Network Working Group J. Abley
Internet-Draft ICANN
Intended status: Informational March 27, 2013
Expires: September 28, 2013
A Summary of Various Mechanisms Deployed at L-Root for the
Identification of Anycast Nodes
draft-jabley-dnsop-anycast-mapping-01
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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 2013.
Copyright Notice
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Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Naming Scheme for L-Root Nodes . . . . . . . . . . . . . . . . 4
3. Identification of L-Root Nodes . . . . . . . . . . . . . . . . 5
3.1. Use of NSID . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Use of HOSTNAME.BIND/CH/TXT . . . . . . . . . . . . . . . 6
3.3. Use of ID.SERVER/CH/TXT . . . . . . . . . . . . . . . . . 7
3.4. Use of IDENTITY.L.ROOT-SERVERS.ORG/IN/TXT and .../IN/A . . 7
3.5. Use of NODES.L.ROOT-SERVERS.ORG/IN/TXT . . . . . . . . . . 9
4. Provisioning of IDENTITY.L.ROOT-SERVERS.ORG . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Editorial Notes . . . . . . . . . . . . . . . . . . . 16
A.1. Change History . . . . . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
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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 <http://www.root-servers.org>.
[Fan2013] describes a technique using open DNS resolvers to
distribute mapping queries to the service addresses of authoritative-
only servers. This technique relies upon the ability to acquire
meaningful information about individual anycast nodes by means of an
IN-class query. At the time the experiments described in that paper
were conducted, such ability existed with AS112 servers [RFC6304] but
not with any root server. Modifications were subsequently made to
the infrastructure of the L-Root service to facilitate this
technique.
This document describes all facilities currently provided at L-Root
to aid node identification.
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2. 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 [1]; and
o <NN> is a two-digit numeric code used to distinguish between two
different locations 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 3.4) is derived from the lcoation of the airport, not the
actual location of the node.
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3. 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). It should be noted 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.
At the time of writing there are 273 separate name server elements
("nodes") deployed in 143 locations which together 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.
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.
3.1. 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 unequivocably 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 EDNS0 option [RFC2671]. Clients that do not
support EDNS0 signalling (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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[monster:~]% 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)
[monster:~]%
[monster:~]% 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)
[monster:~]%
3.2. 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].
Using HOSTNAME.BIND/CH/TXT 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 HOSTNAME.BIND/CH/TXT query could be answered by a
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different node. Use of the NSID option can obviate this possiblity
(see Section 3.1).
[monster:~]% dig -4 @L.ROOT-SERVERS.NET HOSTNAME.BIND CH TXT +short
"ytz01.l.root-servers.org"
[monster:~]%
[monster:~]% dig -6 @L.ROOT-SERVERS.NET HOSTNAME.BIND CH TXT +short
"ytz01.l.root-servers.org"
[monster:~]%
3.3. 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 3.2. 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].
[monster:~]% dig -4 @L.ROOT-SERVERS.NET ID.SERVER CH TXT +short
"ytz01.l.root-servers.org"
[monster:~]%
[monster:~]% dig -6 @L.ROOT-SERVERS.NET ID.SERVER CH TXT +short
"ytz01.l.root-servers.org"
[monster:~]%
3.4. 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.
Measurements of this separate service should give results which are
representative of L-Root. Further discussion of this service can be
found in Section 4.
The fully-qualified DNS name IDENTITY.L.ROOT-SERVERS.ORG (note the
use of ORG, not NET) has associated TXT and A RR Sets which 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 host name 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;
4. The economy in which the node is located; and
5. The ICANN region in which the node is located.
The A record returned in the response to such queries is guaranteed
to be unique to the responding node.
Since in this case 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 .../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 .../IN/A and .../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 TTLs in responses from the authoritative 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 use DNS-
specific tools such as dig.
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[monster:~]% dig IDENTITY.L.ROOT-SERVERS.ORG TXT +short
"ytz01.l.root-servers.org" "Toronto" "Ontario" "Canada" "NorthAmerica"
[monster:~]%
[monster:~]% dig IDENTITY.L.ROOT-SERVERS.ORG A +short
67.215.199.91
[monster:~]%
3.5. 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.
[monster:~]% 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"
[monster:~]%
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4. Provisioning of IDENTITY.L.ROOT-SERVERS.ORG
Individual L-Root nodes run a dedicated, separate authority-only DNS
server process which serves the IDENTITY.L.ROOT-SERVERS.ORG zone.
The contents of that zone are unique to every node, and 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,
and hence 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; 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.
The L.ROOT-SERVERS.ORG zone is signed using DNSSEC, and hence secure
responses for BEACON.L.ROOT-SERVERS.ORG and NODES.L.ROOT-SERVERS.ORG
are available. IDENTITY.L.ROOT-SERVERS.ORG is an insecure delegation
from the L.ROOT-SERVERS.ORG zone, however, following the operational
preference to serve static data from each node for that zone, and the
disinclination to distribute key materials and zone signing machinery
to every node.
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5. 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 truely secret, since any service element which
provides service to the Internet can be can never truly be obscured
from 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.
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6. IANA Considerations
This document makes no request of the IANA.
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7. Acknowledgements
The aspects of the L-Root service that were deployed to facilitate
IN-class mapping were discussed and implementated as part of an
informal collaboration with Xun Fan, John Heidemann and Ramesh
Govidan, whose contributions are acknowledged.
Helpful reviews and comments from Gaurab Upadhaya, Hugo Salgado,
Brian Dixon and Bob Harold on earlier versions of this document were
very much appreciated.
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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.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
[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.
8.2. Informative References
[Fan2013] Fan, X., Heidemann, J., and R. Govidan, "Evaluating
Anycast in the Domain Name System", Proceedings of the
IEEE Infocom Turin, Italy, April 2013.
[RFC6304] Abley, J. and W. Maton, "AS112 Nameserver Operations",
RFC 6304, July 2011.
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URIs
[1] <http://www.iata.org/publications/Pages/coding.aspx>
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Appendix A. Editorial Notes
This section (and sub-sections) to be removed prior to publication.
A.1. Change History
00 Initial idea, circulated for the purposes of entertainment.
01 Added some commentary of use-cases of NSID vs various/CH/TXT.
Moved discussion of IN-class queries from the NODES section to the
IDENTITY section. Added a note about DNSSEC for IDENTITY, NODES.
Updated acknowledgements section.
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Author's Address
Joe Abley
ICANN
12025 Waterfront Drive
Suite 300
Los Angeles, CA 90094-2536
USA
Phone: +1 519 670 9327
Email: joe.abley@icann.org
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