Independent Submission J. Abley
Request for Comments: 7108 Dyn, Inc.
Category: Informational T. Manderson
ISSN: 2070-1721 ICANN
January 2014
A Summary of Various Mechanisms Deployed at L-Root for the
Identification of Anycast Nodes
Abstract
Anycast is a deployment technique commonly employed for
authoritative-only servers in the Domain Name System (DNS). L-Root,
one of the thirteen root servers, is deployed in this fashion.
Various techniques have been used to map deployed anycast
infrastructure externally, i.e., without reference to inside
knowledge about where and how such infrastructure has been deployed.
Motivations for performing such measurement exercises include
operational troubleshooting and infrastructure risk assessment. In
the specific case of L-Root, the ability to measure and map anycast
infrastructure using the techniques mentioned in this document is
provided for reasons of operational transparency.
This document describes all facilities deployed at L-Root to
facilitate mapping of its infrastructure and serves as documentation
for L-Root as a measurable service.
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 a candidate for any level of Internet
Standard; see 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/rfc7108.
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Naming Scheme for L-Root Nodes . . . . . . . . . . . . . . . 3
4. Identification of L-Root Nodes . . . . . . . . . . . . . . . 3
4.1. Use of NSID . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Use of HOSTNAME.BIND/CH/TXT . . . . . . . . . . . . . . . 5
4.3. Use of ID.SERVER/CH/TXT . . . . . . . . . . . . . . . . . 6
4.4. Use of IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT and .../IN/A . 6
4.5. Use of NODES.L.ROOT-SERVERS.ORG/IN/TXT . . . . . . . . . 8
5. Provisioning of IDENTITY.L.ROOT-SERVERS.ORG . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
1. Introduction
The Domain Name System (DNS) is described in [RFC1034] and [RFC1035].
L-Root, one of the thirteen root servers, is deployed using anycast
[RFC4786]; its service addresses, published in the A and AAAA
Resource Record (RR) Sets for "L.ROOT-SERVERS.NET", are made
available from a substantial number of semi-autonomous servers
deployed throughout the Internet. A list of locations served by
L-Root can be found at [ROOT-SERVERS].
Various techniques have been used to map deployed anycast
infrastructure externally, i.e., without reference to inside
knowledge about where and how such infrastructure has been deployed.
Motivations for performing such measurement exercises include
operational troubleshooting and infrastructure risk assessment. In
the specific case of L-Root, the ability to measure and map anycast
infrastructure using the techniques mentioned in this document is
provided for reasons of operational transparency.
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This document describes all facilities currently provided at L-Root
to aid node identification.
2. Conventions Used in This Document
This document contains several examples of commands typed at a Unix
(or Unix-like) command line to illustrate use of the various
mechanisms available to identify L-Root nodes. Such examples are
presented in this document with lines typed by the user preceded by
the "%" prompt character; a bare "%" character indicates the end of
the output resulting from the command.
In some cases, the output shown in examples is too long to be
represented directly in the text. In those cases, a backslash
character ("\") is used to indicate continuation.
3. Naming Scheme for L-Root Nodes
Individual L-Root nodes have structured hostnames that are
constructed as follows:
<IATA Code><NN>.L.ROOT-SERVERS.ORG
where
o <IATA Code> is chosen from the list of three-character airport
codes published by the International Air Transport Association
(IATA) in the IATA Airline Coding Directory [ACD]; and
o <NN> is a two-digit numeric code used to distinguish between two
different nodes in the vicinity of the same airport.
Where multiple airports exist in the vicinity of a single L-Root
node, one is arbitrarily chosen.
More granular location data published for L-Root nodes (e.g., see
Section 4.4) is derived from the location of the airport, not the
actual location of the node.
4. Identification of L-Root Nodes
L-Root service is provided using a single IPv4 address (199.7.83.42)
and a single IPv6 address (2001:500:3::42). Note that it is
preferable to refer to the service using its DNS name (L.ROOT-
SERVERS.NET) rather than literal addresses, since addresses can
change from time to time.
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At the time of writing, there are 273 separate name server elements
("nodes") deployed in 143 locations: together, these nodes provide
L-Root service. A DNS query sent to an L-Root service address will
be routed towards exactly one of those nodes for processing, and the
corresponding DNS response will be originated from the same node.
Queries from different clients may be routed to different nodes.
Successive queries from the same client may also be routed to
different nodes.
The following sections provide a summary of all mechanisms provided
by L-Root to allow a client to identify which L-Root node is being
used.
Using HOSTNAME.BIND/CH/TXT (Section 4.2), ID.SERVER/CH/TXT
(Section 4.3), or IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT or IDENTITY.L
.ROOT-SERVERS/IN/A (Section 4.4) to identify a node for the purposes
of reporting a problem is frequently reasonable, but it should be
acknowledged that there is potential for re-routing between
successive queries: an observed problem might relate to one node,
whilst a subsequent query using one of those three techniques could
be answered by a different node. Use of the Name Server Identifier
(NSID) option on the precise queries that yield problematic responses
can obviate this possibility (see Section 4.1).
4.1. Use of NSID
L-Root supports the use of the Name Server Identifier (NSID) option
[RFC5001] to return the identity of an L-Root node along with the
response to a DNS query. The NSID payload of such responses is the
fully qualified hostname of the responding L-Root node.
The NSID option allows the identification of a node sending a
specific, requested response to the client. This is of particular
use if (for example) there is a desire to identify unequivocally what
node is responding with a particularly troublesome response; the
output of the diagnostic tool "dig" with NSID requested provides the
problem response with the node identification, and its output in that
case could form the basis of a useful trouble report.
NSID is specified as an EDNS(0) option [RFC6891]. Clients that do
not support EDNS(0) signaling (or depend on other systems that do not
support EDNS0) may find this mechanism unavailable.
The NSID option can be specified using the widely used diagnostic
tool "dig" using the "+nsid" option, as shown below. Note that long
lines have been truncated for the purposes of this document ("\" at
the end of a line indicates continuation).
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% dig -4 @L.ROOT-SERVERS.NET . SOA +nsid \
+norec +noall +comments
; <<>> DiG 9.6.-ESV-R3 <<>> -4 @L.ROOT-SERVERS.NET . SOA +nsid \
+norec +noall +comments
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14913
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 23
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; NSID: 79 74 7a 30 31 2e 6c 2e 72 6f 6f 74 2d 73 65 72 76 65 72 73 \
2e 6f 72 67 (y) (t) (z) (0) (1) (.) (l) (.) (r) (o) (o) (t) (-) \
(s) (e) (r) (v) (e) (r) (s) (.) (o) (r) (g)
%
% dig -6 @L.ROOT-SERVERS.NET . SOA +nsid \
+norec +noall +comments
; <<>> DiG 9.6.-ESV-R3 <<>> -6 @L.ROOT-SERVERS.NET . SOA +nsid \
+norec +noall +comments
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33374
;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 23
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; NSID: 79 74 7a 30 31 2e 6c 2e 72 6f 6f 74 2d 73 65 72 76 65 72 73 \
2e 6f 72 67 (y) (t) (z) (0) (1) (.) (l) (.) (r) (o) (o) (t) (-) \
(s) (e) (r) (v) (e) (r) (s) (.) (o) (r) (g)
%
4.2. Use of HOSTNAME.BIND/CH/TXT
L-Root supports the use of HOSTNAME.BIND/CH/TXT queries to return the
identity of an L-Root node. The TXT RDATA returned is the fully
qualified hostname of the responding L-Root node.
The HOSTNAME.BIND/CH/TXT convention is described in [RFC4892].
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% dig -4 @L.ROOT-SERVERS.NET HOSTNAME.BIND CH TXT +short
"ytz01.l.root-servers.org"
%
% dig -6 @L.ROOT-SERVERS.NET HOSTNAME.BIND CH TXT +short
"ytz01.l.root-servers.org"
%
4.3. Use of ID.SERVER/CH/TXT
L-Root supports the use of ID.SERVER/CH/TXT queries to return the
identity of an L-Root node. The TXT RDATA returned is the fully
qualified hostname of the responding L-Root node.
ID.SERVER/CH/TXT functions identically (apart from the QNAME) to
HOSTNAME.BIND/CH/TXT, as discussed in Section 4.2. The discussion
there relating to the possibility of re-routing between successive
queries also follows for ID.SERVER/CH/TXT.
The ID.SERVER/CH/TXT convention is described in [RFC4892].
% dig -4 @L.ROOT-SERVERS.NET ID.SERVER CH TXT +short
"ytz01.l.root-servers.org"
%
% dig -6 @L.ROOT-SERVERS.NET ID.SERVER CH TXT +short
"ytz01.l.root-servers.org"
%
4.4. Use of IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT and .../IN/A
The operator of L-Root has distributed a separate DNS service in
parallel with L-Root, operating on precisely the same set of nodes
but listening on addresses that are different from the L-Root service
addresses. Measurements of this separate service should give results
that are representative of L-Root. Further discussion of this
service can be found in Section 5.
The fully qualified DNS name IDENTITY.L.ROOT-SERVERS.ORG (note the
use of ORG, not NET) has associated TXT and A RR Sets that are unique
to the responding node. Clients are hence able to issue queries for
IDENTITY.L.ROOT-SERVERS.ORG/IN/A and IDENTITY.L.ROOT-SERVERS.ORG/IN/
TXT and use the results both to identify individual nodes and to
distinguish between responses generated by different nodes.
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The TXT record returned in the response to such queries is structured
as follows:
1. The fully qualified hostname of the node responding to the query;
2. The city in which the node is located;
3. The region in which the node is located, if applicable;
4. The economy in which the node is located (in most cases, the name
of a country); and
5. The Internet Corporation for Assigned Names and Numbers (ICANN)
region in which the node is located. A list of ICANN regions at
the time of writing can be found at <http://meetings.icann.org/
regions>.
The A record returned in the response to such queries is guaranteed
to be unique to the responding node. The A RRType was chosen in an
effort to make the use of this mechanism as widely available to
client environments as possible, and the ability to map a hostname to
an IPv4 address seemed more likely to be widespread than the mapping
of a hostname to any other value. It should be noted that the
availability of this mechanism to any particular client is orthogonal
to the local availability of IPv4 or IPv6 transport.
In this case, because identity data is published using IN-class
resource records, it is not necessary to send queries directly
towards L-Root in order to obtain results. Responses can be obtained
through recursive servers, the responses in those cases being the
identity of L-Root as observed through the recursive server used
rather than the "closest" L-Root node to the client. This
facilitates some degree of remote troubleshooting, since a query for
IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT or IDENTITY.L.ROOT-SERVERS.ORG/IN/
A directed a remote recursive resolver can help illustrate which
L-Root node is being used by that server (or was used when the cache
was populated).
A related caching effect is that responses to IDENTITY.L.ROOT-
SERVERS.ORG/IN/A and IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT may be cached
at different times, and may hence persist in a cache for overlapping
periods of time. One possible visible effect is that the responses
to IDENTITY.L.ROOT-SERVERS.ORG/IN/A and IDENTITY.L.ROOT-SERVERS.ORG/
IN/TXT as presented from a cache may appear to be incoherent (i.e.,
refer to different nodes) despite queries against of the cache
happening (near) simultaneously. Caches may also discard the
published Times to Live (TTLs) in responses from the authoritative
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server and replace them with longer TTLs, as a matter of local
policy. Interpretation of responses for these queries from caches
should therefore be carried out with these possible effects in mind.
It has been observed that IDENTITY.L.ROOT-SERVERS.ORG/IN/A queries
offer a useful mechanism for troubleshooting DNS problems with non-
technical users, since such users can often be walked through the
process of looking up an A record (e.g., as a side effect of
utilities such as ping) far easier than they can be instructed on how
to use DNS-specific tools such as dig.
% dig IDENTITY.L.ROOT-SERVERS.ORG TXT +short
"ytz01.l.root-servers.org" "Toronto" "Ontario" "Canada" "NorthAmerica"
%
% dig IDENTITY.L.ROOT-SERVERS.ORG A +short
67.215.199.91
%
4.5. Use of NODES.L.ROOT-SERVERS.ORG/IN/TXT
The fully qualified DNS name NODES.L.ROOT-SERVERS.ORG (note again the
use of ORG, not NET) provides multiple TXT RRs, one per node, and
represents the effective concatenation of all possible responses to
the query IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT.
Note that in the example below we have forced dig to send the query
over TCP, since we expect the response to be too large for UDP
transport to accommodate. Note also that the list shown is truncated
for clarity, and can be expected to change from time to time as new
L-Root nodes are provisioned and old ones decommissioned.
% dig NODES.L.ROOT-SERVERS.ORG TXT +short +tcp | head -10
"abj01.l.root-servers.org" "Abidjan" "" "Cote d'Ivoire" "Africa"
"abj02.l.root-servers.org" "Abidjan" "" "Cote d'Ivoire" "Africa"
"akl01.l.root-servers.org" "Mangere" "" "New Zealand" "AsiaPacific"
"akl41.l.root-servers.org" "Mangere" "" "New Zealand" "AsiaPacific"
"akl42.l.root-servers.org" "Mangere" "" "New Zealand" "AsiaPacific"
"akl43.l.root-servers.org" "Mangere" "" "New Zealand" "AsiaPacific"
"akl44.l.root-servers.org" "Mangere" "" "New Zealand" "AsiaPacific"
"ams01.l.root-servers.org" "Haarlemmermeer" "" "Netherlands" "Europe"
"anc01.l.root-servers.org" "Anchorage" "Alaska" "United States" \
"NorthAmerica"
%
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5. Provisioning of IDENTITY.L.ROOT-SERVERS.ORG
Individual L-Root nodes run a dedicated, separate authority-only DNS
server process that serves the IDENTITY.L.ROOT-SERVERS.ORG zone. The
contents of that zone are unique to every node; hence, each
responding node will generate a node-specific response.
The contents of the IDENTITY.L.ROOT-SERVERS.ORG zone are hence
deliberately incoherent, the apparent zone contents depending on the
node responding to the corresponding query.
The IDENTITY.L.ROOT-SERVERS.ORG zone is delegated to the single name
server BEACON.L.ROOT-SERVERS.ORG, numbered on IPv4 and IPv6 addresses
that are covered by the same routing advertisements that cover the
L-Root service addresses. Reachability of BEACON.L.ROOT-SERVERS.ORG
is hence well-aligned with the reachability of L.ROOT-SERVERS.NET;
therefore, measurement of the IDENTITY service ought to give similar
results to measurement of the L-Root service.
It is considered best practice always to delegate a DNS zone to more
than one name server [RFC2182]; however, as described, the IDENTITY.L
.ROOT-SERVERS.ORG zone is delegated to just one server. Ordinarily,
this would present a risk of failure if that single server is not
available; however, given the purpose of the delegation in this case
and that the expected mitigation of a failure in a single node is the
routing of a query to a different node, delegation to a single server
in this particular use-case is effective.
At the time of writing, the ROOT-SERVERS.ORG zone is not signed with
DNSSEC. When DNSSEC is deployed in that zone, the L.ROOT-SERVERS.ORG
zone will also be signed. This will facilitate secure responses for
queries for BEACON.L.ROOT-SERVERS.ORG and NODES.L.ROOT-SERVERS.ORG.
Secure responses for IDENTITY.L.ROOT-SERVERS.ORG are unlikely to
become available even with the deployment of DNSSEC in the parent,
since the implementation of the IDENTITY.L.ROOT-SERVERS.ORG service
involves widely distributed static zone data. Management of key
materials distributed to every L-Root node would be impractical to
audit, and signatures returned in secure responses would be
correspondingly of low value.
6. Security Considerations
Some operators of anycast services choose not to disclose locations
(or even numbers) of nodes, citing security concerns. The operator
of L-Root considers that none of the published information described
in this document is truly secret, since any service element that
provides service to the Internet can never truly be obscured from
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view. Given that location information can be found regardless of any
conscious, deliberate disclosure, and since easy access to this
information has diagnostic value, the operator of L-Root has adopted
a policy of operational transparency.
The information presented in this document presents no new threat to
the Internet.
7. Acknowledgements
The aspects of the L-Root service that were deployed to facilitate
IN-class mapping were discussed and implemented as part of an
informal collaboration with Xun Fan, John Heidemann, and Ramesh
Govidan, whose contributions are acknowledged. The motivation to
facilitate mapping of L-Root as an anycast service using IN-class
queries was inspired by [Fan2013].
Helpful reviews and comments from Gaurab Upadhaya, Hugo Salgado,
Brian Dixon, Bob Harold, Paul Hoffman, Jakob Schlyter, Andrew
Sullivan, Bruce Campbell, S. Moonesamy, and Stephane Bortzmeyer on
earlier versions of this document were very much appreciated.
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2182] Elz, R., Bush, R., Bradner, S., and M. Patton, "Selection
and Operation of Secondary DNS Servers", BCP 16, RFC 2182,
July 1997.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, December 2006.
[RFC4892] Woolf, S. and D. Conrad, "Requirements for a Mechanism
Identifying a Name Server Instance", RFC 4892, June 2007.
[RFC5001] Austein, R., "DNS Name Server Identifier (NSID) Option",
RFC 5001, August 2007.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.
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8.2. Informative References
[ACD] International Air Transport Association (IATA), "Airline
Coding Directory (ACD)", 2013,
<http://www.iata.org/publications/Pages/coding.aspx>.
[Fan2013] Fan, X., Heidemann, J., and R. Govidan, "Evaluating
Anycast in the Domain Name System", Proceedings of the
IEEE Infocom Turin, Italy, April 2013.
[ROOT-SERVERS]
"root-servers.org", <http://www.root-servers.org>.
Authors' Addresses
Joe Abley
Dyn, Inc.
470 Moore Street
London, ON N6C 2C2
Canada
Phone: +1 519 670 9327
EMail: jabley@dyn.com
Terry Manderson
ICANN
12025 Waterfront Drive
Suite 300
Los Angeles, CA 90094-2536
USA
EMail: terry.manderson@icann.org
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