draft-ietf-dnsop-bad-dns-res-03.txt   draft-ietf-dnsop-bad-dns-res-04.txt 
DNS Operations M. Larson DNS Operations M. Larson
Internet-Draft P. Barber Internet-Draft P. Barber
Expires: April 27, 2005 VeriSign Expires: January 18, 2006 VeriSign
October 27, 2004 July 17, 2005
Observed DNS Resolution Misbehavior Observed DNS Resolution Misbehavior
draft-ietf-dnsop-bad-dns-res-03 draft-ietf-dnsop-bad-dns-res-04
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2005).
Abstract Abstract
This memo describes DNS name server and resolver behavior that This memo describes DNS iterative resolver behavior that results in a
results in a significant query volume sent to the root and top-level significant query volume sent to the root and top-level domain (TLD)
domain (TLD) name servers. In some cases we recommend minor name servers. We offer implementation advice to iterative resolver
additions to the DNS protocol specification and corresponding changes developers to alleviate these unnecessary queries. The
in iterative resolver implementations to alleviate these unnecessary recommendations made in this document are a direct byproduct of
queries. The recommendations made in this document are a direct observation and analysis of abnormal query traffic patterns seen at
byproduct of observation and analysis of abnormal query traffic two of the thirteen root name servers and all thirteen com/net TLD
patterns seen at two of the thirteen root name servers and all name servers.
thirteen com/net TLD name servers.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 A note about terminology in this memo . . . . . . . . . . 3 1.1 A note about terminology in this memo . . . . . . . . . . 3
2. Observed iterative resolver misbehavior . . . . . . . . . . 5 2. Observed iterative resolver misbehavior . . . . . . . . . . 5
2.1 Aggressive requerying for delegation information . . . . . 5 2.1 Aggressive requerying for delegation information . . . . . 5
2.1.1 Recommendation . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Recommendation . . . . . . . . . . . . . . . . . . . . 6
2.2 Repeated queries to lame servers . . . . . . . . . . . . . 6 2.2 Repeated queries to lame servers . . . . . . . . . . . . . 7
2.2.1 Recommendation . . . . . . . . . . . . . . . . . . . . 7 2.2.1 Recommendation . . . . . . . . . . . . . . . . . . . . 7
2.3 Inability to follow multiple levels of out-of-zone glue . 7 2.3 Inability to follow multiple levels of indirection . . . . 8
2.3.1 Recommendation . . . . . . . . . . . . . . . . . . . . 8 2.3.1 Recommendation . . . . . . . . . . . . . . . . . . . . 9
2.4 Aggressive retransmission when fetching glue . . . . . . . 8 2.4 Aggressive retransmission when fetching glue . . . . . . . 9
2.4.1 Recommendation . . . . . . . . . . . . . . . . . . . . 9 2.4.1 Recommendation . . . . . . . . . . . . . . . . . . . . 10
2.5 Aggressive retransmission behind firewalls . . . . . . . . 9 2.5 Aggressive retransmission behind firewalls . . . . . . . . 10
2.5.1 Recommendation . . . . . . . . . . . . . . . . . . . . 10 2.5.1 Recommendation . . . . . . . . . . . . . . . . . . . . 11
2.6 Misconfigured NS records . . . . . . . . . . . . . . . . . 10 2.6 Misconfigured NS records . . . . . . . . . . . . . . . . . 11
2.6.1 Recommendation . . . . . . . . . . . . . . . . . . . . 11 2.6.1 Recommendation . . . . . . . . . . . . . . . . . . . . 12
2.7 Name server records with zero TTL . . . . . . . . . . . . 11 2.7 Name server records with zero TTL . . . . . . . . . . . . 12
2.7.1 Recommendation . . . . . . . . . . . . . . . . . . . . 12 2.7.1 Recommendation . . . . . . . . . . . . . . . . . . . . 13
2.8 Unnecessary dynamic update messages . . . . . . . . . . . 12 2.8 Unnecessary dynamic update messages . . . . . . . . . . . 13
2.8.1 Recommendation . . . . . . . . . . . . . . . . . . . . 13 2.8.1 Recommendation . . . . . . . . . . . . . . . . . . . . 14
2.9 Queries for domain names resembling IP addresses . . . . . 13 2.9 Queries for domain names resembling IPv4 addresses . . . . 14
2.9.1 Recommendation . . . . . . . . . . . . . . . . . . . . 13 2.9.1 Recommendation . . . . . . . . . . . . . . . . . . . . 14
2.10 Misdirected recursive queries . . . . . . . . . . . . . 14 2.10 Misdirected recursive queries . . . . . . . . . . . . . 15
2.10.1 Recommendation . . . . . . . . . . . . . . . . . . . 14 2.10.1 Recommendation . . . . . . . . . . . . . . . . . . . 15
2.11 Suboptimal name server selection algorithm . . . . . . . 14 2.11 Suboptimal name server selection algorithm . . . . . . . 15
2.11.1 Recommendation . . . . . . . . . . . . . . . . . . . 15 2.11.1 Recommendation . . . . . . . . . . . . . . . . . . . 16
3. IANA considerations . . . . . . . . . . . . . . . . . . . . 16 3. IANA considerations . . . . . . . . . . . . . . . . . . . . 17
4. Security considerations . . . . . . . . . . . . . . . . . . 17 4. Security considerations . . . . . . . . . . . . . . . . . . 18
5. Internationalization considerations . . . . . . . . . . . . 18 5. Internationalization considerations . . . . . . . . . . . . 19
6. Normative References . . . . . . . . . . . . . . . . . . . . 18 6. Informative References . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . 20 Intellectual Property and Copyright Statements . . . . . . . 21
1. Introduction 1. Introduction
Observation of query traffic received by two root name servers and Observation of query traffic received by two root name servers and
the thirteen com/net TLD name servers has revealed that a large the thirteen com/net TLD name servers has revealed that a large
proportion of the total traffic often consists of "requeries". A proportion of the total traffic often consists of "requeries". A
requery is the same question (<qname, qtype, qclass>) asked requery is the same question (<QNAME, QTYPE, QCLASS>) asked
repeatedly at an unexpectedly high rate. We have observed requeries repeatedly at an unexpectedly high rate. We have observed requeries
from both a single IP address and multiple IP addresses (i.e., the from both a single IP address and multiple IP addresses (i.e., the
same query received simultaneously from multiple IP addresses). same query received simultaneously from multiple IP addresses).
By analyzing requery events we have found that the cause of the By analyzing requery events we have found that the cause of the
duplicate traffic is almost always a deficient iterative resolver, duplicate traffic is almost always a deficient iterative resolver,
stub resolver or application implementation combined with an stub resolver or application implementation combined with an
operational anomaly. The implementation deficiencies we have operational anomaly. The implementation deficiencies we have
identified to date include well-intentioned recovery attempts gone identified to date include well-intentioned recovery attempts gone
awry, insufficient caching of failures, early abort when multiple awry, insufficient caching of failures, early abort when multiple
levels of glue records must be followed, and aggressive retry by stub levels of indirection must be followed, and aggressive retry by stub
resolvers or applications. Anomalies that we have seen trigger resolvers or applications. Anomalies that we have seen trigger
requery events include lame delegations, unusual glue records, and requery events include lame delegations, unusual glue records, and
anything that makes all authoritative name servers for a zone anything that makes all authoritative name servers for a zone
unreachable (DoS attacks, crashes, maintenance, routing failures, unreachable (DoS attacks, crashes, maintenance, routing failures,
congestion, etc.). congestion, etc.).
In the following sections, we provide a detailed explanation of the In the following sections, we provide a detailed explanation of the
observed behavior and recommend changes that will reduce the requery observed behavior and recommend changes that will reduce the requery
rate. Some of the changes recommended affect the core DNS protocol rate. None of the changes recommended affects the core DNS protocol
specification, described principally in RFC 1034 [2], RFC 1035 [3] specification; instead, this document consists of guidelines to
and RFC 2181 [4]. implementors of iterative resolvers.
1.1 A note about terminology in this memo 1.1 A note about terminology in this memo
To recast an old saying about standards, the nice thing about DNS To recast an old saying about standards, the nice thing about DNS
terms is that there are so many of them to choose from. Writing or terms is that there are so many of them to choose from. Writing or
talking about DNS can be difficult and cause confusion resulting from talking about DNS can be difficult and cause confusion resulting from
a lack of agreed-upon terms for its various components. Further a lack of agreed-upon terms for its various components. Further
complicating matters are implementations that combine multiple roles complicating matters are implementations that combine multiple roles
into one piece of software, which makes naming the result into one piece of software, which makes naming the result
problematic. An example is the entity that accepts recursive problematic. An example is the entity that accepts recursive
queries, issues iterative queries as necessary to resolve the initial queries, issues iterative queries as necessary to resolve the initial
recursive query, caches responses it receives, and which is also able recursive query, caches responses it receives, and which is also able
answer questions about certain zones authoritatively. Often called a to answer questions about certain zones authoritatively. This entity
"recursive name server" or a "caching name server", it is in fact an is an iterative resolver combined with an authoritative name server
iterative resolver combined with an authoritative name server. and is often called a "recursive name server" or a "caching name
server".
This memo is concerned principally with the behavior of iterative This memo is concerned principally with the behavior of iterative
resolvers, which are typically found as part of a recursive name resolvers, which are typically found as part of a recursive name
server. This memo uses the more precise term "iterative resolver", server. This memo uses the more precise term "iterative resolver",
because the focus is usually on that component. In instances where because the focus is usually on that component. In instances where
the name server role of this entity requires mentioning, this memo the name server role of this entity requires mentioning, this memo
uses the term "recursive name server". For example, the name server uses the term "recursive name server". As an example of the
component of a recursive name server receives DNS queries and the difference, the name server component of a recursive name server
iterative resolver component sends queries. receives DNS queries and the iterative resolver component sends
queries.
The advent of IPv6 requires mentioning AAAA records as well as A The advent of IPv6 requires mentioning AAAA records as well as A
records when discussing glue. To avoid continuous repetition and records when discussing glue. To avoid continuous repetition and
qualification, this memo uses the general term "address records" to qualification, this memo uses the general term "address record" to
encompass both A and AAAA records when a particular situation is encompass both A and AAAA records when a particular situation is
relevant to both types. relevant to both types.
2. Observed iterative resolver misbehavior 2. Observed iterative resolver misbehavior
2.1 Aggressive requerying for delegation information 2.1 Aggressive requerying for delegation information
There can be times when every name server in a zone's NS RRset is 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 unreachable (e.g., during a network outage), unavailable (e.g., the
name server process is not running on the server host) or name server process is not running on the server host) or
misconfigured (e.g., the name server is not authoritative for the misconfigured (e.g., the name server is not authoritative for the
given zone, also known as "lame"). Consider an iterative resolver given zone, also known as "lame"). Consider an iterative resolver
that attempts to resolve a query for a domain name in such a zone and 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. discovers that none of the zone's name servers can provide an answer.
We have observed a recursive name server implementation whose We have observed a recursive name server implementation whose
iterative resolver then verifies the zone's NS RRset in its cache by iterative resolver then verifies the zone's NS RRset in its cache by
querying for the zone's delegation information: it sends a query for 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. the zone's NS RRset to one of the parent zone's name servers. (Note
that queries with QTYPE=NS are not required by the standard
resolution algorithm described in section 4.3.2 of RFC 1034 [2].
These NS queries represent this implementation's addition to that
algorithm.)
For example, suppose that "example.com" has the following NS RRset: For example, suppose that "example.com" has the following NS RRset:
example.com. IN NS ns1.example.com. example.com. IN NS ns1.example.com.
example.com. IN NS ns2.example.com. example.com. IN NS ns2.example.com.
Upon receipt of a query for "www.example.com" and assuming that Upon receipt of a query for "www.example.com" and assuming that
neither "ns1.example.com" nor "ns2.example.com" can provide an neither "ns1.example.com" nor "ns2.example.com" can provide an
answer, this iterative resolver implementation immediately queries a answer, this iterative resolver implementation immediately queries a
"com" zone name server for the "example.com" NS RRset to verify it "com" zone name server for the "example.com" NS RRset to verify it
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parent name servers. On one occasion when several dozen popular parent name servers. On one occasion when several dozen popular
zones became unreachable, the query load on the com/net name servers zones became unreachable, the query load on the com/net name servers
increased by 50%. increased by 50%.
We believe this verification query is not reasonable. Consider the We believe this verification query is not reasonable. Consider the
circumstances: When an iterative resolver is resolving a query for a circumstances: When an iterative resolver is resolving a query for a
domain name in a zone it has not previously searched, it uses the 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. 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 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 servers in the referral is reachable, a verification query to the
parent is pointless: this query to the parent would come so quickly parent would be pointless: this query to the parent would come so
on the heels of the referral that it would be almost certain to quickly on the heels of the referral that it would be almost certain
contain the same list of name servers. The chance of discovering any to contain the same list of name servers. The chance of discovering
new information is slim. any new information is slim.
The other possibility is that the iterative resolver successfully The other possibility is that the iterative resolver successfully
contacts one of the target zone's name servers and then caches the NS 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 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 according to section 5.4.1 of RFC 2181 [3], because the NS RRset from
the target zone is more trustworthy than delegation information from the target zone is more trustworthy than delegation information from
the parent zone. If, while processing a subsequent recursive query, the parent zone. If, while processing a subsequent recursive query,
the iterative resolver discovers that none of the name servers the iterative resolver discovers that none of the name servers
specified in the cached NS RRset is available or authoritative, specified in the cached NS RRset is available or authoritative,
querying the parent would be wrong. An NS RRset from the parent zone querying the parent would be wrong. An NS RRset from the parent zone
would now be less trustworthy than data already in the cache. 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 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 entire set of name servers would have to change AND the former set of
name servers would have to be deconfigured or decommissioned AND the name servers would have to be deconfigured or decommissioned AND the
delegation information in the parent zone would have to be updated 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 with the new set of name servers, all within the TTL of the target
zone's NS RRset. We believe this scenario is uncommon: zone's NS RRset. We believe this scenario is uncommon:
administrative best practices dictate that changes to a zone's set of administrative best practices dictate that changes to a zone's set of
name servers happen gradually when at all possible, with servers name servers happen gradually when at all possible, with servers
removed from the NS RRset left authoritative for the zone as long as removed from the NS RRset left authoritative for the zone as long as
possible. The scenarios that we can envision that would benefit from possible. The scenarios that we can envision that would benefit from
the parent requery behavior do not outweigh its damaging effects. the parent requery behavior do not outweigh its damaging effects.
This section should not be understood to claim that all queries to a
zone's parent are bad. In some cases, such queries are not only
reasonable but required. Consider the situation when required
information, such as the address of a name server (i.e., the address
record corresponding to the RDATA of an NS record), has timed out of
an iterative resolver's cache before the corresponding NS record. If
the name of the name server is below the apex of the zone, then the
name server's address record is only available as glue in the parent
zone. For example, consider this NS record:
example.com. IN NS ns.example.com.
If a cache has this NS record but not the address record for
"ns.example.com", it is unable to contact the "example.com" zone
directly and must query the "com" zone to obtain the address record.
Note, however, that such a query would not have QTYPE=NS according to
the standard resolution algorithm.
2.1.1 Recommendation 2.1.1 Recommendation
An iterative resolver MUST NOT send a query for the NS RRset of a An iterative resolver 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 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 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 defined as a zone for which every name server listed in the zone's NS
RRset: RRset:
1. is not authoritative for the zone (i.e., lame), or, 1. is not authoritative for the zone (i.e., lame), or,
2. returns a server failure response (RCODE=2), or, 2. returns a server failure response (RCODE=2), or,
3. is dead or unreachable according to section 7.2 of RFC 2308 [5].
3. is dead or unreachable according to section 7.2 of RFC 2308 [4].
2.2 Repeated queries to lame servers 2.2 Repeated queries to lame servers
Section 2.1 describes a catastrophic failure: when every name server 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. for a zone is unable to provide an answer for one reason or another.
A more common occurrence is when a subset of a zone's name servers A more common occurrence is when a subset of a zone's name servers
are unavailable or misconfigured. Different failure modes have are unavailable or misconfigured. Different failure modes have
different expected durations. Some symptoms indicate problems that different expected durations. Some symptoms indicate problems that
are potentially transient; for example, various types of ICMP are potentially transient; for example, various types of ICMP
unreachable messages because a name server process is not running or unreachable messages because a name server process is not running or
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Other symptoms clearly indicate a condition requiring human Other symptoms clearly indicate a condition requiring human
intervention, such as lame server: if a name server is misconfigured intervention, such as lame server: if a name server is misconfigured
and not authoritative for a zone delegated to it, it is reasonable to and not authoritative for a zone delegated to it, it is reasonable to
assume that this condition has potential to last longer than assume that this condition has potential to last longer than
unreachability or unresponsiveness. Consequently, repeated queries unreachability or unresponsiveness. Consequently, repeated queries
to known lame servers are not useful. In this case of a condition 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 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 to maintain a list of known lame servers and avoid querying them
repeatedly in a short interval. repeatedly in a short interval.
It should also be noted, however, that some authoritative name server
implementations appear to be lame only for queries of certain types
as described in RFC 4074 [5]. In this case, it makes sense to retry
the "lame" servers for other types of queries, particularly when all
known authoritative name servers appear to be "lame".
2.2.1 Recommendation 2.2.1 Recommendation
Iterative resolvers SHOULD cache name servers that they discover are Iterative resolvers SHOULD cache name servers that they discover are
not authoritative for zones delegated to them (i.e. lame servers). not authoritative for zones delegated to them (i.e. lame servers).
Lame servers MUST be cached against the specific query tuple <zone If this caching is performed, lame servers MUST be cached against the
name, class, server IP address>. Zone name can be derived from the specific query tuple <zone name, class, server IP address>. Zone
owner name of the NS record that was referenced to query the name name can be derived from the owner name of the NS record that was
server that was discovered to be lame. Implementations that perform referenced to query the name server that was discovered to be lame.
lame server caching MUST refrain from sending queries to known lame Implementations that perform lame server caching MUST refrain from
servers based on a time interval from when the server is discovered sending queries to known lame servers based on a time interval from
to be lame. A minimum interval of thirty minutes is RECOMMENDED. 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 An exception to this recommendation occurs if all name servers for a
zone are marked lame. In that case, the iterative resolver SHOULD
temporarily ignore the servers' lameness status and query one or more
servers. This behavior is a workaround for the type-specific
lameness issue described in the previous section.
Some iterative resolver implementations are unable to follow more Implementors should take care not to make lame server avoidance logic
than one level of out-of-zone glue. For example, consider the overly broad: note that a name server could be lame for a parent zone
but not a child zone, e.g., lame for "example.com" but properly
authoritative for "sub.example.com". Therefore a name server should
not be automatically considered lame for subzones. In the case
above, even if a name server is known to be lame for "example.com",
it should be queried for QNAMEs at or below "sub.example.com" if an
NS record indicates it should be authoritative for that zone.
2.3 Inability to follow multiple levels of indirection
Some iterative resolver implementations are unable to follow
sufficient levels of indirection. For example, consider the
following delegations: following delegations:
foo.example. IN NS ns1.example.com. foo.example. IN NS ns1.example.com.
foo.example. IN NS ns2.example.com. foo.example. IN NS ns2.example.com.
example.com. IN NS ns1.test.example.net. example.com. IN NS ns1.test.example.net.
example.com. IN NS ns2.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 ns1.test.example.net.
test.example.net. IN NS ns2.test.example.net. test.example.net. IN NS ns2.test.example.net.
An iterative resolver resolving the name "www.foo.example" must An iterative resolver resolving the name "www.foo.example" must
follow two levels of indirection, first obtaining address records for follow two levels of indirection, first obtaining address records for
"ns1.test.example.net" or "ns2.test.example.net" in order to obtain "ns1.test.example.net" or "ns2.test.example.net" in order to obtain
address records for "ns1.example.com" or "ns2.example.com" in order address records for "ns1.example.com" or "ns2.example.com" in order
to query those name servers for the address records of to query those name servers for the address records of
"www.foo.example". While this situation may appear contrived, we "www.foo.example". While this situation may appear contrived, we
have seen multiple similar occurrences and expect more as new generic have seen multiple similar occurrences and expect more as new generic
top-level domains (gTLDs) become active. We anticipate many zones in top-level domains (gTLDs) become active. We anticipate many zones in
new gTLDs will use name servers in other gTLDs, increasing the amount new gTLDs will use name servers in existing gTLDs, increasing the
of inter-zone glue. number of delegations using out-of-zone name servers.
2.3.1 Recommendation 2.3.1 Recommendation
Clearly constructing a delegation that relies on multiple levels of Clearly constructing a delegation that relies on multiple levels of
out-of-zone glue is not a good administrative practice. This issue indirection is not a good administrative practice. However, the
could be mitigated with an operational injunction in an RFC to practice is widespread enough to require that iterative resolvers be
refrain from construction of such delegations. In our opinion the able to cope with it. Iterative resolvers SHOULD be able to handle
practice is widespread enough to merit clarifications to the DNS arbitrary levels of indirection resulting from out-of-zone name
protocol specification to permit it on a limited basis. servers. Iterative resolvers SHOULD implement a level-of-effort
counter to avoid loops or otherwise performing too much work in
resolving pathological cases.
Iterative resolvers SHOULD be able to handle at least three levels of A best practice that avoids this entire issue of indirection is to
indirection resulting from out-of-zone glue. name one or more of a zone's name servers in the zone itself. For
example, if the zone is named "example.com", consider naming some of
the name servers "ns{1,2,...}.example.com" (or similar).
2.4 Aggressive retransmission when fetching glue 2.4 Aggressive retransmission when fetching glue
When an authoritative name server responds with a referral, it When an authoritative name server responds with a referral, it
includes NS records in the authority section of the response. 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 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 server should also "put whatever addresses are available into the
additional section, using glue RRs if the addresses are not available additional section, using glue RRs if the addresses are not available
from authoritative data or the cache." Some name server from authoritative data or the cache." Some name server
implementations take this address inclusion a step further with a implementations take this address inclusion a step further with a
feature called "glue fetching". A name server that implements glue feature called "glue fetching". A name server that implements glue
fetching attempts to include address records for every NS record in fetching attempts to include address records for every NS record in
the authority section. If necessary, the name server issues multiple the authority section. If necessary, the name server issues multiple
queries of its own to obtain any missing address records. queries of its own to obtain any missing address records.
Problems with glue fetching can arise in the context of Problems with glue fetching can arise in the context of
"authoritative-only" name servers, which only serve authoritative "authoritative-only" name servers, which only serve authoritative
data and ignore requests for recursion. Such an entity will not data and ignore requests for recursion. Such an entity will not
normally generate any queries of its own. Instead it answers normally generate any queries of its own. Instead it answers non-
non-recursive queries from iterative resolvers looking for recursive queries from iterative resolvers looking for information in
information in zones it serves. With glue fetching enabled, however, zones it serves. With glue fetching enabled, however, an
an authoritative server invokes an iterative resolver to look up an authoritative server invokes an iterative resolver to look up an
unknown address record to complete the additional section of a unknown address record to complete the additional section of a
response. response.
We have observed situations where the iterative resolver of a We have observed situations where the iterative resolver of a glue-
glue-fetching name server can send queries that reach other name fetching name server can send queries that reach other name servers,
servers, but is apparently prevented from receiving the responses. but is apparently prevented from receiving the responses. For
For example, perhaps the name server is authoritative-only and example, perhaps the name server is authoritative-only and therefore
therefore its administrators expect it to receive only queries and its administrators expect it to receive only queries and not
not responses. Perhaps unaware of glue fetching and presuming that responses. Perhaps unaware of glue fetching and presuming that the
the name server's iterative resolver will generate no queries, its name server's iterative resolver will generate no queries, its
administrators place the name server behind a network device that administrators place the name server behind a network device that
prevents it from receiving responses. If this is the case, all prevents it from receiving responses. If this is the case, all glue-
glue-fetching queries will go answered. fetching queries will go answered.
We have observed name server implementations whose iterative We have observed name server implementations whose iterative
resolvers retry excessively when glue-fetching queries are resolvers retry excessively when glue-fetching queries are
unanswered. A single com/net name server has received hundreds of unanswered. A single com/net name server has received hundreds of
queries per second from a single such source. Judging from the queries per second from a single such source. Judging from the
specific queries received and based on additional analysis, we specific queries received and based on additional analysis, we
believe these queries result from overly aggressive glue fetching. believe these queries result from overly aggressive glue fetching.
2.4.1 Recommendation 2.4.1 Recommendation
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server. The "com" server responds with a referral to the server. The "com" server responds with a referral to the
"example.com" zone, consisting of NS records with valid RDATA and "example.com" zone, consisting of NS records with valid RDATA and
associated glue records. (This example assumes that the associated glue records. (This example assumes that the
"example.com" zone delegation information is correct in the "com" "example.com" zone delegation information is correct in the "com"
zone.) The iterative resolver caches the NS RRset from the "com" zone.) The iterative resolver caches the NS RRset from the "com"
server and follows the referral by querying one of the "example.com" server and follows the referral by querying one of the "example.com"
authoritative servers. This server responds with the authoritative servers. This server responds with the
"www.example.com" address record in the answer section and, "www.example.com" address record in the answer section and,
typically, the "example.com" NS records in the authority section and, typically, the "example.com" NS records in the authority section and,
if space in the message remains, glue address records in the if space in the message remains, glue address records in the
additional section. According to Section 5.4 of RFC 2181 [4], NS additional section. According to Section 5.4 of RFC 2181 [3], NS
records in the authority section of an authoritative answer are more records in the authority section of an authoritative answer are more
trustworthy than NS records from the authority section of a trustworthy than NS records from the authority section of a non-
non-authoritative answer. Thus the "example.com" NS RRset just authoritative answer. Thus the "example.com" NS RRset just received
received from the "example.com" authoritative server overrides the from the "example.com" authoritative server overrides the
"example.com" NS RRset received moments ago from the "com" "example.com" NS RRset received moments ago from the "com"
authoritative server. authoritative server.
But the "example.com" zone contains the erroneous NS RRset as shown But the "example.com" zone contains the erroneous NS RRset as shown
in the example above. Subsequent queries for names in "example.com" in the example above. Subsequent queries for names in "example.com"
will cause the iterative resolver to attempt to use the incorrect NS will cause the iterative resolver to attempt to use the incorrect NS
records and so it will try to resolve the nonexistent names records and so it will try to resolve the nonexistent names
"ns1.example.com.example.com" and "ns2.example.com.example.com". In "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 this example, since all of the zone's name servers are named in the
zone itself (i.e., "ns1.example.com.example.com" and zone itself (i.e., "ns1.example.com.example.com" and
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bogus, the iterative resolver cannot reach any "example.com" name bogus, the iterative resolver cannot reach any "example.com" name
servers. Therefore attempts to resolve these names result in address servers. Therefore attempts to resolve these names result in address
record queries to the "com" authoritative servers. Queries for such record queries to the "com" authoritative servers. Queries for such
obviously bogus glue address records occur frequently at the com/net obviously bogus glue address records occur frequently at the com/net
name servers. name servers.
2.6.1 Recommendation 2.6.1 Recommendation
An authoritative server can detect this situation. A trailing dot An authoritative server can detect this situation. A trailing dot
missing from an NS record's RDATA always results by definition in a missing from an NS record's RDATA always results by definition in a
name server name that exists somewhere under the SOA of the zone the name server name that exists somewhere under the apex of the zone the
NS record appears in. Note that further levels of delegation are NS record appears in. Note that further levels of delegation are
possible, so a missing trailing dot could inadvertently create a name possible, so a missing trailing dot could inadvertently create a name
server name that actually exists in a subzone. But in any case, the server name that actually exists in a subzone.
address record must still be present in this zone, either as
authoritative data or glue.
An authoritative name server SHOULD report an error when one of a An authoritative name server SHOULD issue a warning when one of a
zone's NS records references a name server below the zone's SOA when zone's NS records references a name server below the zone's apex when
a corresponding address record does not exist in the zone. a corresponding address record does not exist in the zone AND there
are no delegated subzones where the address record could exist.
2.7 Name server records with zero TTL 2.7 Name server records with zero TTL
Sometimes a popular com/net subdomain's zone is configured with a 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 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 being cached and will result in a higher query volume to the zone's
authoritative servers. The zone's administrator should understand authoritative servers. The zone's administrator should understand
the consequences of such a configuration and provision resources the consequences of such a configuration and provision resources
accordingly. A zero TTL on the zone's NS RRset, however, carries accordingly. A zero TTL on the zone's NS RRset, however, carries
additional consequences beyond the zone itself: if an iterative additional consequences beyond the zone itself: if an iterative
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makes sense, except in anticipation of an upcoming change. In this makes sense, except in anticipation of an upcoming change. In this
case, when the zone's administrator has planned a change and does not case, when the zone's administrator has planned a change and does not
want iterative resolvers throughout the Internet to cache the NS want iterative resolvers throughout the Internet to cache the NS
RRset for a long period of time, a low TTL is reasonable. RRset for a long period of time, a low TTL is reasonable.
2.7.1 Recommendation 2.7.1 Recommendation
Because of the additional load placed on a zone's parent's Because of the additional load placed on a zone's parent's
authoritative servers resulting from a zero TTL on a zone's NS RRset, authoritative servers resulting from a zero TTL on a zone's NS RRset,
under such circumstances authoritative name servers SHOULD issue a under such circumstances authoritative name servers SHOULD issue a
warning when loading a zone or refuse to load the zone altogether. warning when loading a zone.
2.8 Unnecessary dynamic update messages 2.8 Unnecessary dynamic update messages
The UPDATE message specified in RFC 2136 [6] allows an authorized 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 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 DNS message sent over the network. Consider the case of an agent
desiring to add a particular resource record. Because of zone cuts, desiring to add a particular resource record. Because of zone cuts,
the agent does not necessarily know the proper zone to which the the agent does not necessarily know the proper zone to which the
record should be added. The dynamic update process requires that the record should be added. The dynamic update process requires that the
agent determine the appropriate zone so the UPDATE message can be agent determine the appropriate zone so the UPDATE message can be
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update the "foo.bar.example.com" zone. If the attempt failed, the update the "foo.bar.example.com" zone. If the attempt failed, the
update could be directed to the "bar.example.com" zone, then 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. "example.com" zone, then the "com" zone, and finally the root zone.
A popular dynamic agent follows this algorithm. The result is many A popular dynamic agent follows this algorithm. The result is many
UPDATE messages received by the root name servers, the com/net UPDATE messages received by the root name servers, the com/net
authoritative servers, and presumably other TLD authoritative authoritative servers, and presumably other TLD authoritative
servers. A valid question is why the algorithm proceeds to send servers. A valid question is why the algorithm proceeds to send
updates all the way to TLD and root name servers. This behavior is updates all the way to TLD and root name servers. This behavior is
not entirely unreasonable: in enterprise DNS architectures with an not entirely unreasonable: in enterprise DNS architectures with an
"internal root" design, there could conceivably be private, "internal root" design, there could conceivably be private, non-
non-public TLD or root zones that would be the appropriate targets public TLD or root zones that would be the appropriate targets for a
for a dynamic update. dynamic update.
A significant deficiency with this algorithm is that knowledge of a A significant deficiency with this algorithm is that knowledge of a
given UPDATE message's failure is not helpful in directing future given UPDATE message's failure is not helpful in directing future
UPDATE messages to the appropriate servers. A better algorithm would UPDATE messages to the appropriate servers. A better algorithm would
be to find the closest enclosing zone by walking up the name space be to find the closest enclosing zone by walking up the name space
with queries for SOA or NS rather than "probing" with UPDATE with queries for SOA or NS rather than "probing" with UPDATE
messages. Once the appropriate zone is found, an UPDATE message can messages. Once the appropriate zone is found, an UPDATE message can
be sent. In addition, the results of these queries can be cached to be sent. In addition, the results of these queries can be cached to
aid in determining closest enclosing zones for future updates. Once aid in determining closest enclosing zones for future updates. Once
the closest enclosing zone is determined with this method, the update the closest enclosing zone is determined with this method, the update
will either succeed or fail and there is no need to send further will either succeed or fail and there is no need to send further
updates to higher-level zones. The important point is that walking updates to higher-level zones. The important point is that walking
up the tree with queries yields cacheable information, whereas up the tree with queries yields cacheable information, whereas
walking up the tree by sending UPDATE messages does not. walking up the tree by sending UPDATE messages does not.
2.8.1 Recommendation 2.8.1 Recommendation
Dynamic update agents SHOULD send SOA or NS queries to progressively Dynamic update agents SHOULD send SOA or NS queries to progressively
higher-level zones to find the closest enclosing zone for a given higher-level names to find the closest enclosing zone for a given
name to update. Only after the appropriate zone is found should the name to update. Only after the appropriate zone is found should the
client send an UPDATE message to one of the zone's authoritative client send an UPDATE message to one of the zone's authoritative
servers. Update clients SHOULD NOT "probe" using UPDATE messages by servers. Update clients SHOULD NOT "probe" using UPDATE messages by
walking up the tree to progressively higher-level zones. walking up the tree to progressively higher-level zones.
2.9 Queries for domain names resembling IP addresses 2.9 Queries for domain names resembling IPv4 addresses
The root name servers receive a significant number of A record The root name servers receive a significant number of A record
queries where the qname is an IP address. The source of these queries where the QNAME looks like an IPv4 address. The source of
queries is unknown. It could be attributed to situations where a these queries is unknown. It could be attributed to situations where
user believes an application will accept either a domain name or an 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 IP address in a given configuration option. The user enters an IP
address, but the application assumes any input is a domain name and address, but the application assumes any input is a domain name and
attempts to resolve it, resulting in an A record lookup. There could attempts to resolve it, resulting in an A record lookup. There could
also be applications that produce such queries in a misguided attempt also be applications that produce such queries in a misguided attempt
to reverse map IP addresses. to reverse map IP addresses.
These queries result in Name Error (RCODE=3) responses. An iterative These queries result in Name Error (RCODE=3) responses. An iterative
resolver can negatively cache such responses, but each response resolver can negatively cache such responses, but each response
requires a separate cache entry, i.e., a negative cache entry for the 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 "192.0.2.1" does not prevent a subsequent query for the
domain name "192.0.2.2". domain name "192.0.2.2".
2.9.1 Recommendation 2.9.1 Recommendation
It would be desirable for the root name servers not to have to answer It would be desirable for the root name servers not to have to answer
these queries: they unnecessarily consume CPU resources and network these queries: they unnecessarily consume CPU resources and network
bandwidth. One possibility is for iterative resolver implementations bandwidth. A possible solution is to delegate these numeric TLDs
to produce the Name Error response directly. We suggest that from the root zone to a separate set of servers to absorb the
implementors consider the option of synthesizing Name Error responses traffic. The "black hole servers" used by the AS 112 Project [8],
at the iterative resolver. The server could claim authority for which are currently delegated the in-addr.arpa zones corresponding to
synthesized TLD zones corresponding to the first octet of every RFC 1918 [7] private use address space, would be a possible choice to
possible IP address, e.g. 1., 2., through 255. This behavior could receive these delegations. Of course, the proper and usual root zone
be configurable in the (probably unlikely) event that numeric TLDs change procedures would have to be followed to make such a change to
are ever put into use. the root zone.
Another option is to delegate these numeric TLDs from the root zone
to a separate set of servers to absorb the traffic. The "black hole
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 2.10 Misdirected recursive queries
The root name servers receive a significant number of recursive The root name servers receive a significant number of recursive
queries (i.e., queries with the RD bit set in the header). Since queries (i.e., queries with the RD bit set in the header). Since
none of the root servers offers recursion, the servers' response in none of the root servers offers recursion, the servers' response in
such a situation ignores the request for recursion and the response such a situation ignores the request for recursion and the response
probably does not contain the data the querier anticipated. Some of probably does not contain the data the querier anticipated. Some of
these queries result from users configuring stub resolvers to query a these queries result from users configuring stub resolvers to query a
root server. (This situation is not hypothetical: we have received root server. (This situation is not hypothetical: we have received
complaints from users when this configuration does not work as complaints from users when this configuration does not work as
hoped.) Of course, users should not direct stub resolvers to use name hoped.) Of course, users should not direct stub resolvers to use
servers that do not offer recursion, but we are not aware of any stub name servers that do not offer recursion, but we are not aware of any
resolver implementation that offers any feedback to the user when so stub resolver implementation that offers any feedback to the user
configured, aside from simply "not working". when so configured, aside from simply "not working".
2.10.1 Recommendation 2.10.1 Recommendation
When the IP address of a name server that supposedly offers recursion When the IP address of a name server that supposedly offers recursion
is configured in a stub resolver using an interactive user interface, is configured in a stub resolver using an interactive user interface,
the resolver could send a test query to verify that the server indeed the resolver could send a test query to verify that the server indeed
supports recursion (i.e., verify that the response has the RA bit set supports recursion (i.e., verify that the response has the RA bit set
in the header). The user could be immediately notified if the server in the header). The user could be immediately notified if the server
is non-recursive. is non-recursive.
skipping to change at page 15, line 24 skipping to change at page 16, line 20
selection mechanism is suboptimal, queries are not spread evenly selection mechanism is suboptimal, queries are not spread evenly
among a zone's authoritative servers. The details of the selection among a zone's authoritative servers. The details of the selection
mechanism are up to the implementor, but we offer some suggestions. mechanism are up to the implementor, but we offer some suggestions.
2.11.1 Recommendation 2.11.1 Recommendation
This list is not conclusive, but reflects the changes that would This list is not conclusive, but reflects the changes that would
produce the most impact in terms of reducing disproportionate query produce the most impact in terms of reducing disproportionate query
load among a zone's authoritative servers. I.e., these changes would load among a zone's authoritative servers. I.e., these changes would
help spread the query load evenly. help spread the query load evenly.
o Do not make assumptions based on NS RRset order: all NS RRs SHOULD 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, be treated equally. (In the case of the "com" zone, for example,
most of the root servers return the NS record for most of the root servers return the NS record for "a.gtld-
"a.gtld-servers.net" first in the authority section of referrals. servers.net" first in the authority section of referrals.
Apparently as a result, this server receives disproportionately Apparently as a result, this server receives disproportionately
more traffic than the other 12 authoritative servers for "com".) more traffic than the other 12 authoritative servers for "com".)
o Use all NS records in an RRset. (For example, we are aware of o Use all NS records in an RRset. (For example, we are aware of
implementations that hard-coded information for a subset of the implementations that hard-coded information for a subset of the
root servers.) root servers.)
o Maintain state and favor the best-performing of a zone's o Maintain state and favor the best-performing of a zone's
authoritative servers. A good definition of performance is authoritative servers. A good definition of performance is
response time. Non-responsive servers can be penalized with an response time. Non-responsive servers can be penalized with an
extremely high response time. extremely high response time.
o Do not lock onto the best-performing of a zone's name servers. An o Do not lock onto the best-performing of a zone's name servers. An
iterative resolver SHOULD periodically check the performance of iterative resolver SHOULD periodically check the performance of
all of a zone's name servers to adjust its determination of the all of a zone's name servers to adjust its determination of the
best-performing one. best-performing one.
3. IANA considerations 3. IANA considerations
There are no new IANA considerations introduced by this memo. There are no new IANA considerations introduced by this memo.
4. Security considerations 4. Security considerations
skipping to change at page 17, line 7 skipping to change at page 18, line 7
iterative resolver SHOULD periodically check the performance of iterative resolver SHOULD periodically check the performance of
all of a zone's name servers to adjust its determination of the all of a zone's name servers to adjust its determination of the
best-performing one. best-performing one.
3. IANA considerations 3. IANA considerations
There are no new IANA considerations introduced by this memo. There are no new IANA considerations introduced by this memo.
4. Security considerations 4. Security considerations
Name server and resolver misbehaviors identical or similar to those The iterative resolver misbehavior discussed in this document exposes
discussed in this document expose the root and TLD name servers to the root and TLD name servers to increased risk of both intentional
increased risk of both intentional and unintentional denial of and unintentional denial of service attacks.
service.
We believe that implementation of the recommendations offered in this We believe that implementation of the recommendations offered in this
document will reduce the amount of unnecessary traffic seen at root document will reduce the amount of unnecessary traffic seen at root
and TLD name servers, thus reducing the opportunity for an attacker and TLD name servers, thus reducing the opportunity for an attacker
to use such queries to his or her advantage. to use such queries to his or her advantage.
5. Internationalization considerations 5. Internationalization considerations
We do not believe this document introduces any new There are no new internationalization considerations introduced by
internationalization considerations to the DNS protocol this memo.
specification.
6 Normative References 6. Informative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Mockapetris, P., "Domain names - concepts and facilities", STD [2] Mockapetris, P., "Domain names - concepts and facilities",
13, RFC 1034, November 1987. 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", [3] Elz, R. and R. Bush, "Clarifications to the DNS Specification",
RFC 2181, July 1997. RFC 2181, July 1997.
[5] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC [4] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)",
2308, March 1998. RFC 2308, March 1998.
[6] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic [5] Morishita, Y. and T. Jinmei, "Common Misbehavior Against DNS
Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April Queries for IPv6 Addresses", RFC 4074, May 2005.
1997.
[7] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. [6] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic
Lear, "Address Allocation for Private Internets", BCP 5, RFC Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
1918, February 1996. 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> [8] <http://www.as112.net>
Authors' Addresses Authors' Addresses
Matt Larson Matt Larson
VeriSign, Inc. VeriSign, Inc.
21345 Ridgetop Circle 21345 Ridgetop Circle
Dulles, VA 20166-6503 Dulles, VA 20166-6503
USA USA
EMail: mlarson@verisign.com Email: mlarson@verisign.com
Piet Barber Piet Barber
VeriSign, Inc. VeriSign, Inc.
21345 Ridgetop Circle 21345 Ridgetop Circle
Dulles, VA 20166-6503 Dulles, VA 20166-6503
USA USA
EMail: pbarber@verisign.com Email: pbarber@verisign.com
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
skipping to change at page 20, line 41 skipping to change at page 21, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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