dnsop L. Pan
Internet-Draft
Intended status: Informational Y. Fu
Expires: September 28, 2018 CNNIC
March 27, 2018
ISP Location in DNS Queries
draft-pan-dnsop-edns-isp-location-04
Abstract
Nowadays, many Authoritative Nameservers support GeoIP feature, they
guess the user's geolocation by the client subnet of EDNS Client
Subnet (ECS) or by the source IP address of DNS query, return tailor
DNS response based on the user's geolocation. However, ECS raises
some privacy concerns because it leaks client subnet information on
the resolution path to the Authoritative Nameserver.
This document is inspired by EDNS Client Subnet (ECS), describes an
improved solution for GeoIP-enabled Authoritative Nameservers,
defines an EDNS ISP Location (EIL) extension to address the privacy
problem of ECS, tries to find the right balance between privacy
improvement and user experience optimization.
EIL is defined to convey isp location < COUNTRY, AREA, ISP >
information that is relevant to the DNS message. It will directly
provide the same sufficient information for the GeoIP-enabled
Authoritative Nameserver as ECS, to decide the response without
guessing geolocation of the IP address.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 2018.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Path Calculation and Tailored DNS Response . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Problem of ECS . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Client . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Recursive Resolver . . . . . . . . . . . . . . . . . . . 6
4.3. GeoIP-enabled Authoritative Nameserver . . . . . . . . . 7
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. The EIL EDNS0 option . . . . . . . . . . . . . . . . . . 7
6. Protocol Description . . . . . . . . . . . . . . . . . . . . 9
6.1. Originating the Option . . . . . . . . . . . . . . . . . 9
6.1.1. P-Model: Public recursive resolver . . . . . . . . . 9
6.1.2. I-Model: ISP recursive resolver . . . . . . . . . . . 9
6.1.3. L-Model: local forwarding resolver . . . . . . . . . 10
6.2. Generating a Response . . . . . . . . . . . . . . . . . . 10
6.2.1. Whitelist . . . . . . . . . . . . . . . . . . . . . . 10
6.2.2. Authoritative Nameserver . . . . . . . . . . . . . . 10
6.2.3. Intermediate Nameserver . . . . . . . . . . . . . . . 11
6.3. Handling EIL Responses and Caching . . . . . . . . . . . 11
6.3.1. Answering from Cache . . . . . . . . . . . . . . . . 11
6.3.2. Delegations and Negative Answers . . . . . . . . . . 12
6.4. Deploy . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4.1. Transitivity . . . . . . . . . . . . . . . . . . . . 12
6.4.2. Compatibility with non-EDNS and ECS . . . . . . . . . 12
6.4.3. Support ECS and EIL at the same time . . . . . . . . 13
6.5. Why not use AS number to build EIL . . . . . . . . . . . 14
7. Benefit and Cost . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Client . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.2. Recursive Resolver . . . . . . . . . . . . . . . . . . . 15
7.3. GeoIP-enabled Authoritative Nameserver . . . . . . . . . 16
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8.1. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.3. Target Censorship . . . . . . . . . . . . . . . . . . . . 17
8.4. DDoS . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
11. Appendix A. GeoIP-enabled Authoritative Nameservers Example . 17
11.1. BIND-GeoIP . . . . . . . . . . . . . . . . . . . . . . . 18
11.2. PowerDNS-GeoIP . . . . . . . . . . . . . . . . . . . . . 18
11.3. Amazon-Geolocation-Routing . . . . . . . . . . . . . . . 19
11.4. DYN-Traffic-Director-ECS . . . . . . . . . . . . . . . . 20
11.5. gdnsd-GeoIP . . . . . . . . . . . . . . . . . . . . . . 20
11.6. Windows-Server-GeoLocation . . . . . . . . . . . . . . . 20
12. Appendix B. EIL Example . . . . . . . . . . . . . . . . . . . 20
12.1. P-Model . . . . . . . . . . . . . . . . . . . . . . . . 20
12.2. I-Model . . . . . . . . . . . . . . . . . . . . . . . . 21
12.3. L-Model . . . . . . . . . . . . . . . . . . . . . . . . 21
13. Appendix C. Frequent GeoIP-enabled Authoritative Nameserver's
Response Accuracy Problem . . . . . . . . . . . . . . . . . . 21
13.1. Public Recursive Resolver with non-ECS Authoritative
Nameserver . . . . . . . . . . . . . . . . . . . . . . . 21
13.2. IP2Geo Database Quality . . . . . . . . . . . . . . . . 22
13.3. Unstable ISP Network Topology . . . . . . . . . . . . . 22
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
14.1. Normative References . . . . . . . . . . . . . . . . . . 22
14.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Nowadays, many authoritative nameservers support GeoIP feature, such
as [BIND-GeoIP], [PowerDNS-GeoIP], [Amazon-Geolocation-Routing],
[DYN-Traffic-Director-ECS], [gdnsd-GeoIP],
[Windows-Server-GeoLocation] (More details are given in Appendix A).
These geographically aware authoritative nameservers guess the user's
geolocation by the client subnet of ECS or by the source IP address
of DNS query, return tailor DNS response based on the user's
geolocation.
ECS is an EDNS0 [RFC6891] option, described in [RFC7871], carries
client subnet information in DNS queries for authoritative
nameserver. Compared to source IP address of DNS query, ECS will
help authoritative nameserver to guess the client's location more
precisely because of the DNS forwarding query structure.
GeoIP-enabled authoritative nameservers use ECS for user geolocation
detecting. However, ECS raises some privacy concerns because it
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leaks client subnet information on the resolution path to the
authoritative nameserver.
This document describes an improved solution for GeoIP-enabled
authoritative nameserver, defines an EDNS ISP Location (EIL)
extension to address the privacy problem of ECS, tries to find the
right balance between privacy improvement and user experience
optimization.
EIL is defined to convey isp location < COUNTRY, AREA, ISP >
information that is relevant to the DNS message. It will directly
provide the same sufficient information for the GeoIP-enabled
authoritative nameserver as ECS, to decide the response without
guessing geolocation of the IP address.
EIL is intended for those local forwarding resolvers, recursive
resolvers and authoritative nameservers that would benefit from the
extension and not for general purpose deployment. It could be
applied for tailor DNS response like ECS scenario. EIL can safely be
ignored by servers that choose not to implement or enable it.
1.1. Path Calculation and Tailored DNS Response
Separate the consideration of path calculation (data provider) and
tailored DNS response (authoritative nameserver).
Data providers make path calculations to optimize content delivery on
the Internet based on the network topology, considering many factors
such as IP, RIPs, FIBs, AS Path hops, system load, content
availability, path latency, etc. Note that, data providers have the
full details of the clients, they can make any complex path
calculations without ECS and EIL.
authoritative nameservers configure tailored DNS response based on
the result of path calculations, allocate IP addresses to different
datacenters, each IP address serves many client subnets. Usually,
users from the same < COUNTRY, AREA, ISP > isp location are allocated
to the same datacenter, the same best "network topologically close"
datacenter. For example, client IP addresses from < China, Beijing,
Telecom > are allocated to DataCenter-1, client IP addresses from <
China, Beijing, Unicom > are allocated to DataCenter-2, etc. Above
is the GeoIP-based Tailored DNS Response.
Therefore, if the GeoIP-enabled authoritative nameservers support
ECS, they can use the client subnet information of ECS instead of
resolver's address for geolocation detecting. Alternative, the
GeoIP-enabled authoritative nameservers can directly use the <
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COUNTRY, AREA, ISP > information of EIL without geolocation
detecting.
Again, we emphasize that tailored DNS response does not affect path
calculation. Data Providers can make path calculations based on
network topology, decide network topological close datacenter for
each IP address. authoritative nameservers allocate tailored DNS
response to each IP address based on the "network topological close"
result of path calculations. EIL tell authoritative nameserver like
that, "I want to know what is best IP address for clients from <
China, Beijing, Telecom > at network topology path calculations
result", but not "I want to know what is the nearest IP address for
clients from < China, Beijing, Telecom > at physical topology path
calculations result".
EIL is satisfied if authoritative nameservers aggregate the IP
addresses from the same < COUNTRY, AREA, ISP > isp location to visit
the same datacenters, we call that GeoIP-based tailored DNS
responses, and these tailored responses have the best "network
topological close" distance to the users which are generated from
network topology path calculations result.
ECS is satisfied if authoritative nameservers make tailored DNS
response down to subnet precise level. For example, (subnet-1, ...,
subnet-100) are from the same < COUNTRY, AREA, ISP > isp location,
Data Provider applies (subnet-1, ..., subnet-50) visit DataCenter-1,
(subnet-51, ..., subnet-100) visit DataCenter-2.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when they appear in ALL CAPS. When these words are not in
ALL CAPS (such as "should" or "Should"), they have their usual
English meanings, and are not to be interpreted as [RFC2119]
keywords.
3. Terminology
Basic terms used in this specification are defined in the documents
[RFC1034], [RFC1035], [RFC7719] and [RFC7871].
EIL: EDNS ISP Location.
ECS: EDNS Client Subnet, described in [RFC7871].
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Local Forwarding Resolver: forwarding resolver is described in
[RFC7871]. It is the first forwarding resolver which receives DNS
queries from stub resolver, usually deployed nearby the first-hop
router such as public Wi-Fi hotspot routers and home routers.
Recursive Resolver: described in [RFC7871]. It is the last-hop
before authoritative nameserver in the DNS query path.
Intermediate Nameserver: described in [RFC7871]. Any nameserver in
between the stub resolver and the authoritative nameserver, such as a
recursive resolver or a Forwarding Resolver.
Intermediate Forwarding Resolver: Any Forwarding Resolver in between
the local forwarding resolver and recursive resolver.
authoritative nameserver: described in [RFC7719] and [RFC2182]. It
is a server that knows the content of a DNS zone from local
knowledge, and thus can answer queries about that zone without
needing to query other servers.
4. Problem of ECS
As mentioned in [RFC7871]'s abstract section, since ECS has some
known operational and privacy shortcomings, a revision will be worked
through the IETF for improvement.
4.1. Client
Common users have little power to defense passive monitoring,
expecially in the plain-text traffic.
ECS's client subnet leakage has rise some user privacy concerns.
4.2. Recursive Resolver
Recursive Resolver must deal with ECS's cache problem, such as low
cache hitrate, rise response time, redundant cache size, etc.
Mukund Sivaraman described some scenarios in [CLIENT-SUBNET-BIS].
ECS is precise because it is based on client subnet. But IPv6
addresses will boom, we can foresee it to increase more burden on
global recursive resolvers.
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4.3. GeoIP-enabled Authoritative Nameserver
Resolver's IP can on behalf of many client subnets if they are
topological close. But this scenario has been varied by public
recursive resolver. ECS push client subnets to authoritative
nameserver, wants to solve the "public recursive resolver's IP is
topological far from client subnet" problem.
However, ECS rises GeoIP-enabled authoritative nameserver's
dependence on IP2Geo database quality.
Many GeoIP-enabled authoritative nameserver, most of the time, use <
COUNTRY, AREA, ISP > information to decide the tailored response.
Every GeoIP-enabled authoritative nameserver must operate IP2Geo
database carefully and catch up with topology change. The work is
inevitable, but ECS aggravate this, because the number of client
subnets is far greater than the number of recursive resolvers.
GeoIP-enabled authoritative nameserver needs a more precise IP2Geo
database, updates it more frequent than before, to catch up with the
huge client subnet network topology, but not the dns resolver's IP
network topology. Every GeoIP-enabled authoritative nameserver
should cost more on IP2Geo database.
5. Overview
EIL is an EDNS0 option to allow local forwarding resolvers and
recursive resolvers, if they are willing, to forward details about
the isp location of client when talking to other nameservers. EIL
can be added in queries sent by local forwarding resolvers or
recursive resolvers in a way that is transparent to Stub Resolvers
and end users.
Like ECS, authoritative nameservers could provide a better answer by
using precise isp location in EIL. Intermediate Nameservers could
send EIL query and cache the EIL response. This document also
provides a mechanism to signal Intermediate Nameservers that they do
not want EIL treatment for specific queries.
EIL is only defined for the Internet (IN) DNS class.
5.1. The EIL EDNS0 option
The EIL is an EDNS0 option to include the isp location of client in
DNS messages.
It is 16 octets which is structured as follows:
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+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | COUNTRY |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | AREA |
| |
| |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
12: | ISP |
| |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Total: 16 octets.
o OPTION-CODE, 2 octets, defined in [RFC6891]. EDNS option code
should be assigned by the IANA.
o OPTION-LENGTH, 2 octets, defined in [RFC6891], contains the length
of the payload (everything after OPTION-LENGTH) in octets.
o COUNTRY, 2 octets, uppercase, defined in [ISO3166], indicates the
country information of the client's IP. For example, China's
COUNTRY is CN.
o AREA, 6 octets, uppercase, defined in [ISO3166] country
subdivision code, indicates the area information of the client's
IP. For example, The AREA of Fujian Province in China is 35.
o ISP, 4 octets, uppercase, indicates the ISP information of the
client's IP, using shortcut names. ISP shortcut names are unique
within the context of the COUNTRY. For example, the shortcut name
of China Telecommunications Corporation is TEL, the shortcut name
of China United Network Communications is UNI, the shortcut name
of China Mobile is MOB, etc.
All fields are in network byte order ("big-endian", per [RFC1700],
Data Notation).
The aim to use short names in the fields is to limit the data size of
EIL, decrease the DDoS risk.
The null value 0x20 signifies that the field is unknown. If all
fields in EIL are set to null value, it means that client doesn't
want to use EIL.
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authoritative nameservers can send EIL response with the * value 0x2A
in AREA field or ISP field (not COUNTRY field), which signifies that
the field is wildcard match. For example, < CN, *, TEL > indicates
"all area in China, Telecom ISP".
Example code is at [DNS-TEST-EIL] .
6. Protocol Description
6.1. Originating the Option
The EIL can be initialized by Public recursive resolver, ISP
recursive resolver, or local forwarding resolver.
Examples are given in Appendix B.
6.1.1. P-Model: Public recursive resolver
Public recursive resolvers are not close to many users because the
service providers couldn't deploy servers in every country and every
ISP's network, which will affect the response accuracy of
authoritative nameservers. To encounter this problem, ECS shifts the
client subnet information to authoritative nameserver, but rises user
privacy concerns.
Therefore, to keep balance between precise and privacy, when a Public
recursive resolver receives a DNS query, it can guess isp location of
client's IP and generate the EIL OPT data, then send EIL query to the
authoritative nameserver. This will move the "guess location of
client's IP" work from authoritative nameserver back to Public
recursive resolver, lighten the burden of authoritative nameserver,
but increase DDoS risk on Public recursive resolver.
In order to improve the user's privacy, if a recursive resolver
receives a DNS query with ECS, it can guess the isp location of
SOURCE-PREFIX from the ECS OPT data, and make a new DNS query with
EIL, then send the query to authoritative nameserver which supports
EIL.
P-model is the most recommended and close to the ECS.
6.1.2. I-Model: ISP recursive resolver
ISP recursive resolver only serves its customers, each of whom has a
static isp location. ISP recursive resolver can add EIL transparent
to end user, and then authoritative nameserver doesn't need to "guess
location of client's IP".
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EIL will be benefit if the authoritative nameserver could not find
the approximate isp location of ISP recursive resolver, which is
crucial to DNS response accuracy in ECS.
6.1.3. L-Model: local forwarding resolver
local forwarding resolver is usually on the first-hop router, such as
public Wi-Fi hotspot routers and Cisco/Linksys/Netgear/TP-LINK home
routers.
When a local forwarding resolver that implements EIL receives a DNS
query from an end user, it surely can know about the isp location of
client's IP, and generate the EIL OPT data, then send the EIL query
to the intermediate recursive resolver. Intermediate recursive
resolver sends the EIL query to the authoritative nameserver.
In this scenario, both Public recursive resolver and authoritative
nameserver don't need to "guess location of client's IP", because the
local forwarding resolver supplies the isp location precisely. That
is, EIL can reduce dependence on the IP geolocation database quality,
which is crucial to DNS response accuracy in ECS.
If a local forwarding resolver had sent a query with EIL, and
receives a REFUSE response, it MUST regenerate a query with no EIL.
6.2. Generating a Response
6.2.1. Whitelist
EIL contains a whitelist for COUNTRY, AREA and ISP, which can be
discussed and maintained by the DNSOP working group. authoritative
nameservers that supporting EIL must only response the EIL queries
matched the whitelist. recursive resolver that supporting EIL must
only cache the EIL responses matched the whitelist.
6.2.2. Authoritative Nameserver
Using the isp location specified in the EIL option of DNS query, an
authoritative nameserver can generate a tailored response.
authoritative nameservers that have not implemented or enabled
support for the EIL ought to safely ignore it within incoming
queries, response the query as a normal case without EDNS0 option.
Such a server MUST NOT include an EIL option within replies to
indicate lack of support for it.
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An authoritative nameserver that has implemented this protocol and
receives an EIL option MUST include an EIL option in its response to
indicate that it SHOULD be cached accordingly.
An authoritative nameserver will return a more appropriate tailored
response for the query with an EIL option containing more precisely
AREA.
6.2.3. Intermediate Nameserver
Like ECS, Intermediate Nameserver passes a DNS response with an EIL
option to its client when the client indicates support EIL.
If an Intermediate Nameserver receives a response that has a larger
area than the AREA provided in its query, it SHOULD still provide the
result as the answer to the triggering client request even if the
client is in a smaller area.
6.3. Handling EIL Responses and Caching
If an Intermediate Nameserver had sent a query with EIL, and receives
a NOERROR response without EIL option, it SHOULD treat this answer as
suitable for all clients.
Other handling considerations are similar with ECS [RFC7871], SECTION
7.3.
In the cache, all resource records in the Answer section MUST be tied
to the isp location specified in the response. The Answer section is
valid for all areas which the EIL option covered. For example, an
EIL option < CN, 35, TEL > covers all 9 Cities in Fujian Province of
China Telecommunications ISP.
Same with ECS, The Additional and Authority sections are excluded.
Enabling support for EIL in an Intermediate Nameserver will increase
the size of the cache, and prevent "client subnet leak" privacy
concern of ECS.
6.3.1. Answering from Cache
Cache lookups are first done as usual for a DNS query, using the
query tuple of < name, type, class >. Then, the appropriate RRset
MUST be chosen based on the isp location matching.
If there was an EIL option, the Intermediate Nameserver will lookup
for < same COUNTRY, same ISP, same AREA > of the same query tuple in
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the cache. Otherwise, try to find < same COUNTRY, same ISP, same
AREA > of the same query tuple in the cache.
If no EIL option was provided, the safest choice of the Intermediate
Nameserver is dealing the query as a normal case without EDNS0
option.
If no EIL option was provided, but the Intermediate Nameserver want
to be more aggressive, it can guess the isp location from the source
IP of the query, then respond as if there was an EIL option with the
guessed information. Users can be benefit when the Intermediate
Nameserver has a more precise IP location database than the
authoritative nameserver, especially in global public DNS service
like GoogleDNS(8.8.8.8).
If no matching is found, the Intermediate Nameserver MUST perform
resolution as usual.
6.3.2. Delegations and Negative Answers
EIL's delegation case is similar with ECS, Additional and Authority
Sections SHOULD ignore EIL.
For negative answers, authoritative nameservers return traditional
negative answers without EIL.
6.4. Deploy
6.4.1. Transitivity
EIL's transitivity concerns are similar with ECS.
Name servers should only enable EIL where it is expected to benefit
the end users, such as dealing with some latency-sensitive CDN domain
queries in a complex network environment.
6.4.2. Compatibility with non-EDNS and ECS
For realworld compatibility, EIL is designed as an additional feature
to ECS. If a nameserver supports EIL, it must support ECS first. So
there are three scenarios: non-EDNS, ECS but non-EIL, ECS and EIL.
o GeoIP-enabled authoritative nameservers map ECS's client subnet
into EIL's geolocation to get tailor response, they can simply add
EIL support. Some realtime client subnet sensitive CDN domains,
such as Akamai, they may not support GeoIP feature and EIL.
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o EIL-enabled recursive resolvers only send EIL queries to EIL-
enabled authoritative nameservers. At the same time, they can
also send ECS queries.
The indicator that authoritative nameservers used to generate tailor
response is showed as follows:
+-------------------------+-----------------+------------------------+----------------------------------------------+
| | AUTH (non-EDNS) | AUTH (ECS but non-EIL) | AUTH (ECS and EIL) |
+-------------------------+-----------------+------------------------+----------------------------------------------+
| RECUR (non-EDNS) | Resolver's IP | Resolver's IP | Resolver's IP |
+-------------------------+-----------------+------------------------+----------------------------------------------+
| RECUR (ECS but non-EIL) | Resolver's IP | Client Subnet | Client Subnet |
+-------------------------+-----------------+------------------------+----------------------------------------------+
| RECUR (ECS and EIL) | Resolver's IP | Client Subnet | Client Subnet or EIL's < COUNTRY, AREA, ISP >|
+-------------------------+-----------------+------------------------+----------------------------------------------+
6.4.3. Support ECS and EIL at the same time
Name servers can support ECS and EIL at the same time. ECS and EIL
can't be both initiated at the same DNS packet. It is better for
user privacy if name servers initiate the EIL query prior to the ECS
query.
If authoritative nameservers support both ECS and EIL, recursive
resolvers can cache both ECS response and EIL response, there are
some choices for recursive resolvers when they receive DNS queries.
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Receive EIL query:
Search in EIL cache.
If cache is matched, return EIL response.
Otherwise, send EIL query to authoritative nameserver.
Receive ECS query:
Search in ECS cache.
If cache is matched, return ECS response.
Otherwise, send ECS query to authoritative nameserver.
Receive DNS query without EDNS option:
Search in ECS cache.
If cache is matched, return ECS response.
Otherwise,
Guess the isp location information of the client's IP,
build EIL option for the query packet.
Search in EIL cache.
If cache is matched, return EIL response.
Otherwise, send EIL query to authoritative nameserver.
Receive DNS query with not-ECS/not-EIL option:
Search in not-EDNS cache.
If cache is matched, return response.
Otherwise, send the DNS query to authoritative nameserver.
Receive ECS query, improve user privacy:
Guess the isp location information of the client's IP,
build EIL option for the query packet.
Search in EIL cache.
If cache is matched, return EIL response RR with origin ECS option.
Otherwise, send EIL query to authoritative nameserver.
6.5. Why not use AS number to build EIL
AS number is not an ideal object to balance between response accuracy
and user privacy, for example:
o AS24151 can directly guide to China Internet Network Infomation
Center, it is not good for user privacy.
o AS4134 contains a huge amount of IP prefixes whose geolocation
covers from South China to North China, AS number can not afford
the response accuracy consideration.
o < COUNTRY-CODE, AREA-CODE, AS-NUMBER > may be a considerable
trade-off choice on public recursive resolver, but inconvenience
on local forwarding resolver.
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7. Benefit and Cost
7.1. Client
EIL is transparent to client.
EIL is to help mitigate client subnet leakage on the resolution path,
without sensitive identity information.
7.2. Recursive Resolver
ECS sends the query with client subnet, which means that recursive
resolvers have to send a new query to authoritative nameservers with
client_subnet_b, even it has known the response about topological
close client_subnet_a. In fact, thousands of subnets visit only a
few servers, there are many redundacy queries, the recursive's cache
hitrate is low.
Because of ECS's low cache hitrate, recursive servers's ECS tailored
response latency will be longer, the average of response time will
rise with the redundacy queries rate from recursive resolvers to
authoritative nameservers.
Recursive's ECS cache size grows up with the number of client
subnets.
To sum it up, above problems all rise with the client subnet amount,
especially when IPv6 addresses boom. Extend the subnet range in the
ECS response may be mitigating, but not work for wide range client
subnets. Recursive can make some guess optimization, if it has known
response for client_subnet_a, then guess to return the same response
for toplogical close client_subnet_b without send the redundancy
query.
Therefore, if the ECS revision wants to make more effective client
subnets aggregation for recursive resolver, then EIL can be an
considerable choice. EIL wants to summary toplogical close client
subnets into < COUNTRY, AREA, ISP > for GeoIP-enabled authoritative
nameserver. With EIL response cache, recursive resolvers can
directly response for many ECS client subnets queries, which will
rise cache hitrate and reduce response latency. The cache size of
EIL is related to the row count in the < COUNTRY, AREA, ISP > isp
location whitelist. Therefore, under IPv6 environment, the cache
size of EIL will be much smaller than ECS.
Note that, the EIL's IP2Geo mapping work will make recursive resolver
to cost more cpu.
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7.3. GeoIP-enabled Authoritative Nameserver
Client subnet is the best factor if the company has good network
topology monitor ability, offen is for big company. However, for
many authoritative servers that only deployed GeoDNS, the accuracy
limitation is commonly because of the IP2Geo database quality, and
the small ISPs change to another next-hop big ISP suddenly.
For the GeoIP-enabled authoritative nameserver, the response
accurancy depends on the IP geolocation database quality. If
authoritative nameserver can not find approximate isp location of
ECS's client subnet, they can not return best tailored response.
Even though GeoIP-enabled authoritative nameservers know about the
precise isp location of ECS's client subnet, they may not know about
the latest toplogical path change of the isp to update the tailored
response in time. In the case of "small ISP -> big ISP (change
frequency) -> ... -> website", both small ISP's client ip/resolver ip
is not good factor for GeoDNS. Big companies work hard to catch up
with the client ip's connect topology change, and adjust their
authoritative nameservers' tailored response, but smaller companies
only deploy IP2Geo may not afford.
EIL wants to give downstream a chance to tell authoritative
nameserver its best path quickly and proactively, help to rise the
response accuracy, avoid cross-isp visit, save IP transit cost for
Data Provider. EIL directly provide sufficient information for the
GeoIP-enabled authoritative nameserver. Compared to ECS, EIL can
reduce GeoIP-enabled authoritative nameserver's dependence on the IP
geolocation database quality.
8. Security Considerations
8.1. DNSSEC
EIL is not signed.
8.2. Privacy
The biggest privacy concern on ECS is that client subnet information
is personally identifiable. The more domains publish their zones on
a third-party authoritative nameserver, the more end user privacy
information can be gathered by the authoritative nameserver according
to the ECS queries.
EIL is to improve user privacy which is inspired by ECS, prevented
leaks in the client subnet information.
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Like ECS, EIL will leak the global zonefile configurations of the
authoritative nameservers more easily than normal case.
8.3. Target Censorship
DNS traffic is plain text by default. It is easily to be blocked or
poisoned by internet target censorship. To bypass the censorship, it
is better to encrypt the DNS traffic or use some proxy tunnel.
EIL's isp location information covers bigger area than ECS's client
subnet information. Therefore, compared to ECS in plain text
condition, EIL is weaker at blocking record attack, but stronger at
targeted DNS poisoning attack.
8.4. DDoS
To migrate the DDoS problem:
o If an Authority Server receives a DNS query with unknown data in
EIL option, it SHOULD return the default response whose EIL option
with null value.
o Nameservers OPTIONAL only implement EIL when the query is from a
TCP connection.
More migration techniques described in [RFC7871], Section 11.3.
9. IANA Considerations
This document defines EIL, need request IANA to assign a new EDNS0
option code to EIL.
10. Acknowledgements
EIL is inspired by ECS, the authors especially thanks to C.
Contavalli, W. van der Gaast, D. Lawrence, and W. Kumari.
Thanks comments for Barry Raveendran Greene, Paul Vixie, Petr
Špaček, Brian Hartvigsen, Ask Bjoern Hansen, Dave Lawrence.
Thanks a lot to all in the DNSOP, DNSPRIV mailing list.
11. Appendix A. GeoIP-enabled Authoritative Nameservers Example
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11.1. BIND-GeoIP
As described in [BIND-GeoIP], BIND 9.10 is able to use data from
MaxMind GeoIP databases to achieve restrictions based on the
(presumed) geographic location of that address. The ACL itself is
still address-based, but the GeoIP-based specification mechanisms can
easily populate an ACL with addresses in a certain geographic
location.
acl "example" {
geoip country US;
geoip region CA;
geoip city "Redwood City"; /* names, etc., must be quoted if they contain spaces */
};
11.2. PowerDNS-GeoIP
As described in [PowerDNS-GeoIP], PowerDNS supports many geolocation
placeholders, such as %co = 3-letter country, %cn = continent, %re =
region, %ci = city.
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domains:
- domain: geo.example.com
ttl: 30
records:
geo.example.com:
- soa: ns1.example.com hostmaster.example.com 2014090125 7200 3600 1209600 3600
- ns:
content: ns1.example.com
ttl: 600
- ns: ns2.example.com
- mx: 10 mx.example.com
fin.eu.service.geo.example.com:
- a: 192.0.2.2
- txt: hello world
- aaaa: 2001:DB8::12:34DE:3
# this will result first record being handed out 30% of time
swe.eu.service.geo.example.com:
- a:
content: 192.0.2.3
weight: 50
- a: 192.0.2.4
services:
# syntax 1
service.geo.example.com: '%co.%cn.service.geo.example.com'
# syntax 2
service.geo.example.com: [ '%co.%cn.service.geo.example.com', '%cn.service.geo.example.com']
# alternative syntax
services:
service.geo.example.com:
default: [ '%co.%cn.service.geo.example.com', '%cn.service.geo.example.com' ]
10.0.0.0/8: 'internal.service.geo.example.com'
11.3. Amazon-Geolocation-Routing
As described in [Amazon-Geolocation-Routing], Amazon Route 53 lets
you choose the resources that serve your traffic based on the
geographic location of your users, meaning the location that DNS
queries originate from. It allows you to route some queries for a
continent to one resource and to route queries for selected countries
on that continent to a different resource.
When a browser or other viewer uses a DNS resolver that does support
edns-client-subnet, the DNS resolver sends Amazon Route 53 a
truncated version of the user's IP address. Amazon Route 53
determines the location of the user based on the truncated IP address
rather than the source IP address of the DNS resolver; this typically
provides a more accurate estimate of the user's location. Amazon
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Route 53 then responds to geolocation queries with the DNS record for
the user's location.
11.4. DYN-Traffic-Director-ECS
As described in <DYN-Traffic-Director-Geographic-Groups> and
[DYN-Traffic-Director-ECS], Dyn provides the ability to control DNS
responses on a granular/customized geographical rule set. Part of
the rulesets will be the identification of the global regions,
countries, or states and provinces that use a specific DNS server
group. DYN uses the ECS information for the geolocation lookup.
Once a geolocation is found and a response is selected, it will
provide a DNS response back to the source IP address.
11.5. gdnsd-GeoIP
As described in [gdnsd-GeoIP], gdnsd uses MaxMind's GeoIP binary
databases to map address and CNAME results based on geography and
monitored service availability. gdnsd supports geolocation codes,
such as continent, country, region/subdivision, city.
11.6. Windows-Server-GeoLocation
As described in [Windows-Server-GeoLocation], Windows server can be
configured DNS Policy to respond to DNS client queries based on the
geographical location of both the client and the resource to which
the client is attempting to connect, providing the client with the IP
address of the closest resource.
12. Appendix B. EIL Example
Authoritative nameserver of www.example.com has enabled EIL.
Stub DNS query A resource record of www.example.com .
12.1. P-Model
Stub DNS
-> local forwarding resolver (61.48.7.2)
-> Public Forwarding Resolver(AliDNS, 223.5.5.5)
-> Public recursive resolver(AliDNS, 202.108.250.231)
-> authoritative nameserver
Public Forwarding Resolver 223.5.5.5 could enable EIL and generate
the EIL OPT data < CN, 11, UNI > based on 61.48.7.2.
P-Model will not leak client subnet to authoritative nameserver.
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12.2. I-Model
Stub DNS
-> local forwarding resolver
-> ISP Forwarding Resolver(202.106.196.115)
-> ISP recursive resolver(61.135.23.92)
-> authoritative nameserver
ISP recursive resolver 61.135.23.92 could enable EIL and generate the
EIL OPT data < CN, 11, UNI > based on 61.135.23.92.
If authoritative nameserver doesn't know much about 61.135.23.92, EIL
will be helpful.
ISP recursive resolver generates static EIL query, simply manages
response cache as tranditionl non-ECS/non-EIL scenario.
EIL helps ISP recursive resolver to give upstream an explicit correct
isp location information.
12.3. L-Model
Stub DNS
-> Local Fowarding Resolver(58.60.109.234)
-> ...
-> authoritative nameserver
Local Fowarding Resolver 58.60.109.234 could enable EIL and generate
the option data is < CN, 44, TEL > based on 58.60.109.234.
L-Model can give the most precisely isp location information for DNS
resolution.
13. Appendix C. Frequent GeoIP-enabled Authoritative Nameserver's
Response Accuracy Problem
13.1. Public Recursive Resolver with non-ECS Authoritative Nameserver
If authoritative nameserver doesn't support ECS, the clients that use
public recursive resolver(such as 8.8.8.8) may receive disaster
latency IP.
In this scenario, we must pray that public recursive resolver's IP is
topological close to client's IP.
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13.2. IP2Geo Database Quality
If authoritative nameserver's IP2Geo database misidentify client IP's
information, then the client may be assigned to some high letency
cross-isp IP address.
With EIL, public recursive resolver and ISP recursive resolver can
help to give more precise information for GeoIP-enabled authoritative
nameservers.
13.3. Unstable ISP Network Topology
Some small ISPs may change their upstreams frequently. Authoritative
nameservers offen can not catch up the variation in time.
EIL gives downstream a chance to proactively tell authoritative
nameservers the latest best topological close response itself wants
now. Downstream can assure itself has got explicit tailored response
with EIL.
For example, 218.247.200.100's isp location information is < China,
Beijing, PengBoShi >. In I-Model, PengBoShi's resolver can send EIL
< CN, 11, TEL > to authoritative nameservers, indicates that the best
topological close response forclient 218.247.200.100 is from China
Beijing Telecom.
14. References
14.1. Normative References
[RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities",
RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, November 1987.
[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2182] ELZ, R., Bush, R., Bradner, S., and M. Patton, "Selection
and Operation of Secondary DNS Servers", RFC 2182, July
1997.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", RFC 6891, April 2013.
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[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, December 2015.
[RFC7871] Contavalli, C., van der Gasst, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871, May
2016.
14.2. Informative References
[Amazon-Geolocation-Routing]
Amazon, "Amazon Route 53: Geolocation Routing",
<http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/
routing-policy.html#routing-policy-geo>.
[BIND-GeoIP]
ISC BIND, "Using the GeoIP Features in BIND 9.10",
<https://kb.isc.org/article/AA-01149/0>.
[CLIENT-SUBNET-BIS]
Sivaraman, Mukund., "CLIENT-SUBNET bis appetite?",
<https://www.ietf.org/mail-archive/web/dnsop/current/
msg21616.html>.
[DNS-TEST-EIL]
Pan, Lanlan., "dns_test_eil", <https://github.com/abbypan/
dns_test_eil>.
[DYN-Traffic-Director-ECS]
DYN, "What happens when a DNS query for a Traffic Director
instance is received with ECS information",
<https://help.dyn.com/edns-client-subnet-faq-info/#q6>.
[DYN-Traffic-Director-Geographic-Groups]
DYN, "Predefined Geographic Groups of Traffic Director",
<https://help.dyn.com/traffic-director-predefined-
geographic-regions/>.
[gdnsd-GeoIP]
gdnsd, "GdnsdPluginGeoip",
<https://github.com/gdnsd/gdnsd/wiki/GdnsdPluginGeoip>.
[ISO3166] ISO 3166, "Country Codes",
<http://www.iso.org/iso/country_codes>.
[PowerDNS-GeoIP]
PowerDNS, "PowerDNS GeoIP backend",
<https://doc.powerdns.com/md/authoritative/backend-
geoip/>.
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[Windows-Server-GeoLocation]
Microsoft, "Use DNS Policy for Geo-Location Based Traffic
Management with Primary Servers",
<https://docs.microsoft.com/en-us/windows-
server/networking/dns/deploy/primary-geo-location>.
Authors' Addresses
Lanlan Pan
Beijing
China
Email: abbypan@gmail.com
URI: https://github.com/abbypan
Yu Fu
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
China
Email: fuyu@cnnic.cn
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