wdiff draft-ietf-dnsop-edns-client-subnet-00.txt draft-ietf-dnsop-edns-client-subnet-01.txt

dnsop C. Contavalli
Internet-Draft W. van der Gaast
Intended status: Informational Google
Expires: May 19, November 27, 2015 D. Lawrence
Akamai Technologies
W. Kumari
Google
November 15, 2014
May 26, 2015

Client Subnet in DNS Requests
draft-ietf-dnsop-edns-client-subnet-00 Querys
draft-ietf-dnsop-edns-client-subnet-01

Abstract

This draft defines an EDNS0 extension to carry information about the
network that originated a DNS query, and the network for which the
subsequent reply response can be cached.

IESG Note

[RFC Editor: Please remove this note prior to publication ]

This informational document describes an existing, implemented and
deployed system. A subset of the operators using this is at
http://www.afasterinternet.com/participants.htm . The authors believe
that it is better to document this system (even if not everyone
agrees with the concept) than leave it undocumented and proprietary.

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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 May 19, November 27, 2015.

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
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5
5. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Protocol Description . . . . . . . . . . . . . . . . . . . . 7
6.1. Originating the Option . . . . . . . . . . . . . . . . . 7
6.1.1. Recursive Resolvers . . . . . . . . . . . . . . . . . 7
6.1.2. Stub Resolvers . . . . . . . . . . . . . . . . . . . 8
6.1.3. Forwarders . . . . . . . . . . . . . . . . . . . . . 9
6.2. Generating a Response . . . . . . . . . . . . . . . . . . 8 9
6.2.1. Authoritative Nameserver . . . . . . . . . . . . . . 9
6.2.2. Intermediate Nameserver . . . . . . . . . . . . . . . 10
6.3. Handling edns-client-subnet Replies ECS Responses and Caching . . . . . 9 . . . . . . 11
6.3.1. Caching the Response . . . . . . . . . . . . . . . . 11
6.3.2. Answering from Cache . . . . . . . . . . . . . . . . 12
6.4. Delegations and Negative Answers . . . . . . . . . . . . 13
6.5. Transitivity . . . . . . . . . . . . . . . . . . . . . . 11 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 14
8. DNSSEC Considerations . . . . . . . . . . . . . . . . . . . . 12 14
9. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 12 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 15
10.1. Privacy . . . . . . . . . . . . . . . . . . . . . . . . 13 15
10.2. Birthday Attacks . . . . . . . . . . . . . . . . . . . . 14 16
10.3. Cache Pollution . . . . . . . . . . . . . . . . . . . . 14 17
11. Sending the Option . . . . . . . . . . . . . . . . . . . . . 16 18
11.1. Probing . . . . . . . . . . . . . . . . . . . . . . . . 16 18
11.2. Whitelist . . . . . . . . . . . . . . . . . . . . . . . 16 19
12. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 19
13. Contributing Authors . . . . . . . . . . . . . . . . . . . . 19 21
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 21
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 22
15.1. Normative References . . . . . . . . . . . . . . . . . . 19 22
15.2. Informative References . . . . . . . . . . . . . . . . . 20 23
15.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 20 23
Appendix A. Document History . . . . . . . . . . . . . . . . . . 20 23
A.1. -00 . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 24
A.2. -01 . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 25
A.3. -02 . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
A.4. -03* . . . . . . . . . . . . . . . . . . . . . . . . . . 22 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 26

1. Introduction

Many Authoritative Nameservers today return different replies responses based
on the perceived topological location of the user. These servers use
the IP address of the incoming query to identify that location.
Since most queries come from intermediate Recursive Resolvers, the
source address is that of the Recursive Resolver rather than of the
query originator.

Traditionally, and probably still in the majority of instances,
Recursive Resolvers are reasonably close in the network topology topological sense to
the Stub Resolvers or Forwarders that are the source of queries. For
these resolvers, using their own IP address is sufficient for
authority servers that tailor responses based upon location of the
querier.

Increasingly, though, a class of Recursive Resolvers has arisen that
handle query sources that are often not topologically close. The
motivation for a user to configure such a Centralized Resolver varies
but is usually because of some enhanced experience, such as greater
cache security or applying policies regarding where users may
connect. (Although political censorship usually comes to mind here,
the same actions may be used by a parent when setting controls on
where a minor may connect.) Similarly, many ISPs and other
organizations use a Centralized Resolver infrastructure that can be
distant from the clients the resolvers serve. The These cases all lead
to less than optimal replies desirable responses from topology-sensitive
Authoritative Nameservers.

This draft defines an EDNS0 [RFC6891] option to convey network
information that is relevant to the DNS message. It will carry
sufficient network information about the originator for the
Authoritative Nameserver to tailor responses. It will also provide
for the Authoritative Nameserver to indicate the scope of network
addresses for which the tailored answer is intended. This EDNS0
option is intended for those recursive and authority servers that
would benefit from the extension and not for general purpose
deployment. It is completely optional and can safely be ignored by
servers that choose not to implement it or enable it.

This draft also includes guidelines on how to best cache those
results and provides recommendations on when this protocol extension
should be used.

At least a dozen different client and server implementations had been
written based on the original specification, first known as draft-
vandergaast-edns-client-subnet. While they interoperate for the
primary goal, they have varying behaviour around poorly specified
edge cases. Known incompatibilities will be described.

2. Requirements Notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Terminology

ECS EDNS Client Subnet.

Client A Stub Resolver, Forwarder or Recursive Resolver. A client
to a Recursive Resolver or a Forwarder.

Server A Forwarder, Recursive Resolver or Authoritative Nameserver.

Stub Resolver: A simple DNS protocol implementation on the client
side as described in [RFC1034] section 5.3.1. A client to a
Recursive Resolver or a Forwarder.

Authoritative Nameserver: A nameserver that has authority over one
or more DNS zones. These are normally not contacted by Stub
Resolver or end user clients directly but by Recursive Resolvers.
Described in [RFC1035]
chapter Section 6.

Recursive Resolver: A nameserver that is responsible for resolving
domain names for clients by following the domain's delegation
chain. Recursive Resolvers frequently use caches to be able to
respond to client queries quickly. Described in [RFC1035] chapter
Section 7.

Intermediate Nameserver: Any nameserver (possibly a Recursive
Resolver) in between the Stub Resolver and the Authoritative
Nameserver.

Centralized Resolvers: Recursive Resolvers that serve a
topologically diverse network address space.

Optimized Reply:

Tailored Response: A reply response from a nameserver that is optimized customized
for the node that sent the request, normally query, often based on performance (i.e.
lowest latency, least number of hops, topological distance, ...).

Topologically Close: Refers to two hosts being close in terms of
number of hops or time it takes for a packet to travel from one
host to the other. The concept of topological distance is only
loosely related to the concept of geographical distance: two
geographically close hosts can still be very distant from a
topological perspective, and two geographically distant hosts can
be quite close on the network.

4. Overview

The general idea of this document is to provide an EDNS0 option to
allow Recursive Resolvers, if they are willing, to forward details
about the origin network from which a query is coming when talking to
Authoritative
other Nameservers.

The format of this option is described in Section 5, and is meant to
be added in queries sent by Intermediate Nameservers in a way
transparent to Stub Resolvers and end users, as described in
Section 6.1. ECS is only defined for the Internet (IN) DNS class.

As described in Section 6.2, an Authoritative Nameserver could use
this EDNS0 option as a hint to better locate the network of the end
user and provide a better answer.

Its reply response would also contain an edns-client-subnet (ECS) option,
clearly indicating that the server made use of this information, and
that the answer is tied to the network of the client.

As described in Section 6.3, Intermediate Nameservers would use this
information to cache the reply. response.

Some Intermediate Nameservers may also have to be able to forward
edns-client-subnet ECS
queries they receive. This is described in Section 6.4. 6.5.

The mechanisms provided by edns-client-subnet ECS raise various security related
concerns, related to cache growth, the ability to spoof EDNS0
options, and privacy. Section 10 explores various mitigation
techniques.

The expectation, however, is that this option will only be used by
Recursive Resolvers and Authoritative Nameservers that incur
geolocation issues.

Most Recursive Resolvers, Authoritative Nameservers and Stub
Resolvers will never know about this option, and will continue
working as they had been.

Failure to support this option or its improper handling will, at
worst, cause suboptimal identification of client location, which is a
common occurrence in current content delivery network (CDN) setups
and not a cause of concern. setups.

Section 6.1 also provides a mechanism for Stub Resolvers to signal
Recursive Resolvers that they do not want edns-client-subnet ECS treatment for specific requests.
queries.

Additionally, operators of Intermediate Nameservers with edns-client-
subnet ECS enabled
are allowed to choose how many bits of the address of received
queries to forward, or to reduce the number of bits forwarded for
queries already including an edns-client-subnet ECS option.

5. Option Format

This draft uses an EDNS0 [RFC6891]) option to include client address
information in DNS messages. The option is structured as follows:

+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | FAMILY |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | SOURCE NETMASK PREFIX-LENGTH | SCOPE NETMASK PREFIX-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
7: | ADDRESS... /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

o (Defined in [RFC6891]) OPTION-CODE, 2 octets, for edns-client-
subnet ECS is 8 (0x00
0x08).

o (Defined in [RFC6891]) OPTION-LENGTH, 2 octets, contains the
length of the payload (everything after OPTION-LENGTH) in octets.

o FAMILY, 2 octets, indicates the family of the address contained in
the option, using address family codes as assigned by IANA in
IANA-AFI [2].

The format of the address part depends on the value of FAMILY. This
document only defines the format for FAMILY 1 (IP version 4) and 2
(IP version 6), which are as follows:

o SOURCE NETMASK, PREFIX-LENGTH, an unsigned octet representing the length leftmost
significant bits of the
netmask pertaining ADDRESS to be used for the query. lookup. In replies,
responses, it mirrors the same value as in the requests. It can be set to 0 to disable client-
based lookups, in which case the ADDRESS field MUST be absent. queries.

o SCOPE NETMASK, PREFIX-LENGTH, an unsigned octet representing the length leftmost
significant bits of ADDRESS that the
netmask pertaining to the reply. response covers. In requests, it SHOULD be set to
the longest cacheable length supported by the Intermediate
Nameserver. For backwards compatibiilty with draft versions of
this specification, in requests queries,
it MAY MUST be set to 0 to have the
Authoritative Nameserver treat the longest cacheable length as the
SOURCE NETMASK length. In responses, this field is set by the
Authoritative Nameserver to indicate the coverage of the response.
It might or might not match SOURCE NETMASK; it could be shorter or
longer. 0.

o ADDRESS, variable number of octets, contains either an IPv4 or
IPv6 address, depending on FAMILY, truncated in the request to the number of bits
indicated by the SOURCE NETMASK PREFIX-LENGTH field, with bits set to 0 to
pad up to the end of the last octet used. (This need
not be as many needed. Trailing all-zero octets as a complete address would take.) In the
reply, if the SCOPE NETMASK of the request was 0 then ADDRESS must
contain the same octets as in the request. Otherwise, the bits
for ADDRESS will
SHOULD be significant through the maximum of the SOURCE
NETMASK or SCOPE NETMASK, and 0 filled to the end of an octet. omitted.

All fields are in network byte order ("big-endian", per [RFC1700],
Data Notation).

6. Protocol Description

6.1. Originating the Option

The edns-client-subnet ECS option should generally be added by Recursive Resolvers when
querying other servers, Authoritative Nameservers, as described in Section 11. The
option can also be initialized by a Stub Resolver or Forwarder.

6.1.1. Recursive Resolvers

The setup of the ECS option in a Recursive Resolver depends on the
client query that triggered the resolution process.

In this option, the server should include usual case, where no ECS option was present in the client
query, the Recursive Resolver initializes the option by setting the
FAMILY of the client's address. It then uses the value of its
maximum cacheable prefix length to set SOURCE PREFIX-LENGTH. For
privacy reasons, and because the whole IP address of is rarely required
to determine a tailored response, this length SHOULD be shorter than
the
client that caused full address, as described in Section 10.

If the triggering query to included an ECS option itself, it MUST be generated, truncated
examined for its SOURCE PREFIX-LENGTH. The Recursive Resolver's
outgoing query MUST then set SOURCE PREFIX-LENGTH to the shorter of
the incoming query's SOURCE PREFIX-LENGTH or the server's maximum
cacheable prefix length.

Finally, in both cases, SCOPE PREFIX-LENGTH is set to 0 and the
ADDRESS is then added up to the SOURCE PREFIX-LENGTH number of bits,
with trailing 0 bits specified added, if needed, to fill the final octet. The
total number of octets used should only be enough to cover SOURCE
PREFIX-LENGTH bits, rather than the full width that would normally be
used by addresses in FAMILY.

FAMILY and ADDRESS information MAY be used from the ECS option
incoming query. Passing the existing address data is supportive of
the Recursive Resolver being used as the target of a Forwarder, but
could possibly run into policy problems with regard to usage
agreements between the Recursive Resolver and Authoritative
Namserver. See Section 11.2 for more discussion on this point. If
the Recursive Resolver will not forward the FAMILY and ADDRESS data
from the incoming ECS option, it SHOULD return a REFUSED response.
[*dcl* -- discussion of existing implementations]

Subsequent queries to refresh the data MUST, if unrestricted by an
incoming SOURCE NETMASK field. PREFIX-LENGTH, specify the longest SOURCE PREFIX-
LENGTH that the Recursive Resolver is willing to cache, even if a
previous response indicated that a shorter prefix length was
sufficient.

6.1.2. Stub Resolvers

A Stub Resolver MAY generate DNS queries with an edns-client-subnet ECS option with SOURCE NETMASK set to 0 (i.e. 0.0.0.0/0) to
indicate its own level of privacy via SOURCE PREFIX-LENGTH. An
Intermediate Nameserver that receives such a query MUST NOT make
queries that include more bits of client address than in the
originating query.

A SOURCE PREFIX-LENGTH of 0 means the Recursive Resolver MUST NOT add
address information of the client to its queries. The subsequent
Recursive Resolver query to the Authoritative Nameserver will then
either not include an edns-client-
subnet ECS option or MAY optionally include its own
address information, which is what the Authoritative Nameserver will
almost certainly use anyway to generate the reply any Tailored Response in lieu of no an
option. This allows the answer to be handled by the same caching
mechanism as other requests, queries, with an explicit indicator of the
applicable scope. Subsequent Stub Resolver
requests queries for /0 can then
be answered from this cached response.

The

A Stub Resolver may also add non-empty edns-client-subnet options
to its queries, but Recursive Resolvers are not required MUST set SCOPE PREFIX-LENGTH to use this
information.

For privacy reasons, 0. It MAY include
FAMILY and because the whole IP address is rarely
required to determine an optimized reply, the ADDRESS field in the
option SHOULD data, but should be truncated prepared to handle a certain number of bits, chosen by REFUSED
response if the
administrators Intermediate Nameserver that it queries has a policy
that denies forwarding of the Intermediate Nameserver, ADDRESS. If there is no ADDRESS set,
FAMILY MUST be set to 0.

6.1.3. Forwarders

Forwarders essentially appear to be Stub Resolvers to whatever
Recursive Resolver is ultimately handling the query, but look like a
Recursive Resolver to their client. A Forwarder using this option
MUST prepare it as described in
Section 10.

If the Stub Resolver requests additional privacy via Section 6.1.1 section above. In
particular, a SOURCE NETMASK Forwarder that is shorter than implements this protocol MUST honor
SOURCE PREFIX-LENGTH restrictions indicated in the maximum cacheable SCOPE NETMASK that incoming query
from its client. See also Section 6.5.

Since the Recursive Resolver allows, it contacts will essentially treat it as
a Stub Resolver, the Forwarder must be prepared for a REFUSED
response if the Recursive Resolver SHOULD issue the
query does not permit incoming ADDRESS
information. The Forwarded MUST retry with its longer SCOPE NETMASK. FAMILY and ADDRESS set to
0.

6.2. Generating a Response

6.2.1. Authoritative Nameserver

When a query containing an edns-client-subnet ECS option is received, an Authoritative
Nameserver supporting edns-client-subnet ECS MAY use the address information specified
in the option in order to generate an
optimized reply. a tailored response.

Authoritative Nameservers that have not implemented or enabled
support for the edns-client-subnet ECS option may ought to safely ignore it within incoming queries. Per
queries, per [RFC6891] section 6.1.2, such 6.1.2. Such a server MUST NOT include
an edns-client-subnet ECS option within replies, to indicate lack of support for it.
Implementers of Intermediate Nameservers should be aware, however,
that some nameservers incorrectly echo back unknown EDNS0 options.
In this protocol that should be mostly harmless, as SCOPE PREFIX-
LENGTH should come back as 0, thus marking the option.

Requests response as covering
all networks.

A query with a wrongly formatted options option (e.g., wrong size) an unknown FAMILY)
MUST be rejected and a FORMERR response MUST be returned to the
sender, as described by [RFC6891], Transport Considerations.

If the

An Authoritative Nameserver decides to use information from the
edns-client-subnet that implements this protocol and
receives an ECS option to calculate a response, it MUST include
the an ECS option in the its response to
indicate that it SHOULD be cached accordingly, regardless of whether
the client information was used
and SHOULD needed to formulate an answer. (Note that
the [RFC6891] requirement to reserve space for the OPT record could
mean that the answer section of the response will be cached accordingly. truncated and
fallback to TCP indicated accordingly.) If the an ECS option was not
included in a query, it one MUST NOT be included in the response.

The FAMILY and SOURCE NETMASK in the response MUST match those in even if
the server is providing a Tailored Response -- presumably based on
the
request. address from which it received the query.

The first FAMILY, SOURCE NETMASK bits of the PREFIX-LENGTH and ADDRESS in the response MUST
match those in the request, even if fewer bits were
used to form the response. query. Echoing back the address and netmask these values helps to
mitigate certain attack vectors, as described in Section 10.

The SCOPE NETMASK PREFIX-LENGTH in the reply response indicates the netmask of the network for
which the answer is intended.

A SCOPE NETMASK PREFIX-LENGTH value longer than the SOURCE NETMASK PREFIX-LENGTH
indicates that the address and netmask provided in the query prefix length was not specific enough to
select a single, best response. The ADDRESS MUST be extended to
SCOPE NETMASK significant bits to indicate the network most appropriate Tailored Response. Future queries for which it
is optimal, but
the Recursive Resolver SHOULD still provide the
result as the answer to name within the triggering client request even if specified network SHOULD use the
client is in a different address range. longer SCOPE
PREIX-LENGTH.

Conversely, a shorter SCOPE NETMASK PREFIX-LENGTH indicates that more bits
than necessary were provided, and the answer is suitable for a
broader range of addresses.

If a non-zero SCOPE NETMASK was supplied in This could be as short as 0, to indicate
that the request, answer is suitable for all addresses in FAMILY.

As the SCOPE
NETMASK logical topology of the response MUST be no longer than the SCOPE NETMASK any part of the request.

As not all netblocks are network with regard to the same size,
tailored response can vary, an Authoritative Nameserver may return
different values of SCOPE NETMASK PREFIX-LENGTH for different networks.

In both cases, the value of the SCOPE NETMASK in the reply has strong
implications with regard to how the reply will be cached by
Intermediate Nameservers, as described in Section 6.3.

If the edns-client-subnet option in the request is not used at all, a
server supporting edns-client-subnet MUST indicate that no bits of
the ADDRESS in the request have been used by specifying a SCOPE
NETMASK of 0, equivalent to the networks 0.0.0.0/0 or ::/0. This
could happen, for example, because the reply is invariant across the
network space. The answer is suitable for all clients for the
duration of its TTL.

The specific logic that an Authoritative Nameserver uses to choose an
optimized reply a
tailored response is not in the scope of this document. Implementers
are encouraged, however, to consider carefully their selection of
SCOPE NETMASK PREFIX-LENGTH for the reply response in the event that an optimal reply the best
tailored response cannot be determined.

6.3. Handling edns-client-subnet Replies [Open issue: This seems so
very vague; More text here about possible strategy?]

If the Authoritative Nameserver operator configures a more specific
(longer prefix length) Tailored Response within a configured less
specific (shorter prefix length) Tailored Response, then
implementations can either:

1. Deaggregate the shorter prefix response into multiple longer
prefix responses, or,

2. Alert the operator that the order of queries will determine which
answers get cached, and Caching either warn and continue or treat this as
an error and refuse to load the configuration.

Implementations SHOULD document their chosen behavior.

6.2.2. Intermediate Nameserver

When an Intermediate Nameserver receives uses ECS, whether it passes an ECS
option in its own response to its client is predicated on whether the
client originally included the option. Because a reply containing client that did not
use an edns-
client-subnet ECS option might not be able to understand it, the server MUST
NOT provide one in its response. If the client query did include the
option, the server MUST include one in its response, especially as it will return
could be talking to a Forwarder which would need the information for
its own caching. [Open issue: if the Forwarder sent 0s for FAMILY
and ADDRESS, how could it take back a response with non-zero FAMILY
and ADDRESS when the spec says this mismatch MUST be dropped?]

If an Intermediate Nameserver receives a response which has a longer
SCOPE PREFIX-LENGTH than the SOURCE PREFIX-LENGTH that it 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 different
address range. The Intermediate Nameserver MAY instead opt to retry
with a longer SOURCE PREFIX-LENGTH to get a better reply before
responding to its client, as long as it does not exceed a SOURCE
PREFIX-LENGTH specified in the query that triggered resolution, but
this obviously has implications for the latency of the overall
lookup.

The logic for using the cache to determine whether the Intermediate
Nameserver already knows the response to provide to its client is
covered in the next section.

6.3. Handling ECS Responses and Caching

When an Intermediate Nameserver receives a response containing an ECS
option and without the TC bit set, it SHOULD cache the result. result based
on the data in the option. If the TC bit was set, the Intermediate
Resolver SHOULD retry the query over TCP to get the complete answer
section for caching.

If the FAMILY, SOURCE NETMASK, PREFIX-LENGTH, and SOURCE NETMASK PREFIX-LENGTH bits of
ADDRESS in the reply response don't match the fields in the corresponding request,
query, the full reply response MUST be dropped, as described in Section 10.

If no ECS option is contained in the response, the Intermediate
Nameserver SHOULD treat this as being equivalent to having received a
SCOPE PREFIX-LENGTH of 0, which is an answer suitable for all client
addresses. See further discussion on the security implications of
this in Section 10.

6.3.1. Caching the Response

In the cache, any resource record in the answer section will be tied
to the network specified by the FAMILY, ADDRESS and SCOPE NETMASK PREFIX-
LENGTH fields, as detailed below. limited by the Intermediate Nameserver's own
configuration for maximum cacheable prefix length. Note that the
additional and authority sections from a DNS response message are
specifically excluded here. Any information cached records from these sections MUST NOT
be tied to a network.

If another query is received matching [Open issue: this conflicts a bit with draft-
kumari-dnsop-multiple-responses, which wants to put data in the name and type of
additional section that an entry
in authoritative nameserver that does ECS
would probably want to tailor.] See more at Section 6.4.

Records that are cached as /0 because of a query's SOURCE PREFIX-
LENGTH of 0 MUST be distinguished from those that are cached as /0
because of a response's SCOPE PREFIX-LENGTH of 0. The former should
only be used for other /0 queries that the cache, Intermediate Resolver
receives, but the resolver latter is suitable as a response for all networks.

Although omitting network-specific caching will check whether the FAMILY and ADDRESS
of the client matches one of significantly
simplify an implementation, the networks resulting drop in the cache hits is very
likely to defeat most latency benefits provided by ECS. Therefore,
when implementing this option for that
entry.

If latency purposes, implementing full
caching support as described in this section is strongly recommended.

Enabling support for ECS in an Intermediate Nameserver will
significantly increase the address size of the client is within any cache, reduce the number of
results that can be served from cache, and increase the networks in load on the
cache, then
server. Implementing the cached response MUST be returned mitigation techniques described in
Section 10 is strongly recommended.

6.3.2. Answering from Cache

Cache lookups are first done as usual. If usual for a DNS query, using the
address
query tuple of <name, type, class>. Then the appropriate RRset MUST
be chosen based on longest prefix matching. The client matches multiple networks in address to
use for comparison will depend on whether the cache, Intermediate Nameserver
received an ECS option in its client query.

o If no ECS option was provided, the
entry with client's address is used.

o If there was an ECS option, the longest SCOPE NETMASK value MUST ADDRESS from it MAY be returned, as with
most route-matching algorithms.

If used if
local policy allows. Policy can vary depending on the address agreements
the operator of the client Intermediate Nameserver has with Authoritative
Nameserver operators; see Section 11.2. If policy does not match any allow,
a REFUSED response must be sent.

If a matching network in is found and the cache,
then relevant data is unexpired,
the Recursive Resolver MUST behave response is generated as if per Section 6.2.

If no match was found and matching network is found, the Intermediate Nameserver MUST
perform resolution as usual. This is necessary to avoid suboptimal
replies Tailored
Responses in the cache from being returned to the wrong clients, and
to avoid a single request query coming from a client on a different network
from polluting the cache with a suboptimal reply Tailored Response for all the users
of that resolver.

Note that every time a Recursive Resolver queries an Authoritative
Nameserver by forwarding the edns-client-subnet option that it
received

6.4. Delegations and Negative Answers

The prohibition against tying ECS data to records from another client, a short SOURCE NETMASK the Authority
and Additional section left an unfortunate ambiguity in the original
request could cause a suboptimal reply
specification, primarily with regard to be returned by the
Authoritative Nameserver.

When the request includes a longer SCOPE NETMASK, the reply returned
may still be cached as optimal for the ADDRESS and SCOPE NETMASK negative answers. The
expectation of the reply. This might still be suboptimal for the original client.

To avoid this suboptimal reply from being served from cache for other
clients for which a better reply authors was that ECS would only really be available, the Recursive
Resolver MUST check
used for address records, the SCOPE NETMASK use case that was returned by the
Authoritative Nameserver:

o If driving the SCOPE NETMASK in
definition of the reply protocol.

The delegations case is longer than the SOURCE
NETMASK, it means that the reply might be suboptimal. A Recursive
Resolver MUST return this entry from cache only to queries that do
not contain or allow a longer SOURCE NETMASK bit easier to be forwarded, or tease out. In operational
practice, if an authoritative server is using address information to queries originating from the network covered by
provide customized delegations, it is the ADDRESS and
SCOPE NETMASK..

o If resolver that will be using
the SCOPE NETMASK answer for its next iterative query. Addresses in the reply is shorter than or equal to the
SOURCE NETMASK, the reply is optimal, and Additional
section SHOULD be returned from
cache to any client within the network indicated by ADDRESS therefore ignore ECS data, and
SCOPE NETMASK.

As another reply is received, the reply will be tied to a different
network. The server authority SHOULD keep in cache both replies, and
return
the most appropriate one depending a zero SCOPE PREFIX-LENGTH on the address of the client. Per
standard DNS caching behavior, all records delegations. A recursive
resolver SHOULD be retained until
their TTL expires. Subsequent queries to refresh the data should
always specify the longest SCOPE NETMASK that the Recursive Resolver
is willing to cache, even if previous responses indicated that treat a
shorter netmask was the optimal response.

Although omitting network-specific caching will significantly
simplify an implementation, the resulting drop non-zero SCOPE PREFIX LENGTH in cache hits is very
likely to defeat most latency benefits provided by edns-client-
subnet. Therefore, when implementing this option for latency
purposes, implementing full caching support a delegation
as described in this though it were zero.

For negative answers, some independent implementations of both
resolvers and authorities did not see the section is STRONGLY RECOMMENDED.

Any reply containing an edns-client-subnet option considered invalid
should be treated restriction as if no edns-client-subnet option was specified at
all.

Replies coming from servers not supporting edns-client-subnet
necessarily meaning that a given name and type must only have either
positive ECS-tagged answers or
otherwise not containing an edns-client-subnet option SHOULD be
considered as containing a SCOPE NETMASK negative answer. They support being
able to tell one part of 0 (e.g., cache the result
for 0.0.0.0/0 or ::/0) for all the supported families.

In any case, network that the response from data does not exist,
while telling another part of the resolver network that it does.

Several other implementations, however, do not support being able to the client MUST NOT
contain the edns-client-subnet option if none was present in the
client's original request. If the original client request contained
mix positive and negative answers, and thus interoperability is a valid edns-client-subnet option that was used during recursion, the
Recursive Resolver MUST include the edns-client-subnet option from
the Authoritative Nameserver response in the response
problem.

This issue is expected to the client.

Enabling support for edns-client-subnet be revisited in a recursive resolver will
significantly increase the size future revision of the cache, reduce
protocol, possibly blessing the number mixing of
results that can be served from cache, positive and increase the load on the
server. Implementing the mitigation techniques described in
Section 10 is strongly recommended.

6.4. negative
answers. There are implications for cache data structures that
developers should consider when writing new ECS code.

6.5. Transitivity

Generally, edns-client-subnet ECS options will only be present in DNS messages between a
Recursive Resolver and an Authoritative Nameserver, i.e., one hop.
In certain configurations however, for example multi-tier nameserver
setups, it may be necessary to implement transitive behaviour on
Intermediate Nameservers.

It is important that any Intermediate Nameserver that forwards edns-
client-subnet ECS
options received from their clients MUST fully implement the caching
behaviour described in Section 6.3.

Intermediate Nameservers, including Recursive Resolvers, Nameservers supporting
edns-client-subnet ECS MUST forward options with
SOURCE NETMASK PREFIX-LENGTH set to 0
(i.e., (that is, completely anonymized), such an option MUST
forward the query with SOURCE PREFIX-LENGTH set to 0 and MUST NOT be
replaced with an option with more accurate address information.

An Intermediate Nameserver MAY also forward edns-client-subnet ECS options with actual
address information. This information MAY match the source IP
address of the incoming query, and MAY have more or
less fewer address
bits than the Nameserver would normally include in a locally
originated edns-client-subnet ECS option.

If for any reason the Intermediate Nameserver does not want to use
the information in an edns-client-subnet ECS option it receives (too little address
information, network address from a range not authorized to use the
server, private/unroutable address space, etc), it SHOULD drop the
query and return a REFUSED response. Note again that an edns-client-subnet ECS option
with 0 address bits MUST NOT be refused.

Be aware that at least one major existing implementation does not
return REFUSED and instead just process the query as though the
problematic information were not present. This can lead to anomalous
situations, such as a response from the Intermediate Nameserver that
indicates it is tailored for one network (the one passed in the
original query, since ADDRESS must match) when actually it is for
another network (the one which contains the address that the
Intermediate Nameserver saw as making the query).

7. IANA Considerations

IANA has already assigned option code 8 in the "DNS EDNS0 Option
Codes (OPT)" registry to edns-client-subnet. ECS.

The IANA is requested to update the reference ("draft-vandergaast-
edns-client-subnet") to refer to this RFC when published.

8. DNSSEC Considerations

The presence or absence of an [RFC6891] EDNS0 OPT resource record
containing an edns-client-subnet ECS option in a DNS query does not change the usage of
the resource records and mechanisms used to provide data origin
authentication and data integrity to the DNS, as described in
[RFC4033], [RFC4034] and [RFC4035]. OPT records are not signed.

Use of this option, however, does imply increased DNS traffic between
any given Recursive Resolver and Authoritative Nameserver, which
could be another barrier to further DNSSEC adoption in this area.

9. NAT Considerations

Special awareness of edns-client-subnet ECS in devices that perform Network Address
Translation (NAT) as described in [RFC2663] is not required; queries
can be passed through as-is. The client's network address SHOULD NOT
be added, and existing edns-client-subnet ECS options, if present, SHOULD NOT be
modified by NAT devices.

In large-scale global networks behind a NAT (but, device (but for example, example
with a Centralized Resolver infrastructure), an internal Intermediate
Nameserver might have detailed network layout information, and might may
know which external subnets are used for egress traffic by each
internal network. In such cases, the Intermediate Nameserver MAY use
that information when originating edns-client-subnet ECS options.

In other cases, Recursive Resolvers sited behind a NAT device SHOULD
NOT originate edns-client-subnet ECS options with their external IP address, and instead
rely on downstream Intermediate Nameservers doing so. They MAY,
however, choose to include the option with their internal address for
the purposes of signaling a shorter, more anonymous SOURCE NETMASK. PREFIX-
LENGTH.

If an Authoritative Nameserver on the publicly routed Internet
receives a request query that specifies an ADDRESS in [RFC1918] or [RFC4193]
private address space, it SHOULD ignore ADDRESS and look up its
answer based on the address of the Recursive Resolver. In the
reply
response it SHOULD set SCOPE NETMASK PREFIX-LENGTH to cover all of the
relevant private space. For example, a request query for ADDRESS 10.1.2.0
with a SOURCE NETMASK PREFIX-LENGTH of 24 would get a returned SCOPE NETMASK PREFIX-
LENGTH of 8. The Intermediate Nameserver MAY elect to cache the
answer under one entry for special-purpose addresses [RFC6890]; see
Section 10.3.

10. Security Considerations

10.1. Privacy

With the edns-client-subnet ECS option, the network address of the client that initiated
the resolution becomes visible to all servers involved in the
resolution process. Additionally, it will be visible from any
network traversed by the DNS packets.

To protect users' privacy, Recursive Resolvers are strongly
encouraged to conceal part of the IP address of the user by
truncating IPv4 addresses to 24 bits. No recommendation is provided
for IPv6 at this time, but IPv6 addresses should be similarly
truncated in order to not allow unique identification of the client.

When a non-zero SCOPE NETMASK is provided by the Recursive Resolver
that is longer than SOURCE NETMASK, users can often obtain more
optimal mapping if the resolver is well-used. Replies will have
answers optimized up to SCOPE NETMASK 56 bits are recommended for a subset of the SOURCE
NETMASK. Subsequent requests within the TTL from clients within the
cached range will be served the optimal answer, while still
preserving privacy of the user.
IPv6, based on [RFC6177].

ISPs will often should have more detailed knowledge of their own networks. That
is, they will might know if that all 24-bit prefixes in a /20 are in the same
area. In those cases, for optimal cache utilization and improved
privacy, the ISP's Recursive Resolver SHOULD truncate IP addresses in
this /20 to just 20 bits, instead of 24 as recommended above.

Users who wish their full IP address to be hidden can include an
edns-client-subnet ECS
option specifying the wildcard address 0.0.0.0/0 (i.e. FAMILY set to 1 (IPv4), SOURCE NETMASK to 0 and no ADDRESS). PREFIX-LENGTH of
0). As described in previous sections, this option will be forwarded
across all the Recursive Resolvers supporting edns-client-subnet, ECS, which MUST NOT
modify it to include the network address of the client.

Note that even without an edns-client-subnet ECS option, any server queried directly by
the user will be able to see the full client IP address. Recursive
Resolvers or Authoritative Nameservers MAY use the source IP address
of requests queries to return a cached entry or to generate an optimized reply a Tailored
Response that best matches the request. query.

10.2. Birthday Attacks

edns-client-subnet

ECS adds information to the DNS question tuple query tupe (q-tuple). This allows an
attacker to send a caching Intermediate Nameserver multiple queries
with spoofed IP addresses either in the
edns-client-subnet ECS option or as the source
IP. These queries will trigger multiple outgoing queries with the
same name, type and class, just different address information in the edns-client-subnet
ECS option.

With multiple queries for the same name in flight, the attacker has a
higher chance of success in sending to send a matching response (with with the
address 0.0.0.0/0 SCOPE
PREFIX-LENGTH set to 0 to get it cached for many hosts). all hosts.

To counter this, every edns-client-subnet ECS option in a response packet MUST contain
the FAMILY full FAMILY, ADDRESS and SOURCE NETMASK PREFIX-LENGTH fields from the
corresponding request, along with identical ADDRESS bits for SOURCE
NETMASK length. query. Intermediate Nameservers processing a response
MUST verify that these match, and MUST SHOULD discard the entire reply response
if they do not.

That requirement to discard is "SHOULD" instead of "MUST" because it
stands in opposition to the instruction in Section 6.3 which states
that a response lacking an ECS option should be treated as though it
had one of SCOPE PREFIX-LENGTH of 0. If that is always true, then an
attacker does not need to worry about matching the original ECS
option data and just needs to flood back responses that have no ECS
option at all.

This type of attack could be detected in ongoing operations by
marking whether the responding nameserver had previously been sending
ECS option, and/or by taking note of an incoming flood of bogus
responses and flagging the relevant query for re-resolution. This is
more complex than existing nameserver responses to spoof floods, and
would also need to be sensitive to a nameserver legitimately stopping
ECS replies even though it had previously given them.

10.3. Cache Pollution

It is simple for an arbitrary resolver or client to provide false
information in the edns-client-subnet ECS option, or to send UDP packets with forged
source IP addresses.

This could be used to:

o pollute the cache of intermediate resolvers, by filling it with
results that will rarely (if ever) be used.

o reverse engineer the algorithms (or data) used by the
Authoritative Nameserver to calculate the optimized answer. Tailored Responses.

o mount a denial-of-service attack against an Intermediate
Nameserver, by forcing it to perform many more recursive queries
than it would normally do, due to how caching is handled for
queries containing the edns-client-subnet ECS option.

Even without malicious intent, Centralized Resolvers providing
answers to clients in multiple networks will need to cache different
replies
responses for different networks, putting more memory pressure on the
cache.

To mitigate those problems:

o Recursive Resolvers implementing edns-client-subnet ECS should only enable it in
deployments where it is expected to bring clear advantages to the
end users. For example, when expecting clients from a variety of
networks or from a wide geographical area. Due to the high cache
pressure introduced by edns-client-subnet, ECS, the feature SHOULD be disabled in all
default configurations.

o Recursive Resolvers SHOULD limit the number of networks and
answers they keep in the cache for a given query.

o Recursive Resolvers SHOULD limit the number of total different
networks that they keep in cache.

o Recursive Resolvers should MUST never send edns-client-subnet options an ECS option with a SCOPE NETMASK that is longer than they are willing to
cache. Similarly, if using the backwards-compatible SCOPE NETMASK
of 0, the request should not set a SOURCE NETMASK of
PREFIX-LENGTH providing more bits in the ADDRESS than they are
willing to cache. cache responses for.

o Recursive Resolvers should implement algorithms to improve the
cache hit rate, given the size constraints indicated above.
Recursive Resolvers MAY, for example, decide to discard more
specific cache entries first.

o Authoritative Nameservers and Recursive Resolvers should discard
edns-client-subnet
ECS options that are either obviously forged or otherwise known to
be wrong. They SHOULD at least treat unroutable addresses, such
as some of the address blocks defined in [RFC6890], as equivalent
to the Recursive Resolver's own identity. They SHOULD ignore and
never forward edns-client-subnet ECS options specifying other routable addresses that
are known not to be served by the query source.

o Authoritative Nameservers consider the edns-client-subnet ECS option just as a hint
to provide better results. They can decide to ignore the content
of the edns-client-subnet ECS option based on black or white lists, rate limiting
mechanisms, or any other logic implemented in the software.

11. Sending the Option

When implementing a Recursive Resolver, there are two strategies on
deciding when to include an edns-client-subnet ECS option in a query. At this stage,
it's not clear which strategy is best.

11.1. Probing

A Recursive Resolver can send the edns-client-subnet ECS option with every outgoing
query. However, it is RECOMMENDED that Resolvers remember which
Authoritative Nameservers did not return the option with their
response, and omit client address information from subsequent queries
to those Nameservers.

Additionally, Recursive Resolvers MAY SHOULD be configured to never send
the option when querying root, top-level, and effective top-level
domain servers. These domains are delegation-centric and are very
unlikely to generate different replies responses based on the address of the
client.

When probing, it is important that several things are probed: support
for edns-client-subnet, ECS, support for EDNS0, support for EDNS0 options, or possibly an
unreachable Nameserver. Various implementations are known to drop
DNS packets with OPT RRs (with or without options), thus several
probes are required to discover what is supported.

Probing, if implemented, MUST be repeated periodically (i.e. daily). periodically, e.g., daily.
If an Authoritative Nameserver indicates edns-client-subnet ECS support for one zone, it
is to be expected that the Nameserver supports edns-
client-subnet ECS for all of its
zones. Likewise, an Authoritative Nameserver that uses edns-client-subnet ECS
information for one of its zones, MUST indicate support for the
option in all of its responses. responses to ECS queries. If the option is
supported but not actually used for generating a response, its SCOPE NETMASK value
PREFIX-LENGTH SHOULD be set to 0.

11.2. Whitelist

As described previously, it is expected that only a few Recursive
Resolvers will need to use edns-client-subnet, ECS, and that it will generally be enabled
only if it offers a clear benefit to the users.

To avoid the complexity of implementing a probing and detection
mechanism (and the possible query loss/delay that may come with it),
an implementation could decide to use a statically configured whitelist of Authoritative Namesevers
to send the option to. to, likely specified by their domain name.
Implementations MAY also allow additionally configuring this based on
other criteria, such as zone or query type.

An additional advantage of using a whitelist is that partial client
address information is only disclosed to Nameservers that are known
to use the information, improving privacy.

A major drawback is scalability. The operator needs to track which
Authoritative Nameservers support edns-client-subnet, ECS, making it harder for new
Authoritative Nameservers to start using the option.

Similarly, Authoritative Nameservers can also use whitelists to limit
the feature to only certain clients. For example, a CDN that does
not want all of their mapping trivially walked might require a legal
agreement with the Recursive Resolver operator, to clearly describe
the acceptable use of the feature.

The maintenance of access control mechanisms is out of scope for this
protocol definition.

12. Example

1. A stub resolver SR resolver, SR, with IP address 192.0.2.37 tries to resolve
www.example.com, by forwarding the query to the Recursive
Resolver R
Resolver, RNS, from IP address IP, asking for recursion.

2. RNS, supporting edns-client-subnet, ECS, looks up www.example.com in its cache. An
entry is found neither for www.example.com, nor for example.com.

3. RNS builds a query to send to the root and .com servers. The
implementation of R RNS provides facilities so an administrator
can configure RNS it not to forward edns-client-subnet ECS in certain cases. In
particular, RNS is configured to not include an edns-
client-subnet ECS option when
talking to delegation-centric TLD or root nameservers, as described in Section 6.1.
Thus, no edns-client-
subnet ECS option is added, and resolution is performed as
usual.

4. RNS now knows the next server to query, query: the Authoritative Nameserver
Nameserver, ANS, responsible for example.com.

5. RNS prepares a new query for www.example.com, including an edns-
client-subnet ECS
option with:

* OPTION-CODE, set to 0x00 0x08. 8.

* OPTION-LENGTH, set to 0x00 0x07 for the following fixed 4
octets plus the 3 octets that will be used for ADDRESS.

* FAMILY, set to 0x00 0x01 as IP is an IPv4 address.

* SOURCE NETMASK, PREFIX-LENGTH, set to 0x18, as RNS is configured to
conceal the last 8 bits of every IPv4 address.

* SCOPE NETMASK, PREFIX-LENGTH, set to 0x1B, 0x00, as RNS is willing to cache
answers up to a /27. specified by this
document for all queries.

* ADDRESS, set to 0xC0 0x00 0x02, providing only the first 24
bits of the IPv4 address.

6. The query is sent. Server ANS understands and uses edns-client-
subnet. ECS. It parses the edns-client-subnet
ECS option, and generates
an optimized reply. a Tailored Response.

7. Due to the its internal implementation of ANS, it implementation, ANS finds an answer a response that is optimal
tailored for several /27 ranges within the ADDRESS/SOURCE
NETMASK whole /16 of the request. It chooses one randomly. (Note well,
this is just one example of how ANS could pick a suitable
answer. Other selection methods are possible.) client that performed the
query.

8. The Authoritative Nameserver ANS adds an edns-client-subnet ECS option in the reply, response, containing:

* OPTION-CODE, set to 0x00 0x08. 8.

* OPTION-LENGTH, set to 0x00 0x08 for the following fixed 4
octets plus the 4 octets that will be used for ADDRESS . 0x07.

* FAMILY, set to 0x00 0x01, the same as the request. 0x01.

* SOURCE NETMASK, PREFIX-LENGTH, set to 0x18, copied from the request. query.

* SCOPE NETMASK, PREFIX-LENGTH, set to 0x1B, 0x10, indicating a /27 /16 network.

* ADDRESS, set to 0xC0 0x00 0x02 0xE0, 0x02, copied from the request. query.

9. RNS receives the reply response containing an edns-client-subnet ECS option.
The resolver It verifies
that FAMILY, SOURCE NETMASK, PREFIX-LENGTH, and the
SOURCE NETMASK bits of ADDRESS match the request. query.
If not, the message is discarded.

10. The reply response is interpreted as usual. Since the reply response
contains an
edns-client-subnet ECS option, the ADDRESS, SCOPE NETMASK, PREFIX-LENGTH, and
FAMILY in the response are used to cache the entry.

11. RNS sends a response to stub resolver SR, without including an
edns-client-subnet
ECS option.

12. RNS receives another request query to resolve www.example.com. This
time, a reply response is cached. The reply, response, however, is tied to a
particular network. If the address of the client matches any
network in the cache, then the reply response is returned from the
cache. Otherwise, another query is performed. If multiple
results match, the one with the longest SCOPE NETMASK PREFIX-LENGTH is
chosen, as per common best-network match algorithms.

13. Contributing Authors

The below individuals contributed significantly to the draft. The
RFC Editor prefers a maximum of 5 names on the front page, and so we
have listed additional authors in this section

Edward Lewis
ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, Angeles CA 90094-2536
USA
Email: edward.lewis@icann.org

Sean Leach
Fastly
POBox 78266
San Francisco, Francisco CA 94107

Jason Moreau
Akamai Technologies
8 Cambridge Ctr
Cambridge MA 02142-1413
USA

14. Acknowledgements

The authors wish to thank Darryl Rodden for his work as a co-author
on previous versions, and the following people for reviewing early
drafts of this document and for providing useful feedback: Paul S.

R. Chisholm, B. Narendran, Leonidas Kontothanassis, David Presotto,
Philip Rowlands, Chris Morrow, Kara Moscoe, Alex Nizhner, Warren
Kumari, and Richard Rabbat from Google, Google; Terry Farmer, Mark Teodoro,
Edward Lewis, and Eric Burger from Neustar, Neustar; David Ulevitch, Ulevitch and
Matthew Dempsky from OpenDNS, OpenDNS; Patrick W. Gilmore and Jason Moreau Steve Hill from
Akamai,
Akamai; Colm MacCarthaigh, MacCarthaigh and Richard Sheehan from Amazon; Tatuya
Jinmei from Internet Software Consortium; Andrew Sullivan from Dyn;
John Dickinson from Sinodun; Mark Delany from Apple; Yuri Schaeffer
from NLnet Labs; Antonio Querubin; and all of the other people that
replied to our emails on various mailing lists.

15. References

15.1. 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.

[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.

[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.

[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.

[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.

[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.

[RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address
Assignment to End Sites", BCP 157, RFC 6177, March 2011.

[RFC6890] Cotton, M., Vegoda, L., Bonica, R., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153, RFC
6890, April 2013.

[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.

15.2. Informative References

[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.

15.3. URIs

[1] http://www.iana.org/assignments/address-family-numbers/

Appendix A. Document History

[RFC Editor: Please delete this section before publication.]

-00 to -01 (IETF)

o <David> Made the document describe how things are actually
implmented now. This makes the document be more of a "this is how
we are doing things, this provides information on that". There
may be a future document that describes additional funcationality.

o NETMASK was not a good desription, changed to PREFIX-LENGTH
(Jinmei, others). Stole most of the definition for prefix length
from RFC4291.

o Fixed the "SOURCE PREFIX-LENGTH set to 0" definition to include
IPv6 (Tatuya Jinmei)

o Comment that ECS cannot be used to hand NXDOMAIN to some clients
and not others, primarily because of interoperability issues.
(Tatuya Jinmei)

o Added text explaining that implmentations need to document thier
behavior with overlapping networks.

o Soften "optimized reply" language. (Andrew Sullivan).

o Fixed some of legacy IPv4 cruft (things like 0.0.0.0/0)

o Some more grammar / working cleanups.

o Replaced a whole heap of occurances of "edns-client-subnet" with
"ECS" for readability. (John Dickinson)

o More clearly describe the process from the point of view of each
type of nameserver. (John Dickinson)

o Birthday attack still possible if attacker floods with ECS-less
responses. (Yuri Schaeffer)

o Added some open issues directly to the text.

A.1. -00

o Document moved to experimental track, added experiment description
in header with details in a new section.

o Specifically note that edns-client-subnet ECS applies to the answer section only.

o Warn that caching based on edns-client-subnet ECS is optional but very important for
performance reasons.

o Updated NAT section.

o Added recommendation to not use the default /24 recommendation for
the source netmask prefix-length field if more detailed information about
the network is available.

o Rewritten problem statement to be more clear about the goal of
edns-client-subnet ECS
and the fact that it's entirely optional.

o Wire format changed to include the original address and netmask prefix
length in responses in defence against birthday attacks.

o Security considerations now includes a section about birthday
attacks.

o Renamed edns-client-ip in edns-client-subnet, ECS, following suggestions on the
mailing list.

o Clarified behavior of resolvers when presented with an invalid
edns-client-subnet ECS
option.

o Fully take multi-tier DNS setups in mind and be more clear about
where the option should be originated.

o A note on Authoritative Nameservers receiving queries that specify
private address space.

o A note to always ask for the longest acceptable SOURCE prefix
length, even if a prior answer indicated that a shorter prefix
length was suitable.

o Marked up a few more references.

o Added a few definitions in the Terminology section, and a few more
aesthetic changes in the rest of the document.

A.2. -01

o Document version number reset from -02 to -00 due to the rename to
edns-client-subnet.
ECS.

o Clarified example (dealing with TLDs, and various minor errors).

o Referencing RFC5035 instead of RFC1918.

o Added a section on probing (and how it should be done) vs.
whitelisting.

o Moved description on how to forward edns-client-subnet ECS option in dedicated
section.

o Queries with wrongly formatted edns-client-subnet ECS options should now be rejected
with FORMERR.

o Added an "Overview" section, providing an introduction to the
document.

o Intermediate Nameservers can now remove an edns-client-subnet ECS option, or reduce
the SOURCE NETMASK PREFIX-LENGTH to increase privacy.

o Added a reference to DoS attacks in the Security section.

o Don't use "network range", as it seems to have different meaning
in other contexts, and turned out to be confusing.

o Use shorter and longer netmasks, prefix lengths, rather than higher or
lower. Add a better explanation in the format section.

o Minor corrections in various other sections.

A.3. -02

o Added IANA-assigned option code.

A.4. -03*

o [*] There was no -03 version of the draft; these changes, however,
were made after -02.

o Allow non-zero SCOPE NETMASK for Recursive Resolvers to indicate
their maximum cacheable mask length, and updated the example
accordingly.

o A note on Authoritative Nameservers receiving requests that
specify private address space.

o A note to always ask for the longest acceptable SCOPE NETMASK,
even if a prior answer indicated that a shorter netmask was
optimal.

o Marked up a couple of references.

o Minor grammatical consistency edits.

Authors' Addresses

Carlo Contavalli
Google
1600 Amphitheater Parkway
Mountain View, CA 94043
US

Email: ccontavalli@google.com

Wilmer van der Gaast
Google
Belgrave House, 76 Buckingham Palace Road
London SW1W 9TQ
UK

Email: wilmer@google.com

David C Lawrence
Akamai Technologies
8 Cambridge Center
Cambridge, MA 02142
US

Email: tale@akamai.com

Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US

Email: warren@kumari.net