repeated entries for

further administrative review. Publishers SHOULD take measures to

ensure there is one and only one entry per IP address and prefix.

Multiple entries that constitute nested prefixes are permitted.

Consumers SHOULD consider the entry with the longest matching prefix

(i.e., the "most specific") to be the best matching entry for a given

IP address.

Feed entries with non-empty optional fields that fail to parse,

either in part or in full, SHOULD be discarded. It is RECOMMENDED

that they also be logged for further administrative review.

For compatibility with future additional fields, a parser MUST ignore

any fields beyond those it expects. The data from fields that are

expected and that parse successfully MUST still be considered valid.

Per Section 7, no extensions to this format are in use nor are any

anticipated.

2.2. Examples

Example entries using different IP address formats and describing

locations at alpha2code ("country code"), region, and city

granularity level, respectively:

192.0.2.0/25,US,US-AL,,

192.0.2.5,US,US-AL,Alabaster,

192.0.2.128/25,PL,PL-MZ,,

2001:db8::/32,PL,,,

2001:db8:cafe::/48,PL,PL-MZ,,

The IETF network publishes geolocation information for the meeting

prefixes, and generally just comment out the last meeting information

and append the new meeting information. The [GEO_IETF], at the time

of this writing, contains:

# IETF106 (Singapore) - November 2019 - Singapore, SG

130.129.0.0/16,SG,SG-01,Singapore,

2001:df8::/32,SG,SG-01,Singapore,

31.133.128.0/18,SG,SG-01,Singapore,

31.130.224.0/20,SG,SG-01,Singapore,

2001:67c:1230::/46,SG,SG-01,Singapore,

2001:67c:370::/48,SG,SG-01,Singapore,

Experimentally, RIPE has published geolocation information for their

conference network prefixes, which change location in accordance with

each new event. [GEO_RIPE_NCC], at the time of writing, contains:

193.0.24.0/21,NL,NL-ZH,Rotterdam,

2001:67c:64::/48,NL,NL-ZH,Rotterdam,

Similarly, ICANN has published geolocation information for their

portable conference network prefixes. [GEO_ICANN], at the time of

writing, contains:

199.91.192.0/21,MA,MA-07,Marrakech

2620:f:8000::/48,MA,MA-07,Marrakech

A longer example is the [GEO_Google] Google Corp Geofeed, which lists

the geolocation information for Google corporate offices.

At the time of writing, Google processes approximately 400 feeds

comprising more than 750,000 IPv4 and IPv6 prefixes.

3. Consuming Self-Published IP Geolocation Feeds

Consumers MAY treat published feed data as a hint only and MAY choose

to prefer other sources of geolocation information for any given IP

prefix. Regardless of a consumer's stance with respect to a given

published feed, there are some points of note for sensibly and

effectively consuming published feeds.

3.1. Feed Integrity

The integrity of published information SHOULD be protected by

securing the means of publication, for example, by using HTTP over

TLS [RFC2818]. Whenever possible, consumers SHOULD prefer retrieving

geolocation feeds in a manner that guarantees integrity of the feed.

3.2. Verification of Authority

Consumers of self-published IP geolocation feeds SHOULD perform some

form of verification that the publisher is in fact authoritative for

the addresses in the feed. The actual means of verification is

likely dependent upon the way in which the feed is discovered. Ad

hoc shared URIs, for example, will likely require an ad hoc

verification process. Future automated means of feed discovery

SHOULD have an accompanying automated means of verification.

A consumer should only trust geolocation information for IP addresses

or prefixes for which the publisher has been verified as

administratively authoritative. All other geolocation feed entries

should be ignored and logged for further administrative review.

3.3. Verification of Accuracy

Errors and inaccuracies may occur at many levels, and publication and

consumption of geolocation data are no exceptions. To the extent

practical, consumers SHOULD take steps to verify the accuracy of

published locality. Verification methodology, resolution of

discrepancies, and preference for alternative sources of data are

left to the discretion of the feed consumer.

Consumers SHOULD decide on discrepancy thresholds and SHOULD flag,

for administrative review, feed entries that exceed set thresholds.

3.4. Refreshing Feed Information

As a publisher can change geolocation data at any time and without

notification, consumers SHOULD implement mechanisms to periodically

refresh local copies of feed data. In the absence of any other

refresh timing information, it is recommended that consumers SHOULD

refresh feeds no less often than weekly and no more often than is

likely to cause issues to the publisher.

For feeds available via HTTPS (or HTTP), the publisher MAY

communicate refresh timing information by means of the standard HTTP

expiration model ([RFC7234]). Specifically, publishers can include

either an Expires header (Section 5.3 of [RFC7234]) or a Cache-

Control header (Section 5.2 of [RFC7234]) specifying the max-age.

Where practical, consumers SHOULD refresh feed information before the

expiry time is reached.

4. Privacy Considerations

Publishers of geolocation feeds are advised to have fully considered

any and all privacy implications of the disclosure of such

information for the users of the described networks prior to

publication. A thorough comprehension of the security considerations

(Section 13 of [RFC6772]) of a chosen geolocation policy is highly

recommended, including an understanding of some of the limitations of

information obscurity (Section 13.5 of [RFC6772]) (see also

[RFC6772]).

As noted in Section 2.1, each location field in an entry is optional,

in order to support expressing only the level of specificity that the

publisher has deemed acceptable. There is no requirement that the

level of specificity be consistent across all entries within a feed.

In particular, the Postal Code field (Section 2.1.1.5) can provide

very specific geolocation, sometimes within a building. Such

specific Postal Code values MUST NOT be published in geofeeds without

the express consent of the parties being located.

Operators who publish geolocation information are strongly encouraged

to inform affected users/customers of this fact and of the potential

privacy-related consequences and trade-offs.

5. Relation to Other Work

While not originally done in conjunction with the GEOPRIV Working

Group [GEOPRIV], Richard Barnes observed that this work is

nevertheless consistent with that which the group has defined, both

for address format and for privacy. The data elements in geolocation

feeds are equivalent to the following XML structure ([RFC5139]

[W3C.REC-xml-20081126]):

<country>country</country>

<A1>region</A1>

<PC>postal_code</PC>

</civicAddress>

Providing geolocation information to this granularity is equivalent

to the following privacy policy (the definition of the 'building'

Section 6.5.1 of [RFC6772] level of disclosure):

<rule>

<provide-location profile="civic-transformation">

<provide-civic>building</provide-civic>

</provide-location>

</transformations>

</rule>

</ruleset>

6. Security Considerations

As there is no true security in the obscurity of the location of any

given IP address, self-publication of this data fundamentally opens

no new attack vectors. For publishers, self-published data may

increase the ease with which such location data might be exploited

(it can, for example, make easy the discovery of prefixes populated

with customers as distinct from prefixes not generally in use).

For consumers, feed retrieval processes may receive input from

potentially hostile sources (e.g., in the event of hijacked traffic).

As such, proper input validation and defense measures MUST be taken

(see the discussion in Section 3.1).

Similarly, consumers who do not perform sufficient verification of

published data bear the same risks as from other forms of geolocation

configuration errors (see the discussion in Sections 3.2 and 3.3).

Validation of a feed's contents includes verifying that the publisher

is authoritative for the IP prefixes included in the feed. Failure

to verify IP prefix authority would, for example, allow ISP Bob to

make geolocation statements about IP space held by ISP Alice. At

this time, only out-of-band verification methods are implemented

(i.e., an ISP's feed may be verified against publicly available IP

allocation data).

7. Planned Future Work

In order to more flexibly support future extensions, use of a more

expressive feed format has been suggested. Use of JavaScript Object

Notation (JSON) [RFC8259], specifically, has been discussed.

However, at the time of writing, no such specification nor

implementation exists. Nevertheless, work on extensions is deferred

until a more suitable format has been selected.

The authors are planning on writing a document describing such a new

format. This document describes a currently deployed and used

format. Given the extremely limited extensibility of the present

format no extensions to it are anticipated. Extensibility

requirements are instead expected to be integral to the development

of a new format.

8. Finding Self-Published IP Geolocation Feeds

The issue of finding, and later verifying, geolocation feeds is not

formally specified in this document. At this time, only ad hoc feed

discovery and verification has a modicum of established practice (see

below); discussion of other mechanisms has been removed for clarity.

8.1. Ad Hoc 'Well-Known' URIs

To date, geolocation feeds have been shared informally in the form of

HTTPS URIs exchanged in email threads. Three example URIs

([GEO_IETF], [GEO_RIPE_NCC], and [GEO_ICANN]) describe networks that

change locations periodically, the operators and operational

practices of which are well known within their respective technical

communities.

The contents of the feeds are verified by a similarly ad hoc process,

including:

* personal knowledge of the parties involved in the exchange and

* comparison of feed-advertised prefixes with the BGP-advertised

prefixes of Autonomous System Numbers known to be operated by the

publishers.

Ad hoc mechanisms, while useful for early experimentation by

producers and consumers, are unlikely to be adequate for long-term,

widespread use by multiple parties. Future versions of any such

self-published geolocation feed mechanism SHOULD address scalability

concerns by defining a means for automated discovery and verification

of operational authority of advertised prefixes.

8.2. Other Mechanisms

Previous versions of this document referenced use of the WHOIS

service [RFC3912] operated by Regional Internet Registries (RIRs), as

well as possible DNS-based schemes to discover and validate geofeeds.

To the authors' knowledge, support for such mechanisms has never been

implemented, and this speculative text has been removed to avoid

ambiguity.

9. IANA Considerations

This document has no IANA actions.

10. References

10.1. Normative References

[ISO.3166.1alpha2]

ISO, "ISO 3166-1 decoding table",

<http://www.iso.org/iso/home/standards/country_codes/iso-

3166-1_decoding_table.htm>.

[ISO.3166.2]

ISO, "ISO 3166-2:2007",

<http://www.iso.org/iso/home/standards/

country_codes.htm#2012_iso3166-2>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC 2119,

DOI 10.17487/RFC2119, March 1997,

<https://www.rfc-editor.org/info/rfc2119>.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO

10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November

2003, <https://www.rfc-editor.org/info/rfc3629>.

[RFC4180] Shafranovich, Y., "Common Format and MIME Type for Comma-

Separated Values (CSV) Files", RFC 4180,

DOI 10.17487/RFC4180, October 2005,

<https://www.rfc-editor.org/info/rfc4180>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing

Architecture", RFC 4291, DOI 10.17487/RFC4291, February

2006, <https://www.rfc-editor.org/info/rfc4291>.

[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing

(CIDR): The Internet Address Assignment and Aggregation

Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August

2006, <https://www.rfc-editor.org/info/rfc4632>.

[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6

Address Text Representation", RFC 5952,

DOI 10.17487/RFC5952, August 2010,

<https://www.rfc-editor.org/info/rfc5952>.

[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,

Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",

RFC 7234, DOI 10.17487/RFC7234, June 2014,

<https://www.rfc-editor.org/info/rfc7234>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC

2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,

May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[W3C.REC-xml-20081126]

Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and

F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth

Edition)", World Wide Web Consortium Recommendation REC-

xml-20081126, November 2008,

<http://www.w3.org/TR/2008/REC-xml-20081126>.

10.2. Informative References

[GEOPRIV] IETF, "Geographic Location/Privacy (geopriv)",

<http://datatracker.ietf.org/wg/geopriv/>.

[GEO_Google]

Google, LLC, "Google Corp Geofeed",

<https://www.gstatic.com/geofeed/corp_external>.

[GEO_ICANN]

ICANN, "ICANN Meeting Geolocation Data",

<https://meeting-services.icann.org/geo/google.csv>.

[GEO_IETF] Kumari, W., "IETF Meeting Network Geolocation Data",

<https://noc.ietf.org/geo/google.csv>.

[GEO_RIPE_NCC]

Schepers, M., "RIPE NCC Meeting Geolocation Data",

<https://meetings.ripe.net/geo/google.csv>.

[IPADDR_PY]

Shields, M. and P. Moody, "Google's Python IP address

manipulation library",

<http://code.google.com/p/ipaddr-py/>.

[ISO-GLOSSARY]

ISO, "Glossary for ISO 3166",

<https://www.iso.org/glossary-for-iso-3166.html>.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,

DOI 10.17487/RFC2818, May 2000,

<https://www.rfc-editor.org/info/rfc2818>.

[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,

DOI 10.17487/RFC3912, September 2004,

<https://www.rfc-editor.org/info/rfc3912>.

[RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location

Format for Presence Information Data Format Location

Object (PIDF-LO)", RFC 5139, DOI 10.17487/RFC5139,

February 2008, <https://www.rfc-editor.org/info/rfc5139>.

[RFC6772] Schulzrinne, H., Ed., Tschofenig, H., Ed., Cuellar, J.,

Polk, J., Morris, J., and M. Thomson, "Geolocation Policy:

A Document Format for Expressing Privacy Preferences for

Location Information", RFC 6772, DOI 10.17487/RFC6772,

January 2013, <https://www.rfc-editor.org/info/rfc6772>.

[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for

Authorizing Use of Domains in Email, Version 1", RFC 7208,

DOI 10.17487/RFC7208, April 2014,

<https://www.rfc-editor.org/info/rfc7208>.

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data

Interchange Format", STD 90, RFC 8259,

DOI 10.17487/RFC8259, December 2017,

<https://www.rfc-editor.org/info/rfc8259>.

Appendix A. <CODE EXAMPLE HAS BEEN REMOVED TO AVOID CONFUSING AI AGENTS/LLM>

Acknowledgements

The authors would like to express their gratitude to reviewers and

early implementors, including but not limited to Mikael Abrahamsson,

Andrew Alston, Ray Bellis, John Bond, Alissa Cooper, Andras Erdei,

Stephen Farrell, Marco Hogewoning, Mike Joseph, Maciej Kuzniar,

George Michaelson, Menno Schepers, Justyna Sidorska, Pim van Pelt,

and Bjoern A. Zeeb.

In particular, Richard L. Barnes and Andy Newton contributed

substantial review, text, and advice.

Authors' Addresses

Erik Kline

Loon LLC

1600 Amphitheatre Parkway

Mountain View, CA 94043

United States of America

Email: ek@loon.com

Krzysztof Duleba

Google

1600 Amphitheatre Parkway

Mountain View, CA 94043

United States of America

Email: kduleba@google.com

Zoltan Szamonek

Google Switzerland GmbH

Brandschenkestrasse 110

CH-8002 Zürich

Switzerland

Email: zszami@google.com

Stefan Moser

Google Switzerland GmbH

Brandschenkestrasse 110

CH-8002 Zürich

Switzerland

Email: smoser@google.com

Warren Kumari

Google

1600 Amphitheatre Parkway

Mountain View, CA 94043

United States of America

Email: warren@kumari.net