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DNS Operations M. Larson
Internet-Draft P. Barber
Expires: August 16, 2004 VeriSign
February 16, 2004
Observed DNS Resolution Misbehavior
draft-ietf-dnsop-bad-dns-res-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 16, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This Internet-Draft describes DNS name server and resolver behavior
that results in a significant query volume sent to the root and
top-level domain (TLD) name servers. In some cases we recommend
minor additions to the DNS protocol specification and corresponding
changes in name server implementations to alleviate these unnecessary
queries. The recommendations made in this document are a direct
byproduct of observation and analysis of abnormal query traffic
patterns seen at two of the thirteen root name servers and all
thirteen com/net TLD name servers.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in RFC 2119 [1].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Observed name server misbehavior . . . . . . . . . . . . . 4
2.1 Aggressive requerying for delegation information . . . . . 4
2.1.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Repeated queries to lame servers . . . . . . . . . . . . . 5
2.2.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Inability to follow multiple levels of out-of-zone glue . 6
2.3.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Aggressive retransmission when fetching glue . . . . . . . 7
2.4.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 8
2.5 Aggressive retransmission behind firewalls . . . . . . . . 8
2.5.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 8
2.6 Misconfigured NS records . . . . . . . . . . . . . . . . . 9
2.6.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 10
2.7 Name server records with zero TTL . . . . . . . . . . . . 10
2.7.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 11
2.8 Unnecessary dynamic update messages . . . . . . . . . . . 11
2.8.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 11
2.9 Queries for domain names resembling IP addresses . . . . . 12
2.9.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 12
2.10 Misdirected recursive queries . . . . . . . . . . . . . . 12
2.10.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 13
2.11 Suboptimal name server selection algorithm . . . . . . . . 13
2.11.1 Recommendation . . . . . . . . . . . . . . . . . . . . . . 13
3. IANA considerations . . . . . . . . . . . . . . . . . . . 15
4. Security considerations . . . . . . . . . . . . . . . . . 16
5. Internationalization considerations . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . 19
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1. Introduction
Observation of query traffic received by two root name servers and
the thirteen com/net TLD name servers has revealed that a large
proportion of the total traffic often consists of "requeries". A
requery is the same question (<qname, qtype, qclass>) asked
repeatedly at an unexpectedly high rate. We have observed requeries
from both a single IP address and multiple IP addresses.
By analyzing requery events we have found that the cause of the
duplicate traffic is almost always a deficient name server, stub
resolver and/or application implementation combined with an
operational anomaly. The implementation deficiencies we have
identified to date include well-intentioned recovery attempts gone
awry, insufficient caching of failures, early abort when multiple
levels of glue records must be followed, and aggressive retry by stub
resolvers and/or applications. Anomalies that we have seen trigger
requery events include lame delegations, unusual glue records, and
anything that makes all authoritative name servers for a zone
unreachable (DoS attacks, crashes, maintenance, routing failures,
congestion, etc.).
In the following sections, we provide a detailed explanation of the
observed behavior and recommend changes that will reduce the requery
rate. Some of the changes recommended affect the core DNS protocol
specification, described principally in RFC 1034 [2], RFC 1035 [3]
and RFC 2181 [4].
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2. Observed name server misbehavior
2.1 Aggressive requerying for delegation information
There can be times when every name server in a zone's NS RRset is
unreachable (e.g., during a network outage), unavailable (e.g., the
name server process is not running on the server host) or
misconfigured (e.g., the name server is not authoritative for the
given zone, also known as "lame"). Consider a recursive name server
that attempts to resolve a query for a domain name in such a zone and
discovers that none of the zone's name servers can provide an answer.
We have observed a recursive name server implementation that then
verifies the zone's NS RRset in its cache by querying for the zone's
delegation information: it sends a query for the zone's NS RRset to
one of the parent zone's name servers.
For example, suppose that "example.com" has the following NS RRset:
example.com. IN NS ns1.example.com.
example.com. IN NS ns2.example.com.
Upon receipt of a query for "www.example.com" and assuming that
neither "ns1.example.com" nor "ns2.example.com" can provide an
answer, this recursive name server implementation immediately queries
a "com" zone name server for the "example.com" NS RRset to verify it
has the proper delegation information. This name server
implementation performs this query to a zone's parent zone for each
recursive query it receives that fails because of a completely
unresponsive set of name servers for the target zone. Consider the
effect when a popular zone experiences a catastrophic failure of all
its name servers: now every recursive query for domain names in that
zone sent to this name server implementation results in a query to
the failed zone's parent name servers. On one occasion when several
dozen popular zones became unreachable, the query load on the com/net
name servers increased by 50%.
We believe this verification query is not reasonable. Consider the
circumstances: When a recursive name server is resolving a query for
a domain name in a zone it has not previously searched, it uses the
list of name servers in the referral from the target zone's parent.
If on its first attempt to search the target zone, none of the name
servers in the referral is reachable, a verification query to the
parent is pointless: this query to the parent would come so quickly
on the heels of the referral that it would be almost certain to
contain the same list of name servers. The chance of discovering any
new information is slim.
The other possibility is that the recursive name server successfully
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contacts one of the target zone's name servers and then caches the NS
RRset from the authority section of a response, the proper behavior
according to section 5.4.1 of RFC 2181 [4], because the NS RRset from
the target zone is more trustworthy than delegation information from
the parent zone. If, while processing a subsequent recursive query,
the recursing name server discovers that none of the name servers
specified in the cached NS RRset is available or authoritative,
querying the parent would be wrong. An NS RRset from the parent zone
would now be less trustworthy than data already in the cache.
For this query of the parent zone to be useful, the target zone's
entire set of name servers would have to change AND the former set of
name servers would have to be deconfigured and/or decommissioned AND
the delegation information in the parent zone would have to be
updated with the new set of name servers, all within the TTL of the
target zone's NS RRset. We believe this scenario is uncommon:
administrative best practices dictate that changes to a zone's set of
name servers happen gradually, with servers that are removed from the
NS RRset left authoritative for the zone as long as possible. The
scenarios that we can envision that would benefit from the parent
requery behavior do not outweigh its damaging effects.
2.1.1 Recommendation
Name servers offering recursion MUST NOT send a query for the NS
RRset of a non-responsive zone to any of the name servers for that
zone's parent zone. For the purposes of this injunction, a
non-responsive zone is defined as a zone for which every name server
listed in the zone's NS RRset:
1. is not authoritative for the zone (i.e., lame), or,
2. returns a server failure response (RCODE=2), or,
3. is dead or unreachable according to section 7.2 of RFC 2308 [5].
2.2 Repeated queries to lame servers
Section 2.1 describes a catastrophic failure: when every name server
for a zone is unable to provide an answer for one reason or another.
A more common occurrence is a subset of a zone's name servers being
unavailable or misconfigured. Different failure modes have different
expected durations. Some symptoms indicate problems that are
potentially transient: various types of ICMP unreachable messages
because a name server process is not running or a host or network is
unreachable, or a complete lack of a response to a query. Such
responses could be the result of a host rebooting or temporary
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outages; these events don't necessarily require any human
intervention and can be reasonably expected to be temporary.
Other symptoms clearly indicate a condition requiring human
intervention, such as lame server: if a name server is misconfigured
and not authoritative for a zone delegated to it, it is reasonable to
assume that this condition has potential to last longer than
unreachability or unresponsiveness. Consequently, repeated queries
to known lame servers are not useful. In this case of a condition
with potential to persist for a long time, a better practice would be
to maintain a list of known lame servers and avoid querying them
repeatedly in a short interval.
2.2.1 Recommendation
Recursive name servers SHOULD cache name servers that they discover
are not authoritative for zones delegated to them (i.e. lame
servers). Lame servers MUST be cached against the specific query
tuple <zone name, class, server IP address>. Zone name can be
derived from the owner name of the NS record that was referenced to
query the name server that was discovered to be lame.
Implementations that perform lame server caching MUST refrain from
sending queries to known lame servers based on a time interval from
when the server is discovered to be lame. A minimum interval of
thirty minutes is RECOMMENDED.
2.3 Inability to follow multiple levels of out-of-zone glue
Some recursive name server implementations are unable to follow more
than one level of out-of-zone glue. For example, consider the
following delegations:
foo.example. IN NS ns1.example.com.
foo.example. IN NS ns2.example.com.
example.com. IN NS ns1.test.example.net.
example.com. IN NS ns2.test.example.net.
test.example.net. IN NS ns1.test.example.net.
test.example.net. IN NS ns2.test.example.net.
A name server processing a recursive query for "www.foo.example" must
follow two levels of indirection, first obtaining address records for
"ns1.test.example.net" and/or "ns2.test.example.net" in order to
obtain address records for "ns1.example.com" and/or "ns2.example.com"
in order to query those name servers for the address records of
"www.foo.example". While this situation may appear contrived, we
have seen multiple similar occurrences and expect more as new generic
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top-level domains (gTLDs) become active. We anticipate many zones in
the new gTLDs will use name servers in other gTLDs, increasing the
amount of inter-zone glue.
2.3.1 Recommendation
Clearly constructing a delegation that relies on multiple levels of
out-of-zone glue is not a good administrative practice. This issue
could be mitigated with an operational injunction in an RFC to
refrain from construction of such delegations. In our opinion the
practice is widespread enough to merit clarifications to the DNS
protocol specification to permit it on a limited basis.
Name servers offering recursion SHOULD be able to handle at least
three levels of indirection resulting from out-of-zone glue.
2.4 Aggressive retransmission when fetching glue
When an authoritative name server responds with a referral, it
includes NS records in the authority section of the response.
According to the algorithm in section 4.3.2 of RFC 1034 [2], the name
server should also "put whatever addresses are available into the
additional section, using glue RRs if the addresses are not available
from authoritative data or the cache." Some name server
implementations take this address inclusion a step further with a
feature called "glue fetching". A name server that implements glue
fetching attempts to include A records for every NS record in the
authority section. If necessary, the name server issues multiple
queries of its own to obtain any missing A records.
Problems with glue fetching can arise in the context of
"authoritative-only" name servers, which only serve authoritative
data and ignore requests for recursion. Such a server will not
generate any queries of its own. Instead it answers non-recursive
queries from resolvers looking for information in zones it serves.
With glue fetching enabled, however, an authoritative server will
generate queries whenever it needs to look up an unknown address
record to complete the additional section of a response.
We have observed situations where a glue-fetching name server can
send queries that reach other name servers, but apparently is
prevented from receiving the responses. For example, perhaps the
name server is authoritative-only and therefore its administrators
expect it to receive only queries. Perhaps unaware of glue fetching
and presuming that the name server will generate no queries, its
administrators place the name server behind a network device that
prevents it from receiving responses. If this is the case, all
glue-fetching queries will go answered.
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We have observed name server implementations that retry excessively
when glue-fetching queries are unanswered. A single com/net name
server has received hundreds of queries per second from a single name
server. Judging from the specific queries received and based on
additional analysis, we believe these queries result from overly
aggressive glue fetching.
2.4.1 Recommendation
Implementers whose name servers support glue fetching should take
care to avoid sending queries at excessive rates. Implementations
should support throttling logic to detect when queries are sent but
no responses are received.
2.5 Aggressive retransmission behind firewalls
A common occurrence and one of the largest sources of repeated
queries at the com/net and root name servers appears to result from
resolvers behind misconfigured firewalls. In this situation, a
recursive name server is apparently allowed to send queries through a
firewall to other name servers, but not receive the responses. The
result is more queries than necessary because of retransmission, all
of which are useless because the responses are never received. Just
as with the glue-fetching scenario described in Section 2.4, the
queries are sometimes sent at excessive rates. To make matters
worse, sometimes the responses, sent in reply to legitimate queries,
trigger an alarm on the originator's intrusion detection system. We
are frequently contacted by administrators responding to such alarms
who believe our name servers are attacking their systems.
Not only do some resolvers in this situation retransmit queries at an
excessive rate, but they continue to do so for days or even weeks.
This scenario could result from an organization with multiple
recursive name servers, only a subset of whose traffic is improperly
filtered in this manner. Stub resolvers in the organization could be
configured to query multiple name servers. Consider the case where a
stub resolver queries a filtered name server first. This name server
sends one or more queries whose replies are filtered, so it can't
respond to the stub resolver, which times out. The resolver
retransmits to a name server that is able to provide an answer.
Since resolution ultimately succeeds the underlying problem might not
be recognized or corrected. A popular stub resolver has a very
aggressive retransmission schedule, including simultaneous queries to
multiple name servers, which could explain how such a situation could
persist without being detected.
2.5.1 Recommendation
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The most obvious recommendation is that administrators should take
care not to place recursive name servers behind a firewall that
prohibits queries to pass through but not the resulting replies.
Name servers should take care to avoid sending queries at excessive
rates. Implementations should support throttling logic to detect
when queries are sent but no responses are received.
2.6 Misconfigured NS records
Sometimes a zone administrator forgets to add the trailing dot on the
domain names in the RDATA of a zone's NS records. Consider this
fragment of the zone file for "example.com":
$ORIGIN example.com.
example.com. 3600 IN NS ns1.example.com ; Note missing
example.com. 3600 IN NS ns2.example.com ; trailing dots
The zone's authoritative servers will parse the NS RDATA as
"ns1.example.com.example.com" and "ns2.example.com.example.com" and
return NS records with this incorrect RDATA in responses, including
typically the authority section of every response containing records
from the "example.com" zone.
Now consider a typical sequence of queries. A recursive name server
attempting to resolve A records for "www.example.com" with no cached
information for this zone will query a "com" authoritative server.
The "com" server responds with a referral to the "example.com" zone,
consisting of NS records with valid RDATA and associated glue
records. (This example assumes that the "example.com" zone
information is correct in the "com" zone.) The recursive name server
caches the NS RRset from the "com" server and follows the referral by
querying one of the "example.com" authoritative servers. This server
responds with the "www.example.com" A record in the answer section
and, typically, the "example.com" NS records in the authority section
and, if space in the message remains, glue A records in the
additional section. According to Section 5.4 of RFC 2181 [4], NS
records in the authority section of an authoritative answer are more
trustworthy than NS records from the authority section of a
non-authoritative answer. Thus the "example.com" NS RRset just
received from the "example.com" authoritative server displaces the
"example.com" NS RRset received moments ago from the "com"
authoritative server.
But the "example.com" zone contains the erroneous NS RRset as shown
in the example above. Subsequent queries for names in "example.com"
will cause the server to attempt to use the incorrect NS records and
so the server will try to resolve the nonexistent names
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"ns1.example.com.example.com" and "ns2.example.com.example.com". In
this example, since all of the zone's name servers are named in the
zone itself (i.e., "ns1.example.com.example.com" and
"ns2.example.com.example.com" both end in "example.com") and all are
bogus, the recursive server cannot reach any "example.com" name
servers. Therefore attempts to resolve these names result in A
record queries to the "com' authoritative servers. Queries for such
obviously bogus glue A records occur frequently at the com/net name
servers.
2.6.1 Recommendation
An authoritative server can detect this situation. A trailing dot
missing from an NS record's RDATA always results by definition in a
name server name that is in the zone. But any in-zone name server
should have a corresponding glue A record also in the zone. An
authoritative name server should report an error when a zone's NS
record references an in-zone name server without a corresponding glue
A record.
2.7 Name server records with zero TTL
Sometimes a popular com/net subdomain's zone is configured with a TTL
of zero on the zone's NS records, which prohibits these records from
being cached and will result in a higher query volume to the zone's
authoritative servers. The zone's administrator should understand
the consequences of such a configuration and provision resources
accordingly. A zero TTL on the zone's NS RRset, however, carries
additional consequences beyond the zone itself: if a recursive name
server cannot cache a zone's NS records because of a zero TTL, it
will be forced to query that zone's parent's name servers each time
it resolves a name in the zone. The com/net authoritative servers do
see an increased query load when a popular com/net subdomain's zone
is configured with a TTL of zero on the zone's NS records.
A zero TTL on an RRset expected to change frequently is extreme but
permissible. A zone's NS RRset is a special case, however, because
changes to it must be coordinated with the zone's parent. In most
zone parent/child relationships we are aware of, there is typically
some delay involved in effecting changes. Further, changes to the
set of a zone's authoritative name servers (and therefore to the
zone's NS RRset) are typically relatively rare: providing reliable
authoritative service requires a reasonably stable set of servers.
Therefore an extremely low or zero TTL on a zone's NS RRset rarely
makes sense, except in anticipation of an upcoming change. In this
case, when the zone's administrator has planned a change and does not
want recursive name servers throughout the Internet to cache the NS
RRset for a long period of time, a low TTL is reasonable.
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2.7.1 Recommendation
Because of the additional load placed on a zone's parent's
authoritative servers imposed by a zero TTL on a zone's NS RRset,
under such circumstances authoritative name servers should issue a
warning when loading a zone or refuse to load the zone altogether.
2.8 Unnecessary dynamic update messages
The UPDATE message specified in RFC 2136 [6] allows an authorized
agent to update a zone's data on an authoritative name server using a
DNS message sent over the network. Consider the case of an agent
desiring to add a particular resource record. Because of zone cuts,
the agent does not necessarily know the proper zone to which the
record should be added. The dynamic update process requires that the
agent determine the appropriate zone so the UPDATE message can be
sent to one of the zone's authoritative servers (typically the
primary master as specified in the zone's SOA MNAME field).
The appropriate zone to update is the closest enclosing zone, which
is the lowest zone in the name space. The closest enclosing zone
cannot be determined only by inspecting the domain name of the record
to be updated, since zone cuts can occur anywhere. One way to
determine the closest enclosing zone involves working up the name
space tree and sending repeated UPDATE messages until success. For
example, consider an agent attempting to add an A record with the
name "foo.bar.example.com". The agent could first attempt to update
the "foo.bar.example.com" zone. If the attempt failed, the update
could be directed to the "bar.example.com" zone, then the
"example.com" zone, then the "com" zone, and finally the root zone.
A popular dynamic agent follows this algorithm. The result is many
UPDATE messages received by the root name servers, the com/net
authoritative servers, and presumably other TLD authoritative
servers. A reasonable question is why the algorithm proceeds with
sending updates all the way to TLD and root name servers. In
enterprise DNS architectures with an "internal root" design, there
could conceivably be private, non-public TLD or root zones that would
be the appropriate target for a dynamic update. However, we question
if designing an algorithm to accommodate these limited cases is worth
the load it places on the public DNS in the form of unnecessary
UPDATE messages.
2.8.1 Recommendation
Dynamic update agents should not attempt to send UPDATE messages to
authoritative servers for TLD zones or the root zone by default. If
this functionality is supported, it should be require specific action
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by a user to be enabled.
2.9 Queries for domain names resembling IP addresses
The root name servers receive a significant number of A record
queries where the qname is an IP address. The source of these
queries is unknown. It could be attributed to situations where a
user believes an application will accept either a domain name or an
IP address in a given configuration option. The user enters an IP
address, but the application assumes any input is a domain name and
attempts to resolve it, resulting in an A record lookup. There could
also be applications that produce such queries in a misguided attempt
to reverse map IP addresses.
These queries result in Name Error (RCODE=3) responses. A recursive
name server can negatively cache such responses, but each response
requires a separate cache entry, i.e., a negative cache entry for the
domain name "192.0.2.1" does not prevent a subsequent query for the
domain name "192.0.2.2".
2.9.1 Recommendation
It would be desirable for the root name servers not to have to answer
these queries: they unnecessarily consume CPU resources and network
bandwidth. One possibility is for recursive name server
implementations to produce the Name Error response directly. We
suggest that implementors consider the option of synthesizing Name
Error responses at the recursive name server. The server could claim
authority for synthesized TLD zones corresponding to the first octet
of every possible IP address, e.g. 1., 2., through 255. This
behavior could be configurable in the (probably unlikely) event that
numeric TLDs are ever put into use.
Another option is to delegate these numeric TLDs from the root zone
to a separate set of servers to absorb the traffic. The "blackhole
servers" used by the the AS 112 Project [8], which are currently
delegated the in-addr.arpa zones corresponding to RFC 1918 [7]
private use address space, would be a possible choice to receive
these delegations.
2.10 Misdirected recursive queries
The root name servers receive a significant number of recursive
queries (i.e., queries with the RD bit set in the header). Since
none of the root servers offer recursion, the servers' response in
such a situation ignores the request for recursion and the response
probably does not contain the data the querier anticipated. Some of
these queries result from users configuring stub resolvers to query a
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root server. (This situation is not hypothetical: we have received
complaints from users when this configuration does not work as
hoped.) Of course, users should not direct stub resolvers to use name
servers that do not offer recursion, but we are not aware of any stub
resolver implementation that offers any feedback to the user when so
configured, aside from simply "not working".
2.10.1 Recommendation
When the IP address of a (supposedly) recursive name server is
configured in a stub resolver using an interactive user interface,
the resolver could send a test query to verify that the server
supports recursion (i.e., the response has the RA bit set in the
header). The user could be immediately notified if the server is
non-recursive.
The stub resolver could also report an error, either through a user
interface or in a log file, if the queried server does not support
recursion. Error reporting should be throttled to avoid a
notification or log message for every response from a non-recursive
server.
2.11 Suboptimal name server selection algorithm
An entire document could be devoted to the topic of problems with
different implementations of the recursive resolution algorithm. The
entire process of recursion is woefully underspecified, requiring
each implementor to design an algorithm. Sometimes implementors make
poor design choices that could be avoided if a suggested algorithm
and best practices were documented, but that is a topic for another
document.
Some deficiencies cause significant operational impact and are
therefore worth mentioning here. One of these is name server
selection by a recursive name server. When a recursive name server
wants to contact one of a zone's authoritative name servers, how does
it choose from the NS records listed in the zone's NS RRset? If the
selection mechanism is suboptimal, queries are not spread evenly
among a zone's authoritative servers. The details of the selection
mechanism are up to the implementor, but we offer some suggestions.
2.11.1 Recommendation
This list is not conclusive, but reflects the changes that would
produce the most impact in terms of reducing disproportionate query
load among a zone's authoritative servers. I.e., these changes would
help spread the query load evenly.
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o Do not make assumptions based on NS RRset order: all NS RRs should
be treated equally. (In the case of the "com" zone, for example,
most of the root servers return the NS record for
"a.gtld-servers.net" first in the authority section of referrals.
As a result, this server receives disproportionately more traffic
than the other 12 authoritative servers for "com".)
o Use all NS records in an RRset. (For example, we are aware of
implementations that hard-coded information for a subset of the
root servers.)
o Maintain state and favor the best-performing of a zone's
authoritative servers. A good definition of performance is
response time. Non-responsive servers can be penalized with an
extremely high response time.
o Do not lock onto the best-performing of a zone's name servers. A
recursive name server should periodically check the performance of
all of a zone's name servers to adjust its determination of the
best-performing one.
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3. IANA considerations
There are no new IANA considerations introduced by this
Internet-Draft.
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4. Security considerations
Name server and resolver misbehaviors identical or similar to those
discussed in this document expose the root and TLD name servers to
increased risk of both intentional and unintentional denial of
service.
We believe that implementation of the recommendations offered in this
document will reduce the amount of unnecessary traffic seen at root
and TLD name servers, thus reducing the opportunity for an attacker
to use such queries to his or her advantage.
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5. Internationalization considerations
We do not believe this document introduces any new
internationalization considerations to the DNS protocol
specification.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
[3] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[4] Elz, R. and R. Bush, "Clarifications to the DNS Specification",
RFC 2181, July 1997.
[5] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC
2308, March 1998.
[6] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April
1997.
[7] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E.
Lear, "Address Allocation for Private Internets", BCP 5, RFC
1918, February 1996.
[8] <http://www.as112.net>
Authors' Addresses
Matt Larson
VeriSign, Inc.
21345 Ridgetop Circle
Dulles, VA 20166-6503
USA
EMail: mlarson@verisign.com
Piet Barber
VeriSign, Inc.
21345 Ridgetop Circle
Dulles, VA 20166-6503
USA
EMail: pbarber@verisign.com
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