draft-ietf-dnsop-no-response-issue-05.txt   draft-ietf-dnsop-no-response-issue-06.txt 
Network Working Group M. Andrews Network Working Group M. Andrews
Internet-Draft ISC Internet-Draft ISC
Intended status: Best Current Practice September 18, 2016 Intended status: Best Current Practice October 27, 2016
Expires: March 22, 2017 Expires: April 30, 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-05 draft-ietf-dnsop-no-response-issue-06
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 which This document identifies a number of common kinds of queries to 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 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
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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 March 22, 2017. This Internet-Draft will expire on April 30, 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Common queries kinds that result in non responses. . . . . . 4 3. Common queries kinds that result in non responses. . . . . . 5
3.1. Basic DNS Queries . . . . . . . . . . . . . . . . . . . . 5 3.1. Basic DNS Queries . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Zone Existence . . . . . . . . . . . . . . . . . . . 5 3.1.1. Zone Existence . . . . . . . . . . . . . . . . . . . 5
3.1.2. Unknown / Unsupported Type Queries . . . . . . . . . 5 3.1.2. Unknown / Unsupported Type Queries . . . . . . . . . 5
3.1.3. DNS Flags . . . . . . . . . . . . . . . . . . . . . . 5 3.1.3. DNS Flags . . . . . . . . . . . . . . . . . . . . . . 6
3.1.4. Unknown DNS opcodes . . . . . . . . . . . . . . . . . 5 3.1.4. Unknown DNS opcodes . . . . . . . . . . . . . . . . . 6
3.1.5. TCP Queries . . . . . . . . . . . . . . . . . . . . . 6 3.1.5. Recursive Queries . . . . . . . . . . . . . . . . . . 6
3.1.6. TCP Queries . . . . . . . . . . . . . . . . . . . . . 6
3.2. EDNS Queries . . . . . . . . . . . . . . . . . . . . . . 6 3.2. EDNS Queries . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. EDNS Queries - Version Independent . . . . . . . . . 6 3.2.1. EDNS Queries - Version Independent . . . . . . . . . 7
3.2.2. EDNS Queries - Version Specific . . . . . . . . . . . 6 3.2.2. EDNS Queries - Version Specific . . . . . . . . . . . 7
3.2.3. EDNS Options . . . . . . . . . . . . . . . . . . . . 7 3.2.3. EDNS Options . . . . . . . . . . . . . . . . . . . . 7
3.2.4. EDNS Flags . . . . . . . . . . . . . . . . . . . . . 7 3.2.4. EDNS Flags . . . . . . . . . . . . . . . . . . . . . 7
3.2.5. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.5. Truncated EDNS Responses . . . . . . . . . . . . . . 8
4. Remediating . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.6. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 8
5. Firewalls and Load Balancers . . . . . . . . . . . . . . . . 9 3.2.7. EDNS over TCP . . . . . . . . . . . . . . . . . . . . 8
6. Scrubbing Services . . . . . . . . . . . . . . . . . . . . . 10 4. Firewalls and Load Balancers . . . . . . . . . . . . . . . . 8
7. Whole Answer Caches . . . . . . . . . . . . . . . . . . . . . 10 5. Scrubbing Services . . . . . . . . . . . . . . . . . . . . . 9
8. Response Code Selection . . . . . . . . . . . . . . . . . . . 11 6. Whole Answer Caches . . . . . . . . . . . . . . . . . . . . . 9
9. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. Response Code Selection . . . . . . . . . . . . . . . . . . . 10
9.1. Testing - Basic DNS . . . . . . . . . . . . . . . . . . . 12 8. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1.1. Is The Server Configured For The Zone? . . . . . . . 12 8.1. Testing - Basic DNS . . . . . . . . . . . . . . . . . . . 11
9.1.2. Testing Unknown Types? . . . . . . . . . . . . . . . 12 8.1.1. Is The Server Configured For The Zone? . . . . . . . 11
9.1.3. Testing Header Bits . . . . . . . . . . . . . . . . . 13 8.1.2. Testing Unknown Types? . . . . . . . . . . . . . . . 11
9.1.4. Testing Unknown Opcodes . . . . . . . . . . . . . . . 14 8.1.3. Testing Header Bits . . . . . . . . . . . . . . . . . 12
9.1.5. Testing TCP . . . . . . . . . . . . . . . . . . . . . 14 8.1.4. Testing Unknown Opcodes . . . . . . . . . . . . . . . 13
9.2. Testing - Extended DNS . . . . . . . . . . . . . . . . . 14 8.1.5. Testing Rescursive Queries . . . . . . . . . . . . . 13
9.2.1. Testing Minimal EDNS . . . . . . . . . . . . . . . . 15 8.1.6. Testing TCP . . . . . . . . . . . . . . . . . . . . . 14
9.2.2. Testing EDNS Version Negotiation . . . . . . . . . . 15 8.2. Testing - Extended DNS . . . . . . . . . . . . . . . . . 14
9.2.3. Testing Unknown EDNS Options . . . . . . . . . . . . 15 8.2.1. Testing Minimal EDNS . . . . . . . . . . . . . . . . 14
9.2.4. Testing Unknown EDNS Flags . . . . . . . . . . . . . 16 8.2.2. Testing EDNS Version Negotiation . . . . . . . . . . 14
9.2.5. Testing EDNS Version Negotiation With Unknown EDNS 8.2.3. Testing Unknown EDNS Options . . . . . . . . . . . . 15
8.2.4. Testing Unknown EDNS Flags . . . . . . . . . . . . . 15
8.2.5. Testing EDNS Version Negotiation With Unknown EDNS
Flags . . . . . . . . . . . . . . . . . . . . . . . . 16 Flags . . . . . . . . . . . . . . . . . . . . . . . . 16
9.2.6. Testing EDNS Version Negotiation With Unknown EDNS 8.2.6. Testing EDNS Version Negotiation With Unknown EDNS
Options . . . . . . . . . . . . . . . . . . . . . . . 16 Options . . . . . . . . . . . . . . . . . . . . . . . 16
9.2.7. Testing DNSSEC Queries . . . . . . . . . . . . . . . 17
9.2.8. Testing EDNS Version Negotiation With DNSSEC . . . . 17
9.2.9. Testing With Multiple Defined EDNS Options . . . . . 18
9.3. When EDNS Is Not Supported . . . . . . . . . . . . . . . 18 8.2.7. Testing DNSSEC Queries . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8.2.8. Testing EDNS Version Negotiation With DNSSEC . . . . 17
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 8.2.9. Testing With Multiple Defined EDNS Options . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 8.3. When EDNS Is Not Supported . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 19 9. Remediation . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. Normative References . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
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 Failure to respond to a query is indistinguishable from a packet loss
loss. Without doing a analysis of query response patterns will without doing a analysis of query response patterns. Additionally
results in unnecessary additional queries being made by DNS clients, failure to respond results in unnecessary queries being made by DNS
and delays being introduced to the resolution process. clients, 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.
Servers which fail to respond to queries to remain results in Servers which fail to respond to queries results in developers being
developers being hesitant to deploy new standards. Such servers need hesitant to deploy new standards. Such servers need to be
to be identified. identified.
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. There should be no need to drop queries because a
nameserver does not understand 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. Additionally, the nameserver should not assume that directed to it. Additionally, the nameserver should not assume that
there isn't a delegation to the server even if it is not configured there isn't a delegation to the server even if it is not configured
to serve the zone. Broken nameservers are a common occurrence in the to serve the zone. Broken nameservers are a common occurrence in the
DNS and receiving queries for zones that the server is not configured DNS and receiving queries for zones that the server is not configured
for is not necessarily an indication that the server is under attack. for is not necessarily an indication that the server is under attack.
Parent zone operators are supposed to regularly check that the Parent zone operators are supposed to regularly check that the
delegating NS records are consistent with those of the delegated zone delegating NS records are consistent with those of the delegated zone
and to correct them when they are not [RFC1034]. Doing this and to correct them when they are not [RFC1034]. Doing this
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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. Misclassification of server behaviour is unavoidable
unavoidable when rate limiting is done. when rate limiting is used until the population of servers which fail
to respond to well formed queries drops to near zero.
2. Consequences 2. Consequences
Lack of following the relevant RFCs has lead to various consequences. Not following the relevant DNS RFCs has multiple adverse
Some as a direct result and some from recursive servers try to work consequences. Some resulting directly from the non-compliant
around the non compliance. Fixing known issues know will reduce behaviour and others as a result of work-arounds forced on recursive
future consequences as DNS clients make use of the features available servers. Addressing known issues now will reduce future
in the DNS protocol. interoperability issues as the DNS protocol continues to evolve and
clients make use of newly introduced DNS features.
The AD flag bit in a response cannot be trusted to mean anything as Some examples of known consequences include:
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 o The AD flag bit in a response cannot be trusted to mean anything
servers having to assume EDNS may not supported and fallback to plain as many servers incorrectly copied the flag bit from the request
DNS is required. Servers get incorrectly diagnosed as not supporting to the response despite the prohibition.
EDNS and when they also serve signed zones DNSSEC validation fails.
Similarly, wide spread non response to EDNS options, requires o Widespread non response to EDNS queries has lead to recursive
recursive servers to have to decide whether to probe to see if it is servers having to assume EDNS may not supported and that fallback
the EDNS option or just EDNS that is causing the non response. In to plain DNS is required. Servers get incorrectly diagnosed as
the limited amount of time required to resolve a query before the not supporting EDNS and when they also serve signed zones DNSSEC
client times out this is not possible. validation fails.
Similarly, incorrectly returning FORMERR to a EDNS option being o Widespread non response to EDNS options, requires recursive
present, leads to the recursive server not being able to determine if servers to have to decide whether to probe to see if it is the
the server is just broken in the handling of the EDNS option or EDNS option or just EDNS that is causing the non response. In the
doesn't support EDNS at all. limited amount of time required to resolve a query before the
client times out this is not possible.
The consequences of servers not following the RFCs will only expand o Incorrectly returning FORMERR to a EDNS option being present,
if measures are not put in place to remove non compliant servers from 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.
o Mishandling of unknown query types has contributed to the
abandoning of the transition of the SPF type.
o Mishandling of unknown query types has slowed up the development
of DANE and and result in additional rules being specified to
reduce the probability of interacting with a broken server when
making TLSA queries.
The consequences of servers not following the RFCs will only grow if
measures are not put in place to remove non compliant servers from
the ecosystem. Working around issues due to non RFC compliance is the ecosystem. Working around issues due to non RFC compliance is
not sustainable. not sustainable.
Most, if not all, of these consequences could have been avoided if
action had been taken to remove non compliant servers as soon as
people were aware of them. To actively seek out broken
implementations and servers and inform their developers and operators
that they need to fix their servers.
3. Common queries kinds that result in non responses. 3. Common queries kinds that result in non responses.
There are a number common query kinds that fail to respond today. There are a number common query kinds that fail to respond today.
They are: EDNS queries with and without extensions; queries for They are: EDNS queries with and without extensions; queries for
unknown (unallocated) or unsupported types; and filtering of TCP unknown (unallocated) or unsupported types; and filtering of TCP
queries. queries.
3.1. Basic DNS Queries 3.1. Basic DNS Queries
3.1.1. Zone Existence 3.1.1. Zone Existence
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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 or 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 that 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.
3.1.5. TCP Queries 3.1.5. Recursive Queries
A non-recursive server is supposed to respond to recursive queries as
if the RD bit is not set.
3.1.6. 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, they should [RFC7766]. Firewalls that drop TCP connection attempts, they should
reset the connect attempt or send a ICMP/ICMPv6 administratively reset the connect attempt or send a ICMP/ICMPv6 administratively
prohibited message. Dropping TCP connections introduces excessive prohibited message. Dropping TCP connections introduces excessive
delays to the resolution 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
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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].
3.2.4. 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].
3.2.5. DNSSEC 3.2.5. Truncated EDNS Responses
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
offending nameserver code corrected, there is a very long tail
problem with DNS servers in that it can often take over a decade
between the code being corrected and a nameserver being upgraded with
corrected code. With that in mind it is requested that TLD, and
other similar zone operators, take steps to identify and inform their
customers, directly or indirectly through registrars, that they are
running such servers and that the customers need to correct the
problem.
TLD operators are being asked to do this as they, due to the nature
of running a TLD and the hierarchical nature of the DNS, have access
to a large numbers of nameserver names as well as contact details for
the registrants of those nameservers. While it is possible to
construct lists of nameservers from other sources, and that has been
done to survey the state of the Internet, that doesn't give the
tester the contact details necessary to inform the operators. The
SOA RNAME is often invalid and whois data is obscured and / or not
available which makes it infeasible for others to do this.
While this section talks about TLD operators performing this work, it
may be done by registrars on behalf of the TLD operator. The intent
is to ensure that the testing happens and that operators of non-
compliant nameservers be informed, rather than to prescribe who does
the actual testing and communication. Note: having registrars
perform this testing and reporting is likely to result in duplicate
reports for the same server being issued by multiple registrars.
TLD operators should construct a list of servers child zones are
delegated to along with a delegated zone name. This name shall be
the query name used to test the server as it is supposed to exist.
For each server the TLD operator shall make an SOA query of the
delegated zone name. This should result in the SOA record being
returned in the answer section. If the SOA record is not returned
but some other response is returned, this is a indication of a bad
delegation and the TLD operator should take whatever steps it
normally takes to rectify a bad delegation. If more that one zone is
delegated to the server, it should choose another zone until it finds
a zone which responds correctly or it exhausts the list of zones
delegated to the server.
If the server fails to get a response to a SOA query, the TLD
operator should make an A query as some nameservers fail to respond
to SOA queries but respond to A queries. If it gets no response to
the A query, another delegated zone should be queried for as some
nameservers fail to respond to zones they are not configured for. If
subsequent queries find a responding zone, all delegation to this
server need to be checked and rectified using the TLD's normal
procedures.
Having identified a working <server, query name> tuple the TLD
operator should now check that the server responds to EDNS, Unknown
Query Type and TCP tests as described above. If the TLD operator
finds that server fails any of the tests, the TLD operator shall take
steps to inform the operator of the server that they are running a
faulty nameserver and that they need to take steps to correct the
matter. The TLD operator shall also record the <server, query name>
for follow-up testing.
If repeated attempts to inform and get the customer to correct / Some EDNS aware servers fail to include a OPT record when a truncated
replace the faulty server are unsuccessful the TLD operator shall response is sent. A OPT record is supposed to be included in a
remove all delegations to said server from the zone. Removal of truncated response [RFC6891].
delegations is the step of last resort in handling complaints as
specified in [RFC1033] COMPLAINTS.
It will also be necessary for TLD operators to repeat the scans Some EDNS aware server fail to honour the advertised EDNS buffer size
periodically. It is recommended that this be performed monthly and send over sized responses.
backing off to bi-annually once the numbers of faulty servers found
drops off to less than 1 in 100000 servers tested. Follow-up tests
for faulty servers still need to be performed monthly.
Some operators claim that they can't perform checks at registration 3.2.6. DNSSEC
time. If a check is not performed at registration time, it needs to
be performed within a week of registration in order to detect faulty
servers swiftly.
Checking of delegations by TLD operators should be nothing new as Servers should be checked to see if they support DNSSEC. Servers
they have been required from the very beginnings of DNS to do this should also be checked to see if they support DNSSEC with EDNS.
[RFC1034]. Checking for compliance of nameserver operations should
just be a extension of such testing.
It is recommended that TLD operators setup a test web page which 3.2.7. EDNS over TCP
performs the tests the TLD operator performs as part of their regular
audits to allow nameserver operators to test that they have correctly
fixed their servers. Such tests should be rate limited to avoid
these pages being a denial of service vector.
Nothing in this section precludes others testing servers for protocol Some EDNS aware servers incorrectly limit the TCP response sizes to
compliance. DNS operators should test their servers to ensure that the advertised UDP response size.
their vendors have shipped protocol compliant products. Nameserver
vendors can use these tests as a part of this release processes.
Registrants can use these tests to check their DNS operators servers.
5. Firewalls and Load Balancers 4. 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 should 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 the packets or generate an don't understand. They should either pass the packets or 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
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integrity of the nameserver is compromised. Firewalls should offer integrity of the nameserver is compromised. Firewalls should offer
the ability to selectively reject messages with an appropriately the ability to selectively reject messages with an appropriately
constructed response based on all these fields while awaiting a fix constructed response based on all these fields while 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 validate use new features against older servers without having to validate
every option. Indiscriminate blocking of messages breaks that every option. Indiscriminate blocking of messages breaks that
design. design.
6. Scrubbing Services 5. 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 mentioned above. choosing a scrubbing service and ask questions like mentioned above.
Ideally, Operators should run these tests against a scrubbing service Ideally, Operators should run these tests against a scrubbing service
to ensure that these tests are not seen as attack vectors. to ensure that these tests are not seen as attack vectors.
7. Whole Answer Caches 6. 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.
Two current examples are: Two current examples are:
Whole answer caches that ignore the EDNS version field which o Whole answer caches that ignore the EDNS version field which
results in incorrect answers to non EDNS version 0 queries being results in incorrect answers to non EDNS version 0 queries being
returned if they were preceded by a EDNS version 0 query for the returned if they were preceded by a EDNS version 0 query for the
same name and type. same name and type.
Whole answer caches that ignore the EDNS options in the query o Whole answer caches that ignore the EDNS options in the query
resulting in options only working some of the time and/or options resulting in options only working some of the time and/or options
being returned when not requested. being returned when not requested.
8. Response Code Selection 7. Response Code Selection
Choosing the correct response code when responding to DNS queries is Choosing the correct response code when responding to DNS queries is
important. Just because a DNS qtype is not implemented does not mean important. Just because a DNS qtype is not implemented does not mean
that NOTIMP is the correct response code to return. Response codes that NOTIMP is the correct response code to return. Response codes
should be chosen considering how clients will handle them. should be chosen considering how clients will handle them.
For unimplemented opcodes NOTIMP is the expected response code. For For unimplemented opcodes NOTIMP is the expected response code. For
example, a new opcode could change the message format by extending example, a new opcode could change the message format by extending
the header or changing the structure of the records etc. This may the header or changing the structure of the records etc. This may
result in FORMERR being returned though NOTIMP would be more correct. result in FORMERR being returned though NOTIMP would be more correct.
skipping to change at page 12, line 5 skipping to change at page 11, line 5
If the server supports EDNS and receives a query with an unsupported If the server supports EDNS and receives a query with an unsupported
EDNS version, the correct response is BADVERS [RFC6891]. EDNS version, the correct response is BADVERS [RFC6891].
If the server does not support EDNS at all, FORMERR and NOTIMP are If the server does not support EDNS at all, FORMERR and NOTIMP are
the expected error codes. That said a minimal EDNS server the expected error codes. That said a minimal EDNS server
implementation requires parsing the OPT records and responding with implementation requires parsing the OPT records and responding with
an empty OPT record. There is no need to interpret any EDNS options 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 present in the request as unsupported EDNS options are expected to be
ignored [RFC6891]. ignored [RFC6891].
9. Testing 8. 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.
development.
9.1. Testing - Basic DNS 8.1. 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.
9.1.1. Is The Server Configured For The Zone? 8.1.1. 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: the SOA record to be present in the answer section
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT be present
expect: the OPT record to NOT be present
9.1.2. Testing Unknown Types? 8.1.2. 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
expect: flag: ad to NOT be present
expect: the OPT record to NOT 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.
9.1.3. Testing Header Bits 8.1.3. Testing Header Bits
9.1.3.1. Testing CD=1 Queries 8.1.3.1. 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: the SOA record to be present in the answer section
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT be present
expect: the OPT record to NOT be present
CD use in queries is defined in [RFC4035]. CD use in queries is defined in [RFC4035].
9.1.3.2. Testing AD=1 Queries 8.1.3.2. 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: the SOA record to be present in the answer section
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT be present
expect: the OPT record to NOT be present
AD use in queries is defined in [RFC6840]. AD use in queries is defined in [RFC6840].
9.1.3.3. Testing Reserved Bit 8.1.3.3. 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: the SOA record to be present in the answer section
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
expect: flag: ad to NOT be present
expect: the OPT record to NOT 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."
9.1.4. Testing Unknown Opcodes 8.1.4. 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
expect: flag: ad to NOT be present
expect: the OPT record 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.
9.1.5. Testing TCP 8.1.5. Testing Rescursive Queries
Check that recursive queries work:
dig +noedns +noad +rec soa $zone @$server
expect: status: NOERROR
expect: the SOA record to be present in the answer section
expect: flag: aa to be present
expect: flag: ad to NOT be present
expect: flag: rd to be present
expect: the OPT record to NOT be present
8.1.6. 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: the SOA record to be present in the answer section
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT be present
expect: the OPT record to NOT be present
The requirement that TCP be supported is defined in [RFC7766]. The requirement that TCP be supported is defined in [RFC7766].
9.2. Testing - Extended DNS 8.2. 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.
9.2.1. Testing Minimal EDNS 8.2.1. 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: the SOA record to be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT 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.
9.2.2. Testing EDNS Version Negotiation 8.2.2. 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: the SOA record to NOT be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
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
expect: flag: ad 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].
9.2.3. Testing Unknown EDNS Options 8.2.3. 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: the SOA record to be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
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
expect: flag: ad to NOT 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].
9.2.4. Testing Unknown EDNS Flags 8.2.4. 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: the SOA record to be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
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
expect: flag: ad to NOT 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].
9.2.5. Testing EDNS Version Negotiation With Unknown EDNS Flags 8.2.5. 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: a OPT record to be present in the additional section
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
expect: flag: ad 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.
9.2.6. Testing EDNS Version Negotiation With Unknown EDNS Options 8.2.6. 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: a OPT record to be present in the additional section
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
expect: flag: ad to NOT be present
+noednsneg disables EDNS version negotiation in DiG. +noednsneg disables EDNS version negotiation in DiG.
9.2.7. Testing DNSSEC Queries 8.2.7. 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: the SOA record to be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
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].
9.2.8. Testing EDNS Version Negotiation With DNSSEC 8.2.8. 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: a OPT record to be present in the additional section
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.
9.2.9. Testing With Multiple Defined EDNS Options 8.2.9. 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: the SOA record to be present in the answer section
expect: OPT record to be present expect: a OPT record to be present in the additional section
expect: EDNS Version 0 in response expect: EDNS Version 0 in response
expect: flag: aa to be present expect: flag: aa to be present
expect: flag: ad to NOT be present
9.3. When EDNS Is Not Supported 8.3. 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. Remediation
Name server operators are generally expected to test their own
infrastructure for compliance to standards. The above tests should
be run when new systems are brought online, and should be repeated
periodically to ensure continued interoperability.
Domain registrants who do not maintain their own DNS infrastructure
are entitled to a DNS service that conforms to standards and
interoperates well. Registrants who become aware that their DNS
operator does not have a well maintained or compliant infrastructure
should insist that their service provider correct issues, and switch
providers if they do not.
In the event that an operator experiences problems due to the
behaviour of name servers outside their control, the above tests will
help in narrowing down the precise issue(s) which can then be
reported to the relevant party.
If contact information for the operator of a misbehaving name server
is not already known, the following methods of communication could be
considered:
o the RNAME of the zone authoritative for the name of the
misbehaving server
o the RNAME of zones for which the offending server is authoritative
o administrative or technical contacts listed in the registration
information for the parent domain of the name of the misbehaving
server, or for zones for which the name server is authoritative
o the registrar or registry for such zones
o DNS-specific operational fora (e.g. mailing lists)
Operators of parent zones may wish to regularly test the
authoritative name servers of their child zones. However, parent
operators can have widely varying capabilities in terms of
notification or remediation depending on whether they have a direct
relationship with the child operator. Many TLD registries, for
example, cannot directly contact their registrants and may instead
need to communicate through the relevant registrar. In such cases
it may be most efficient for registrars to take on the responsibility
for testing the name servers of their registrants, since they have a
direct relationship.
When notification is not effective at correcting problems with a
misbehaving name server, parent operators can choose to remove NS
record sets (and glue records below) that refer to the faulty server.
This should only be done as a last resort and with due consideration,
as removal of a delegation can have unanticipated side effects. For
example, other parts of the DNS tree may depend on names below the
removed zone cut, and the parent operator may find themselves
responsible for causing new DNS failures to occur.
10. 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
skipping to change at page 19, line 5 skipping to change at page 20, line 27
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.
11. IANA Considerations 11. IANA Considerations
There are no actions for IANA. There are no actions for IANA.
12. References 12. 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 45 skipping to change at page 21, line 19
[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>.
12.2. Informative References
[RFC1033] Lottor, M., "Domain Administrators Operations Guide",
RFC 1033, DOI 10.17487/RFC1033, November 1987,
<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
Redwood City, CA 94063 Redwood City, CA 94063
US US
Email: marka@isc.org Email: marka@isc.org
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