draft-ietf-dnsop-no-response-issue-04.txt   draft-ietf-dnsop-no-response-issue-05.txt 
Network Working Group M. Andrews Network Working Group M. Andrews
Internet-Draft ISC Internet-Draft ISC
Intended status: Best Current Practice August 26, 2016 Intended status: Best Current Practice September 18, 2016
Expires: February 27, 2017 Expires: March 22, 2017
A Common Operational Problem in DNS Servers - Failure To Respond. A Common Operational Problem in DNS Servers - Failure To Respond.
draft-ietf-dnsop-no-response-issue-04 draft-ietf-dnsop-no-response-issue-05
Abstract Abstract
The DNS is a query / response protocol. Failure to respond or to The DNS is a query / response protocol. Failure to respond or to
respond correctly to queries causes both immediate operational respond correctly to queries causes both immediate operational
problems and long term problems with protocol development. problems and long term problems with protocol development.
This document identifies a number of common kinds of queries to which This document identifies a number of common kinds of queries which
some servers either fail to respond or else respond incorrectly. some servers either fail to respond or else respond incorrectly.
This document also suggests procedures for TLD and other similar zone This document also suggests procedures for TLD and other zone
operators to apply to help reduce / eliminate the problem. operators to apply to help reduce / eliminate the problem.
The document does not look at the DNS data itself, just the structure The document does not look at the DNS data itself, just the structure
of the responses. of the responses.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 27, 2017. This Internet-Draft will expire on March 22, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Common queries kinds that result in non responses. . . . . . 4 2. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Basic DNS Queries . . . . . . . . . . . . . . . . . . . . 4 3. Common queries kinds that result in non responses. . . . . . 4
2.1.1. Unknown / Unsupported Type Queries . . . . . . . . . 4 3.1. Basic DNS Queries . . . . . . . . . . . . . . . . . . . . 5
2.1.2. DNS Flags . . . . . . . . . . . . . . . . . . . . . . 4 3.1.1. Zone Existence . . . . . . . . . . . . . . . . . . . 5
2.1.3. Unknown DNS opcodes . . . . . . . . . . . . . . . . . 4 3.1.2. Unknown / Unsupported Type Queries . . . . . . . . . 5
2.1.4. TCP Queries . . . . . . . . . . . . . . . . . . . . . 5 3.1.3. DNS Flags . . . . . . . . . . . . . . . . . . . . . . 5
2.2. EDNS Queries . . . . . . . . . . . . . . . . . . . . . . 5 3.1.4. Unknown DNS opcodes . . . . . . . . . . . . . . . . . 5
2.2.1. EDNS Queries - Version Independent . . . . . . . . . 5 3.1.5. TCP Queries . . . . . . . . . . . . . . . . . . . . . 6
2.2.2. EDNS Queries - Version Specific . . . . . . . . . . . 5 3.2. EDNS Queries . . . . . . . . . . . . . . . . . . . . . . 6
2.2.3. EDNS Options . . . . . . . . . . . . . . . . . . . . 6 3.2.1. EDNS Queries - Version Independent . . . . . . . . . 6
2.2.4. EDNS Flags . . . . . . . . . . . . . . . . . . . . . 6 3.2.2. EDNS Queries - Version Specific . . . . . . . . . . . 6
3. Remediating . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.3. EDNS Options . . . . . . . . . . . . . . . . . . . . 7
4. Firewalls and Load Balancers . . . . . . . . . . . . . . . . 8 3.2.4. EDNS Flags . . . . . . . . . . . . . . . . . . . . . 7
5. Scrubbing Services . . . . . . . . . . . . . . . . . . . . . 9 3.2.5. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 7
6. Whole Answer Caches . . . . . . . . . . . . . . . . . . . . . 10 4. Remediating . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Response Code Selection . . . . . . . . . . . . . . . . . . . 10 5. Firewalls and Load Balancers . . . . . . . . . . . . . . . . 9
8. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Scrubbing Services . . . . . . . . . . . . . . . . . . . . . 10
8.1. Testing - Basic DNS . . . . . . . . . . . . . . . . . . . 11 7. Whole Answer Caches . . . . . . . . . . . . . . . . . . . . . 10
8.1.1. Is The Server Configured For The Zone? . . . . . . . 11 8. Response Code Selection . . . . . . . . . . . . . . . . . . . 11
8.1.2. Testing Unknown Types? . . . . . . . . . . . . . . . 12 9. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1.3. Testing Header Bits . . . . . . . . . . . . . . . . . 12 9.1. Testing - Basic DNS . . . . . . . . . . . . . . . . . . . 12
8.1.4. Testing Unknown Opcodes . . . . . . . . . . . . . . . 13 9.1.1. Is The Server Configured For The Zone? . . . . . . . 12
8.1.5. Testing TCP . . . . . . . . . . . . . . . . . . . . . 13 9.1.2. Testing Unknown Types? . . . . . . . . . . . . . . . 12
8.2. Testing - Extended DNS . . . . . . . . . . . . . . . . . 13 9.1.3. Testing Header Bits . . . . . . . . . . . . . . . . . 13
8.2.1. Testing Minimal EDNS . . . . . . . . . . . . . . . . 14 9.1.4. Testing Unknown Opcodes . . . . . . . . . . . . . . . 14
8.2.2. Testing EDNS Version Negotiation . . . . . . . . . . 14 9.1.5. Testing TCP . . . . . . . . . . . . . . . . . . . . . 14
8.2.3. Testing Unknown EDNS Options . . . . . . . . . . . . 14 9.2. Testing - Extended DNS . . . . . . . . . . . . . . . . . 14
8.2.4. Testing Unknown EDNS Flags . . . . . . . . . . . . . 15 9.2.1. Testing Minimal EDNS . . . . . . . . . . . . . . . . 15
8.2.5. Testing EDNS Version Negotiation With Unknown EDNS 9.2.2. Testing EDNS Version Negotiation . . . . . . . . . . 15
Flags . . . . . . . . . . . . . . . . . . . . . . . . 15 9.2.3. Testing Unknown EDNS Options . . . . . . . . . . . . 15
8.2.6. Testing EDNS Version Negotiation With Unknown EDNS 9.2.4. Testing Unknown EDNS Flags . . . . . . . . . . . . . 16
9.2.5. Testing EDNS Version Negotiation With Unknown EDNS
Flags . . . . . . . . . . . . . . . . . . . . . . . . 16
9.2.6. Testing EDNS Version Negotiation With Unknown EDNS
Options . . . . . . . . . . . . . . . . . . . . . . . 16 Options . . . . . . . . . . . . . . . . . . . . . . . 16
8.2.7. Testing DNSSEC Queries . . . . . . . . . . . . . . . 16 9.2.7. Testing DNSSEC Queries . . . . . . . . . . . . . . . 17
8.2.8. Testing EDNS Version Negotiation With DNSSEC . . . . 16 9.2.8. Testing EDNS Version Negotiation With DNSSEC . . . . 17
8.2.9. Testing With Multiple Defined EDNS Options . . . . . 17 9.2.9. Testing With Multiple Defined EDNS Options . . . . . 18
8.2.10. When EDNS Is Not Supported . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 9.3. When EDNS Is Not Supported . . . . . . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 19 12.1. Normative References . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 12.2. Informative References . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
The DNS [RFC1034], [RFC1035] is a query / response protocol. Failure The DNS [RFC1034], [RFC1035] is a query / response protocol. Failure
to respond to queries or to respond incorrectly causes both immediate to respond to queries or to respond incorrectly causes both immediate
operational problems and long term problems with protocol operational problems and long term problems with protocol
development. development.
Failure to respond to a query is indistinguishable from a packet loss Failure to respond to a query is indistinguishable from a packet
without doing a analysis of query response patterns and results in loss. Without doing a analysis of query response patterns will
unnecessary additional queries being made by DNS clients and results in unnecessary additional queries being made by DNS clients,
unnecessary delays being introduced to the resolution process. and delays being introduced to the resolution process.
Due to the inability to distinguish between packet loss and Due to the inability to distinguish between packet loss and
nameservers dropping EDNS [RFC6891] queries, packet loss is sometimes nameservers dropping EDNS [RFC6891] queries, packet loss is sometimes
misclassified as lack of EDNS support which can lead to DNSSEC misclassified as lack of EDNS support which can lead to DNSSEC
validation failures. validation failures.
Allowing servers which fail to respond to queries to remain results Servers which fail to respond to queries to remain results in
in developers being afraid to deploy implementations of recent developers being hesitant to deploy new standards. Such servers need
standards. Such servers need to be identified and corrected / to be identified.
replaced.
The DNS has response codes that cover almost any conceivable query The DNS has response codes that cover almost any conceivable query
response. A nameserver should be able to respond to any conceivable response. A nameserver should be able to respond to any conceivable
query using them. query using them.
Unless a nameserver is under attack, it should respond to all queries Unless a nameserver is under attack, it should respond to all queries
directed to it as a result of following delegations. Additionally directed to it. Additionally, the nameserver should not assume that
code should not assume that there isn't a delegation to the server there isn't a delegation to the server even if it is not configured
even if it is not configured to serve the zone. Broken delegations to serve the zone. Broken nameservers are a common occurrence in the
are a common occurrence in the DNS and receiving queries for zones DNS and receiving queries for zones that the server is not configured
that the server is not configured for is not necessarily an for is not necessarily an indication that the server is under attack.
indication that the server is under attack. Parent zone operators Parent zone operators are supposed to regularly check that the
are supposed to regularly check that the delegating NS records are delegating NS records are consistent with those of the delegated zone
consistent with those of the delegated zone and to correct them when and to correct them when they are not [RFC1034]. Doing this
they are not [RFC1034]. If this was being done regularly, the regularly should reduce the instances of broken delegations.
instances of broken delegations would be much lower.
When a nameserver is under attack it may wish to drop packets. A When a nameserver is under attack it may wish to drop packets. A
common attack is to use a nameserver as a amplifier by sending common attack is to use a nameserver as a amplifier by sending
spoofed packets. This is done because response packets are bigger spoofed packets. This is done because response packets are bigger
than the queries and big amplification factors are available than the queries and big amplification factors are available
especially if EDNS is supported. Limiting the rate of responses is especially if EDNS is supported. Limiting the rate of responses is
reasonable when this is occurring and the client should retry. This reasonable when this is occurring and the client should retry. This
however only works if legitimate clients are not being forced to however only works if legitimate clients are not being forced to
guess whether EDNS queries are accepted or not. While there is still guess whether EDNS queries are accepted or not. While there is still
a pool of servers that don't respond to EDNS requests, clients have a pool of servers that don't respond to EDNS requests, clients have
no way to know if the lack of response is due to packet loss, EDNS no way to know if the lack of response is due to packet loss, EDNS
packets not being supported or rate limiting due to the server being packets not being supported or rate limiting due to the server being
under attack. Mis-classifications of server characteristics are under attack. Mis-classifications of server characteristics are
unavoidable when rate limiting is done. unavoidable when rate limiting is done.
2. Common queries kinds that result in non responses. 2. Consequences
There are number common query kinds that result in non responses Lack of following the relevant RFCs has lead to various consequences.
today. These are EDNS queries with and without extensions, queries Some as a direct result and some from recursive servers try to work
for unknown (unallocated) or unsupported types, and filtering of TCP around the non compliance. Fixing known issues know will reduce
future consequences as DNS clients make use of the features available
in the DNS protocol.
The AD flag bit in a response cannot be trusted to mean anything as
servers incorrectly copied the flag bit from the request to the
response despite the prohibition.
Wide spread non response to EDNS queries has lead to recursive
servers having to assume EDNS may not supported and fallback to plain
DNS is required. Servers get incorrectly diagnosed as not supporting
EDNS and when they also serve signed zones DNSSEC validation fails.
Similarly, wide spread non response to EDNS options, requires
recursive servers to have to decide whether to probe to see if it is
the EDNS option or just EDNS that is causing the non response. In
the limited amount of time required to resolve a query before the
client times out this is not possible.
Similarly, incorrectly returning FORMERR to a EDNS option being
present, leads to the recursive server not being able to determine if
the server is just broken in the handling of the EDNS option or
doesn't support EDNS at all.
The consequences of servers not following the RFCs will only expand
if measures are not put in place to remove non compliant servers from
the ecosystem. Working around issues due to non RFC compliance is
not sustainable.
3. Common queries kinds that result in non responses.
There are a number common query kinds that fail to respond today.
They are: EDNS queries with and without extensions; queries for
unknown (unallocated) or unsupported types; and filtering of TCP
queries. queries.
2.1. Basic DNS Queries 3.1. Basic DNS Queries
2.1.1. Unknown / Unsupported Type Queries 3.1.1. Zone Existence
Initially to test existence of the zone, an SOA query should be made.
If the SOA record is not returned but some other response is
returned, this is a indication of a bad delegation. If the server
fails to get a response to a SOA query, the Operator should make an A
query for the zone, as some nameservers fail to respond to SOA
queries but will respond to A queries.
3.1.2. Unknown / Unsupported Type Queries
Identifying servers that fail to respond to unknown or unsupported Identifying servers that fail to respond to unknown or unsupported
types can be done by making an initial DNS query for an A record, types can be done by making an initial DNS query for an A record,
making a number of queries for an unallocated type, then making a making a number of queries for an unallocated type, then making a
query for an A record again. IANA maintains a registry of allocated query for an A record again. IANA maintains a registry of allocated
types. types.
If the server responds to the first and last queries but fails to If the server responds to the first and last queries but fails to
respond to the queries for the unallocated type, it is probably respond to the queries for the unallocated type, it is probably
faulty. The test should be repeated a number of times to eliminate faulty. The test should be repeated a number of times to eliminate
the likelihood of a false positive due to packet loss. the likelihood of a false positive due to packet loss.
2.1.2. DNS Flags 3.1.3. DNS Flags
Some servers fail to respond to DNS queries with various DNS flags Some servers fail to respond to DNS queries with various DNS flags
set, regardless of whether they are defined or still reserved. At set, regardless of whether they are defined or still reserved. At
the time of writing there are servers that fail to respond to queries the time of writing there are servers that fail to respond to queries
with the AD bit set to 1 and servers that fail to respond to queries with the AD bit set to 1 and servers that fail to respond to queries
with the last reserved flag bit set. with the last reserved flag bit set.
2.1.3. Unknown DNS opcodes 3.1.4. Unknown DNS opcodes
The use of previously undefined opcodes is to be expected. Since the The use of previously undefined opcodes is to be expected. Since the
DNS was first defined two new opcodes have been added, UPDATE and DNS was first defined two new opcodes have been added, UPDATE and
NOTIFY. NOTIFY.
NOTIMP is the expected rcode to an unknown / unimplemented opcode. NOTIMP is the expected rcode to an unknown or unimplemented opcode.
Note: while new opcodes will most probably use the current layout Note: while new opcodes will most probably use the current layout
structure for the rest of the message there is no requirement than structure for the rest of the message there is no requirement that
anything other than the DNS header match. anything other than the DNS header match.
2.1.4. TCP Queries 3.1.5. TCP Queries
All DNS servers are supposed to respond to queries over TCP All DNS servers are supposed to respond to queries over TCP
[RFC7766]. Firewalls that drop TCP connection attempts rather that [RFC7766]. Firewalls that drop TCP connection attempts, they should
resetting the connect attempt or send a ICMP/ICMPv6 administratively reset the connect attempt or send a ICMP/ICMPv6 administratively
prohibited message introduce excessive delays to the resolution prohibited message. Dropping TCP connections introduces excessive
process. delays to the resolution process.
Whether a server accepts TCP connections can be tested by first Whether a server accepts TCP connections can be tested by first
checking that it responds to UDP queries to confirm that it is up and checking that it responds to UDP queries to confirm that it is up and
operating, then attempting the same query over TCP. An additional operating, then attempting the same query over TCP. An additional
query should be made over UDP if the TCP connection attempt fails to query should be made over UDP if the TCP connection attempt fails to
confirm that the server under test is still operating. confirm that the server under test is still operating.
2.2. EDNS Queries 3.2. EDNS Queries
2.2.1. EDNS Queries - Version Independent 3.2.1. EDNS Queries - Version Independent
Identifying servers that fail to respond to EDNS queries can be done Identifying servers that fail to respond to EDNS queries can be done
by first identifying that the server responds to regular DNS queries, by first identifying that the server responds to regular DNS queries,
followed by a series of otherwise identical queries using EDNS, then followed by a series of otherwise identical queries using EDNS, then
making the original query again. A series of EDNS queries is needed making the original query again. A series of EDNS queries is needed
as at least one DNS implementation responds to the first EDNS query as at least one DNS implementation responds to the first EDNS query
with FORMERR but fails to respond to subsequent queries from the same with FORMERR but fails to respond to subsequent queries from the same
address for a period until a regular DNS query is made. The EDNS address for a period until a regular DNS query is made. The EDNS
query should specify a UDP buffer size of 512 bytes to avoid false query should specify a UDP buffer size of 512 bytes to avoid false
classification of not supporting EDNS due to response packet size. classification of not supporting EDNS due to response packet size.
If the server responds to the first and last queries but fails to If the server responds to the first and last queries but fails to
respond to most or all of the EDNS queries, it is probably faulty. respond to most or all of the EDNS queries, it is probably faulty.
The test should be repeated a number of times to eliminate the The test should be repeated a number of times to eliminate the
likelihood of a false positive due to packet loss. likelihood of a false positive due to packet loss.
Firewalls may also block larger EDNS responses but there is no easy Firewalls may also block larger EDNS responses but there is no easy
way to check authoritative servers to see if the firewall is way to check authoritative servers to see if the firewall is mis-
misconfigured. configured.
2.2.2. EDNS Queries - Version Specific 3.2.2. EDNS Queries - Version Specific
Some servers respond correctly to EDNS version 0 queries but fail to Some servers respond correctly to EDNS version 0 queries but fail to
respond to EDNS queries with version numbers that are higher than respond to EDNS queries with version numbers that are higher than
zero. Servers should respond with BADVERS to EDNS queries with zero. Servers should respond with BADVERS to EDNS queries with
version numbers that they do not support. version numbers that they do not support.
Some servers respond correctly to EDNS version 0 queries but fail to Some servers respond correctly to EDNS version 0 queries but fail to
set QR=1 when responding to EDNS versions they do not support. Such set QR=1 when responding to EDNS versions they do not support. Such
answers are discarded or treated as requests. answers are discarded or treated as requests.
2.2.3. EDNS Options 3.2.3. EDNS Options
Some servers fail to respond to EDNS queries with EDNS options set. Some servers fail to respond to EDNS queries with EDNS options set.
Unknown EDNS options are supposed to be ignored by the server Unknown EDNS options are supposed to be ignored by the server
[RFC6891]. [RFC6891].
2.2.4. EDNS Flags 3.2.4. EDNS Flags
Some servers fail to respond to EDNS queries with EDNS flags set. Some servers fail to respond to EDNS queries with EDNS flags set.
Server should ignore EDNS flags they do not understand and should not Server should ignore EDNS flags they do not understand and should not
add them to the response [RFC6891]. add them to the response [RFC6891].
3. Remediating 3.2.5. DNSSEC
Servers should be checked to see if they support DNSSEC. Servers
should also be checked to see if they support DNSSEC with EDNS.
4. Remediating
While the first step in remediating this problem is to get the While the first step in remediating this problem is to get the
offending nameserver code corrected, there is a very long tail offending nameserver code corrected, there is a very long tail
problem with DNS servers in that it can often take over a decade problem with DNS servers in that it can often take over a decade
between the code being corrected and a nameserver being upgraded with between the code being corrected and a nameserver being upgraded with
corrected code. With that in mind it is requested that TLD, and corrected code. With that in mind it is requested that TLD, and
other similar zone operators, take steps to identify and inform their other similar zone operators, take steps to identify and inform their
customers, directly or indirectly through registrars, that they are customers, directly or indirectly through registrars, that they are
running such servers and that the customers need to correct the running such servers and that the customers need to correct the
problem. problem.
skipping to change at page 8, line 22 skipping to change at page 9, line 22
audits to allow nameserver operators to test that they have correctly audits to allow nameserver operators to test that they have correctly
fixed their servers. Such tests should be rate limited to avoid fixed their servers. Such tests should be rate limited to avoid
these pages being a denial of service vector. these pages being a denial of service vector.
Nothing in this section precludes others testing servers for protocol Nothing in this section precludes others testing servers for protocol
compliance. DNS operators should test their servers to ensure that compliance. DNS operators should test their servers to ensure that
their vendors have shipped protocol compliant products. Nameserver their vendors have shipped protocol compliant products. Nameserver
vendors can use these tests as a part of this release processes. vendors can use these tests as a part of this release processes.
Registrants can use these tests to check their DNS operators servers. Registrants can use these tests to check their DNS operators servers.
4. Firewalls and Load Balancers 5. Firewalls and Load Balancers
Firewalls and load balancers can affect the externally visible Firewalls and load balancers can affect the externally visible
behaviour of a nameserver. Tests for conformance need to be done behaviour of a nameserver. Tests for conformance should to be done
from outside of any firewall so that the system as a whole is tested. from outside of any firewall so that the system as a whole is tested.
Firewalls and load balancers should not drop DNS packets that they Firewalls and load balancers should not drop DNS packets that they
don't understand. They should either pass through the packets or don't understand. They should either pass the packets or generate an
generate an appropriate error response. appropriate error response.
Requests for unknown query types is normal client behaviour and Requests for unknown query types is normal client behaviour and
should not be construed as an attack. Nameservers have always been should not be construed as an attack. Nameservers have always been
expected to be able to handle such queries. expected to be able to handle such queries.
Requests for unknown query classes is normal client behaviour and Requests for unknown query classes is normal client behaviour and
should not be construed as an attack. Nameservers have always been should not be construed as an attack. Nameservers have always been
expected to be able to handle such queries. expected to be able to handle such queries.
Requests with unknown opcodes is normal client behaviour and should Requests with unknown opcodes is normal client behaviour and should
not be construed as an attack. Nameservers have always been expected not be construed as an attack. Nameservers have always been expected
to be able to handle such queries. to be able to handle such queries.
Requests with unassigned flags set (DNS or EDNS) is expected client Requests with unassigned flags set (DNS or EDNS) is expected client
behaviour and should not be construed as an attack. The behaviour behaviour and should not be construed as an attack. The behaviour
for unassigned is to ignore them in the request and to not set them for unassigned flags is to ignore them in the request and to not set
in the response. All dropping DNS / EDNS packets with unassigned them in the response. Dropping DNS / EDNS packets with unassigned
flags does is make it harder to deploy extensions that make use of flags makes it difficult to deploy extensions that make use of them
them due to the need to reconfigure / update firewalls. due to the need to reconfigure and update firewalls.
Requests with unknown EDNS options is expected client behaviour and Requests with unknown EDNS options is expected client behaviour and
should not be construed as an attack. The correct behaviour for should not be construed as an attack. The correct behaviour for
unknown EDNS options is to ignore there presence when constructing a unknown EDNS options is to ignore there presence when constructing a
reply. reply.
Requests with unknown EDNS versions is expected client behaviour and Requests with unknown EDNS versions is expected client behaviour and
should not be construed as an attack. The correct behaviour for should not be construed as an attack. The correct behaviour for
unknown EDNS versions is to return BADVERS along with the highest unknown EDNS versions is to return BADVERS along with the highest
EDNS version the server supports. All dropping EDNS packets does is EDNS version the server supports. Dropping EDNS packet breaks EDNS
break EDNS version negotiation. version negotiation.
Firewalls should not assume that there will only be a single response Firewalls should not assume that there will only be a single response
message to a requests. There have been proposals to use EDNS to message to a requests. There have been proposals to use EDNS to
signal that multiple DNS messages be returned rather than a single signal that multiple DNS messages be returned rather than a single
UDP message that is fragmented at the IP layer. UDP message that is fragmented at the IP layer.
With the above said, there will be times when a nameserver mishandles However, there may be times when a nameserver mishandles messages
messages with a particular flag, EDNS option, EDNS version field, with a particular flag, EDNS option, EDNS version field, opcode, type
opcode, type or class field or combination there of to the point or class field or combination there of to the point where the
where the integrity of the nameserver is compromised. Firewalls integrity of the nameserver is compromised. Firewalls should offer
should have the ability to selectively reject messages with an the ability to selectively reject messages with an appropriately
appropriately constructed response based on all these fields while constructed response based on all these fields while awaiting a fix
awaiting a fix from the nameserver vendor. from the nameserver vendor.
DNS and EDNS in particular is designed to allow clients to be able to DNS and EDNS in particular is designed to allow clients to be able to
use new features against older servers without having to ask a use new features against older servers without having to validate
thousand questions to determine what the server supports which takes every option. Indiscriminate blocking of messages breaks that
time clients do not have. Indiscriminate blocking of messages breaks design.
that design.
5. Scrubbing Services 6. Scrubbing Services
Scrubbing services, like firewalls, can affect the externally visible Scrubbing services, like firewalls, can affect the externally visible
behaviour of a nameserver. If a operator uses a scrubbing service, behaviour of a nameserver. If a operator uses a scrubbing service,
they should check that legitimate queries are not being blocked. they should check that legitimate queries are not being blocked.
Scrubbing services, unlike firewalls, are also turned on and off in Scrubbing services, unlike firewalls, are also turned on and off in
response to denial of service attacks. One needs to take care when response to denial of service attacks. One needs to take care when
choosing a scrubbing service and ask questions like: choosing a scrubbing service and ask questions like mentioned above.
Do they pass unknown DNS query types?
Do they pass unknown EDNS versions?
Do they pass unknown EDNS options?
Do they pass unknown EDNS flags?
Do they pass requests with unknown DNS opcodes?
Do they pass requests with the remaining reserved DNS header flag
bit set?
None of these are attack vectors but some scrubbing services treat Ideally, Operators should run these tests against a scrubbing service
them as such. to ensure that these tests are not seen as attack vectors.
6. Whole Answer Caches 7. Whole Answer Caches
Whole answer caches take a previously constructed answer and return Whole answer caches take a previously constructed answer and return
it to a subsequent query for the same qname, qtype and qclass, just it to a subsequent query for the same qname, qtype and qclass, just
updating the query id field and possibly the qname to match the updating the query id field and possibly the qname to match the
incoming query to avoid constructing each response individually. incoming query to avoid constructing each response individually.
Whole answer caches can return the wrong response to a query if they Whole answer caches can return the wrong response to a query if they
do not take all of the attributes of the query into account, rather do not take all of the attributes of the query into account, rather
than just some of them e.g. qname, qtype and qclass. This has than just some of them e.g. qname, qtype and qclass. This has
implications when testing and with overall protocol compliance. implications when testing and with overall protocol compliance.
e.g. There are whole answer caches that ignore the EDNS version Two current examples are:
field which results in incorrect answers to non EDNS version 0
queries being returned if they were preceded by a EDNS version 0
query for the same name and type.
e.g. There are caches that ignore the EDNS options in the query Whole answer caches that ignore the EDNS version field which
resulting in options only working some of the time and/or options results in incorrect answers to non EDNS version 0 queries being
being returned when not requested. returned if they were preceded by a EDNS version 0 query for the
same name and type.
7. Response Code Selection Whole answer caches that ignore the EDNS options in the query
resulting in options only working some of the time and/or options
being returned when not requested.
Choosing the correct response code when fixing a nameserver is 8. Response Code Selection
important. Just because a type is not implemented does not mean that
NOTIMP is the correct response code to return. Response codes need
to be chosen considering how clients will handle them.
For unimplemented opcodes NOTIMP is the expected response code. Choosing the correct response code when responding to DNS queries is
Additionally a new opcode could change the message format by important. Just because a DNS qtype is not implemented does not mean
extending the header or changing the structure of the records etc. that NOTIMP is the correct response code to return. Response codes
This may result in FORMERR being returned though NOTIMP would be more should be chosen considering how clients will handle them.
correct.
In general, for unimplemented type codes Name Error (NXDOMAIN) and For unimplemented opcodes NOTIMP is the expected response code. For
NOERROR (no data) are the expected response codes. A server is not example, a new opcode could change the message format by extending
supposed to serve a zone which contains unsupported types ([RFC1034]) the header or changing the structure of the records etc. This may
so the only thing left is return if the QNAME exists or not. NOTIMP result in FORMERR being returned though NOTIMP would be more correct.
and REFUSED are not useful responses as they force the clients to try
all the authoritative servers for a zone looking for a server which
will answer the query.
Meta queries type may be the exception but these need to be thought Unimplemented type codes, Name Error (NXDOMAIN) and NOERROR (no data)
about on a case by case basis. are the expected response codes. A server is not supposed to serve a
zone which contains unsupported types ([RFC1034]) so the only thing
left is return if the QNAME exists or not. NOTIMP and REFUSED are
not useful responses as they force the clients to try the other
authoritative servers for a zone looking for a server which will
answer the query.
If the server supports EDNS and get a query with an unsupported EDNS Meta queries may be the exception but these need to be thought about
version, the correct response is BADVERS [RFC6891]. on a case by case basis.
If the server do not support EDNS at all, FORMERR and NOTIMP are the If the server supports EDNS and receives a query with an unsupported
expected error codes. That said a minimal EDNS server implementation EDNS version, the correct response is BADVERS [RFC6891].
just requires parsing the OPT records and responding with an empty
OPT record. There is no need to interpret any EDNS options present
in the request as unsupported options are expected to be ignored
[RFC6891].
8. Testing If the server does not support EDNS at all, FORMERR and NOTIMP are
the expected error codes. That said a minimal EDNS server
implementation requires parsing the OPT records and responding with
an empty OPT record. There is no need to interpret any EDNS options
present in the request as unsupported EDNS options are expected to be
ignored [RFC6891].
9. Testing
Testing is divided into two sections. Basic DNS which all servers Testing is divided into two sections. Basic DNS which all servers
should meet and Extended DNS which should be met by all servers that should meet and Extended DNS which should be met by all servers that
support EDNS (a server is deemed to support EDNS if it gives a valid support EDNS (a server is deemed to support EDNS if it gives a valid
EDNS response to any EDNS query). If a server does not support EDNS EDNS response to any EDNS query). If a server does not support EDNS
it should still respond to all the tests. it should still respond to all the tests.
It is advisable to run all of the tests below in parallel so as to It is advisable to run all of the tests below in parallel so as to
minimise the delays due to multiple timeouts when the servers do not minimise the delays due to multiple timeouts when the servers do not
respond. There are 16 queries directed to each nameserver assuming respond. There are 16 queries directed to each nameserver assuming
no packet loss testing different aspects of Basic DNS and EDNS. no packet loss testing different aspects of Basic DNS and EDNS.
The tests below use dig from BIND 9.11.0 which is still in The tests below use dig from BIND 9.11.0 which is still in
development. development.
8.1. Testing - Basic DNS 9.1. Testing - Basic DNS
This first set of tests cover basic DNS server behaviour and all This first set of tests cover basic DNS server behaviour and all
servers should pass these tests. servers should pass these tests.
8.1.1. Is The Server Configured For The Zone? 9.1.1. Is The Server Configured For The Zone?
Verify the server is configured for the zone: Verify the server is configured for the zone:
dig +noedns +noad +norec soa $zone @$server dig +noedns +noad +norec soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record expect: SOA record
expect: flag: aa to be present expect: flag: aa to be present
8.1.2. Testing Unknown Types? 9.1.2. Testing Unknown Types?
Check that queries for an unknown type work: Check that queries for an unknown type work:
dig +noedns +noad +norec type1000 $zone @$server dig +noedns +noad +norec type1000 $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: an empty answer section. expect: an empty answer section.
expect: flag: aa to be present expect: flag: aa to be present
That new types are to be expected is specified in Section 3.6, That new types are to be expected is specified in Section 3.6,
[RFC1035]. Servers that don't support a new type are expected to [RFC1035]. Servers that don't support a new type are expected to
reject a zone that contains a unsupported type as per Section 5.2, reject a zone that contains a unsupported type as per Section 5.2,
[RFC1035]. This means that a server that does load a zone can answer [RFC1035]. This means that a server that does load a zone can answer
questions for unknown types with NOERROR or NXDOMAIN as per questions for unknown types with NOERROR or NXDOMAIN as per
Section 4.3.2, [RFC1034]. [RFC6895] later reserved distinct ranges Section 4.3.2, [RFC1034]. [RFC6895] later reserved distinct ranges
for meta and data types which allows servers to be definitive about for meta and data types which allows servers to be definitive about
whether a query should be answerable from zone content or not. whether a query should be answerable from zone content or not.
8.1.3. Testing Header Bits 9.1.3. Testing Header Bits
8.1.3.1. Testing CD=1 Queries 9.1.3.1. Testing CD=1 Queries
Check that queries with CD=1 work: Check that queries with CD=1 work:
dig +noedns +noad +norec +cd soa $zone @$server dig +noedns +noad +norec +cd soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: flag: aa to be present expect: flag: aa to be present
CD use in queries is defined in [RFC4035]. CD use in queries is defined in [RFC4035].
8.1.3.2. Testing AD=1 Queries 9.1.3.2. Testing AD=1 Queries
Check that queries with AD=1 work: Check that queries with AD=1 work:
dig +noedns +norec +ad soa $zone @$server dig +noedns +norec +ad soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: flag: aa to be present expect: flag: aa to be present
AD use in queries is defined in [RFC6840]. AD use in queries is defined in [RFC6840].
8.1.3.3. Testing Reserved Bit 9.1.3.3. Testing Reserved Bit
Check that queries with the last unassigned DNS header flag work and Check that queries with the last unassigned DNS header flag work and
that the flag bit is not copied to the response: that the flag bit is not copied to the response:
dig +noedns +noad +norec +zflag soa $zone @$server dig +noedns +noad +norec +zflag soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: MBZ to not be in the response expect: MBZ to not be in the response
expect: flag: aa to be present expect: flag: aa to be present
MBZ (Must Be Zero) presence indicates the flag bit has been MBZ (Must Be Zero) presence indicates the flag bit has been
incorrectly copied. See Section 4.1.1, [RFC1035] "Z Reserved for incorrectly copied. See Section 4.1.1, [RFC1035] "Z Reserved for
future use. Must be zero in all queries and responses." future use. Must be zero in all queries and responses."
8.1.4. Testing Unknown Opcodes 9.1.4. Testing Unknown Opcodes
Check that new opcodes are handled: Check that new opcodes are handled:
dig +noedns +noad +opcode=15 +norec +header-only @$server dig +noedns +noad +opcode=15 +norec +header-only @$server
expect: status: NOTIMP expect: status: NOTIMP
expect: SOA record to not be present expect: SOA record to not be present
expect: flag: aa to NOT be present expect: flag: aa to NOT be present
As unknown opcodes have no definition, including packet format other As unknown opcodes have no definition, including packet format other
than there must be a DNS header present, there is only one possible than there must be a DNS header present, there is only one possible
rcode that make sense to return to a request with a unknown opcode rcode that make sense to return to a request with a unknown opcode
and that is NOTIMP. and that is NOTIMP.
8.1.5. Testing TCP 9.1.5. Testing TCP
Check that TCP queries work: Check that TCP queries work:
dig +noedns +noad +norec +tcp soa $zone @$server dig +noedns +noad +norec +tcp soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record expect: SOA record
expect: flag: aa to be present expect: flag: aa to be present
The requirement that TCP be supported is defined in [RFC7766]. The requirement that TCP be supported is defined in [RFC7766].
8.2. Testing - Extended DNS 9.2. Testing - Extended DNS
The next set of test cover various aspects of EDNS behaviour. If any The next set of test cover various aspects of EDNS behaviour. If any
of these tests succeed, then all of them should succeed. There are of these tests succeed, then all of them should succeed. There are
servers that support EDNS but fail to handle plain EDNS queries servers that support EDNS but fail to handle plain EDNS queries
correctly so a plain EDNS query is not a good indicator of lack of correctly so a plain EDNS query is not a good indicator of lack of
EDNS support. EDNS support.
8.2.1. Testing Minimal EDNS 9.2.1. Testing Minimal EDNS
Check that plain EDNS queries work: Check that plain EDNS queries work:
dig +nocookie +edns=0 +noad +norec soa $zone @$server dig +nocookie +edns=0 +noad +norec soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: OPT record to be present expect: OPT record to be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
+nocookie disables sending a EDNS COOKIE option in which is on by +nocookie disables sending a EDNS COOKIE option in which is on by
default. default.
8.2.2. Testing EDNS Version Negotiation 9.2.2. Testing EDNS Version Negotiation
Check that EDNS version 1 queries work (EDNS supported): Check that EDNS version 1 queries work (EDNS supported):
dig +nocookie +edns=1 +noednsneg +noad +norec soa $zone @$server dig +nocookie +edns=1 +noednsneg +noad +norec soa $zone @$server
expect: status: BADVERS expect: status: BADVERS
expect: SOA record to not be present expect: SOA record to not be present
expect: OPT record to be present expect: OPT record to be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to NOT be present expect: flag: aa to NOT be present
Only EDNS Version 0 is currently defined so the response should Only EDNS Version 0 is currently defined so the response should
always be a 0 version. This will change when EDNS version 1 is always be a 0 version. This will change when EDNS version 1 is
defined. BADVERS is the expected rcode if EDNS is supported as per defined. BADVERS is the expected rcode if EDNS is supported as per
Section 6.1.3, [RFC6891]. Section 6.1.3, [RFC6891].
8.2.3. Testing Unknown EDNS Options 9.2.3. Testing Unknown EDNS Options
Check that EDNS queries with an unknown option work (EDNS supported): Check that EDNS queries with an unknown option work (EDNS supported):
dig +nocookie +edns=0 +noad +norec +ednsopt=100 soa $zone @$server dig +nocookie +edns=0 +noad +norec +ednsopt=100 soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: OPT record to be present expect: OPT record to be present
expect: OPT=100 to not be present expect: OPT=100 to not be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
Unknown EDNS options are supposed to be ignored, Section 6.1.2, Unknown EDNS options are supposed to be ignored, Section 6.1.2,
[RFC6891]. [RFC6891].
8.2.4. Testing Unknown EDNS Flags 9.2.4. Testing Unknown EDNS Flags
Check that EDNS queries with unknown flags work (EDNS supported): Check that EDNS queries with unknown flags work (EDNS supported):
dig +nocookie +edns=0 +noad +norec +ednsflags=0x40 soa $zone @$server dig +nocookie +edns=0 +noad +norec +ednsflags=0x40 soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: OPT record to be present expect: OPT record to be present
expect: MBZ not to be present expect: MBZ not to be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
MBZ (Must Be Zero) presence indicates the flag bit has been MBZ (Must Be Zero) presence indicates the flag bit has been
incorrectly copied as per Section 6.1.4, [RFC6891]. incorrectly copied as per Section 6.1.4, [RFC6891].
8.2.5. Testing EDNS Version Negotiation With Unknown EDNS Flags 9.2.5. Testing EDNS Version Negotiation With Unknown EDNS Flags
Check that EDNS version 1 queries with unknown flags work (EDNS Check that EDNS version 1 queries with unknown flags work (EDNS
supported): supported):
dig +nocookie +edns=1 +noednsneg +noad +norec +ednsflags=0x40 soa \ dig +nocookie +edns=1 +noednsneg +noad +norec +ednsflags=0x40 soa \
$zone @$server $zone @$server
expect: status: BADVERS expect: status: BADVERS
expect: SOA record to NOT be present expect: SOA record to NOT be present
expect: OPT record to be present expect: OPT record to be present
expect: MBZ not to be present expect: MBZ not to be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to NOT be present expect: flag: aa to NOT be present
+noednsneg disables EDNS version negotiation in DiG; MBZ (Must Be +noednsneg disables EDNS version negotiation in DiG; MBZ (Must Be
Zero) presence indicates the flag bit has been incorrectly copied. Zero) presence indicates the flag bit has been incorrectly copied.
8.2.6. Testing EDNS Version Negotiation With Unknown EDNS Options 9.2.6. Testing EDNS Version Negotiation With Unknown EDNS Options
Check that EDNS version 1 queries with unknown options work (EDNS Check that EDNS version 1 queries with unknown options work (EDNS
supported): supported):
dig +nocookie +edns=1 +noednsneg +noad +norec +ednsopt=100 soa \ dig +nocookie +edns=1 +noednsneg +noad +norec +ednsopt=100 soa \
$zone @$server $zone @$server
expect: status: BADVERS expect: status: BADVERS
expect: SOA record to NOT be present expect: SOA record to NOT be present
expect: OPT record to be present expect: OPT record to be present
expect: OPT=100 to NOT be present expect: OPT=100 to NOT be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
+noednsneg disables EDNS version negotiation in DiG. +noednsneg disables EDNS version negotiation in DiG.
8.2.7. Testing DNSSEC Queries 9.2.7. Testing DNSSEC Queries
Check that a DNSSEC queries work (EDNS supported): Check that a DNSSEC queries work (EDNS supported):
dig +nocookie +edns=0 +noad +norec +dnssec soa $zone @$server dig +nocookie +edns=0 +noad +norec +dnssec soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: OPT record to be present expect: OPT record to be present
expect: DO=1 to be present if a RRSIG is in the response expect: DO=1 to be present if a RRSIG is in the response
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
DO=1 should be present if RRSIGs are returned as they indicate that DO=1 should be present if RRSIGs are returned as they indicate that
the server supports DNSSEC. Servers that support DNSSEC are supposed the server supports DNSSEC. Servers that support DNSSEC are supposed
to copy the DO bit from the request to the response as per [RFC3225]. to copy the DO bit from the request to the response as per [RFC3225].
8.2.8. Testing EDNS Version Negotiation With DNSSEC 9.2.8. Testing EDNS Version Negotiation With DNSSEC
Check that EDNS version 1 DNSSEC queries work (EDNS supported): Check that EDNS version 1 DNSSEC queries work (EDNS supported):
dig +nocookie +edns=1 +noednsneg +noad +norec +dnssec soa \ dig +nocookie +edns=1 +noednsneg +noad +norec +dnssec soa \
$zone @$server $zone @$server
expect: status: BADVERS expect: status: BADVERS
expect: SOA record to not be present expect: SOA record to not be present
expect: OPT record to be present expect: OPT record to be present
expect: DO=1 to be present if the EDNS version 0 DNSSEC query test expect: DO=1 to be present if the EDNS version 0 DNSSEC query test
returned DO=1 returned DO=1
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to NOT be present expect: flag: aa to NOT be present
+noednsneg disables EDNS version negotiation in DiG. +noednsneg disables EDNS version negotiation in DiG.
8.2.9. Testing With Multiple Defined EDNS Options 9.2.9. Testing With Multiple Defined EDNS Options
Check that EDNS queries with multiple defined EDNS options work: Check that EDNS queries with multiple defined EDNS options work:
dig +edns=0 +noad +norec +cookie +nsid +expire +subnet=0.0.0.0/0 \ dig +edns=0 +noad +norec +cookie +nsid +expire +subnet=0.0.0.0/0 \
soa $zone @$server soa $zone @$server
expect: status: NOERROR expect: status: NOERROR
expect: SOA record to be present expect: SOA record to be present
expect: OPT record to be present expect: OPT record to be present
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
8.2.10. When EDNS Is Not Supported 9.3. When EDNS Is Not Supported
If EDNS is not supported by the nameserver, we expect a response to If EDNS is not supported by the nameserver, we expect a response to
all the above queries. That response may be a FORMERR or NOTIMP all the above queries. That response may be a FORMERR or NOTIMP
error response or the OPT record may just be ignored. error response or the OPT record may just be ignored.
Some nameservers only return a EDNS response when a particular EDNS Some nameservers only return a EDNS response when a particular EDNS
option or flag (e.g. DO=1) is present in the request. This option or flag (e.g. DO=1) is present in the request. This
behaviour is not compliant behaviour and may hide other incorrect behaviour is not compliant behaviour and may hide other incorrect
behaviour from the above tests. Re-testing with the triggering behaviour from the above tests. Re-testing with the triggering
option / flag present will expose this misbehaviour. option / flag present will expose this misbehaviour.
9. Security Considerations 10. Security Considerations
Testing protocol compliance can potentially result in false reports Testing protocol compliance can potentially result in false reports
of attempts to break services from Intrusion Detection Services and of attempts to break services from Intrusion Detection Services and
firewalls. None of the tests listed above should break nominally firewalls. None of the tests listed above should break nominally
EDNS compliant servers. None of the tests above should break non EDNS compliant servers. None of the tests above should break non
EDNS servers. All the tests above are well formed, though not EDNS servers. All the tests above are well formed, though not
necessarily common, DNS queries. necessarily common, DNS queries.
Relaxing firewall settings to ensure EDNS compliance could Relaxing firewall settings to ensure EDNS compliance could
potentially expose a critical implementation flaw in the nameserver. potentially expose a critical implementation flaw in the nameserver.
Nameservers should be tested for conformance before relaxing firewall Nameservers should be tested for conformance before relaxing firewall
settings. settings.
When removing delegations for non-compliant servers there can be a When removing delegations for non-compliant servers there can be a
knock on effect on other zones that require these zones to be knock on effect on other zones that require these zones to be
operational for the nameservers addresses to be resolved. operational for the nameservers addresses to be resolved.
10. IANA Considerations 11. IANA Considerations
There are no actions for IANA. There are no actions for IANA.
11. References 12. References
11.1. Normative References 12.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>. <http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
skipping to change at page 19, line 10 skipping to change at page 19, line 45
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <http://www.rfc-editor.org/info/rfc6895>. April 2013, <http://www.rfc-editor.org/info/rfc6895>.
[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and [RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
D. Wessels, "DNS Transport over TCP - Implementation D. Wessels, "DNS Transport over TCP - Implementation
Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
<http://www.rfc-editor.org/info/rfc7766>. <http://www.rfc-editor.org/info/rfc7766>.
11.2. Informative References 12.2. Informative References
[RFC1033] Lottor, M., "Domain Administrators Operations Guide", [RFC1033] Lottor, M., "Domain Administrators Operations Guide",
RFC 1033, DOI 10.17487/RFC1033, November 1987, RFC 1033, DOI 10.17487/RFC1033, November 1987,
<http://www.rfc-editor.org/info/rfc1033>. <http://www.rfc-editor.org/info/rfc1033>.
Author's Address Author's Address
M. Andrews M. Andrews
Internet Systems Consortium Internet Systems Consortium
950 Charter Street 950 Charter Street
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