draft-ietf-dnsop-respsize-08.txt   draft-ietf-dnsop-respsize-09.txt 
DNSOP Working Group Paul Vixie, ISC Internet Engineering Task Force P. Vixie
INTERNET-DRAFT Akira Kato, WIDE Internet-Draft Internet Systems Consortium
<draft-ietf-dnsop-respsize-08.txt> November 19, 2007 Intended status: Informational A. Kato
Expires: June 20, 2008 The University of Tokyo/WIDE
Project
December 18, 2007
DNS Referral Response Size Issues DNS Referral Response Size Issues
draft-ietf-dnsop-respsize-09
Status of this Memo Status of this Memo
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This Internet-Draft will expire on June 20, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
With a mandated default minimum maximum UDP message size of 512 With a mandated default minimum maximum UDP message size of 512
octets, the DNS protocol presents some special problems for zones octets, the DNS protocol presents some special problems for zones
wishing to expose a moderate or high number of authority servers (NS wishing to expose a moderate or high number of authority servers (NS
RRs). This document explains the operational issues caused by, or RRs). This document explains the operational issues caused by, or
related to this response size limit, and suggests ways to optimize related to this response size limit, and suggests ways to optimize
the use of this limited space. Guidance is offered to DNS server the use of this limited space. Guidance is offered to DNS server
implementors and to DNS zone operators. implementors and to DNS zone operators.
INTERNET-DRAFT November 19, 2007 RESPSIZE 1. Introduction
1 - Introduction and Overview 1.1. Introduction and Overview
1.1. The DNS standard (see [RFC1035 4.2.1]) limits message size to 512 The DNS standard limits UDP message size to 512 octets (see [RFC1035]
octets. Even though this limitation was due to the required minimum IP 4.2.1). Even though this limitation was due to the required minimum
reassembly limit for IPv4, it became a hard DNS protocol limit and is IP reassembly limit for IPv4, it became a hard DNS protocol limit and
not implicitly relaxed by changes in a network layer protocol, for is not implicitly relaxed by changes in a network layer protocol, for
example to IPv6. example to IPv6.
1.2. The EDNS protocol extension starting with version 0 permits larger The EDNS protocol extension starting with version 0 permits larger
responses by mutual agreement of the requester and responder (see responses by mutual agreement of the requester and responder (see
[RFC2671 2.3, 4.5]), and it is recommended to support EDNS. The 512 [RFC2671] 2.3, 4.5), and it is recommended to support EDNS. The 512
octets message size limit will remain in practical effect until octets UDP message size limit will remain in practical effect until
virtually all DNS servers and resolvers support EDNS. virtually all DNS servers and resolvers support EDNS.
1.3. Since DNS responses include a copy of the request, the space Since DNS responses include a copy of the request, the space
available for response data is somewhat less than the full 512 octets. available for response data is somewhat less than the full 512
Negative responses are quite small, but for positive and referral octets. Negative responses are quite small, but for positive and
responses, every octet must be carefully and sparingly allocated. While referral responses, every octet must be carefully and sparingly
the response size of positive responses is also a concern (see allocated. While the response size of positive responses is also a
[RFC3226]), this document specifically addresses referral response size. concern[RFC3226], this document specifically addresses referral
response size.
2 - Delegation Details 1.2. Requirements Language
2.1. RELEVANT PROTOCOL ELEMENTS The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.1.1. A delegation response will include the following elements: 2. Delegation Details
2.1. Relevant Protocol Elements
A delegation response will include the following elements:
Header Section: fixed length (12 octets) Header Section: fixed length (12 octets)
Question Section: original query (name, class, type) Question Section: original query (name, class, type)
Answer Section: empty, or a CNAME/DNAME chain Answer Section: empty, or a CNAME/DNAME chain
Authority Section: NS RRset (nameserver names) Authority Section: NS RRset (nameserver names)
Additional Section: A and AAAA RRsets (nameserver addresses) Additional Section: A and AAAA RRsets (nameserver addresses)
2.1.2. If the total response size exceeds 512 octets or advertised size If the total size of the UDP response exceeds 512 octets or
in EDNS, and if the data that does not fit was "required", then the TC advertised size in EDNS, and if the data that does not fit was
bit will be set (indicating truncation). This will usually cause the "required", then the TC bit will be set (indicating truncation).
requester to retry using TCP, depending on what information was desired This will usually cause the requester to retry using TCP, depending
and what information was omitted. For example, truncation in the on what information was desired and what information was omitted.
authority section is of no interest to a stub resolver who only plans to For example, truncation in the authority section is of no interest to
consume the answer section. If a retry using TCP is needed, the total a stub resolver who only plans to consume the answer section. If a
cost of the transaction is much higher. See [RFC1123 6.1.3.2] for retry using TCP is needed, the total cost of the transaction is much
details on the requirement that UDP be attempted before falling back to higher. See [RFC1123] 6.1.3.2 for details on the requirement that
TCP. UDP be attempted before falling back to TCP.
INTERNET-DRAFT November 19, 2007 RESPSIZE
2.1.3. RRsets are never sent partially unless the TC bit is set to RRsets are never sent partially unless the TC bit is set to indicate
indicate truncation. When TC bit is set, the final apparent RRset in truncation. When the TC bit is set, the final apparent RRset in the
the final non-empty section must be considered "possibly damaged" (see final non-empty section must be considered "possibly damaged" (see
[RFC1035 6.2], [RFC2181 9]). [RFC1035] 6.2, [RFC2181] 9).
2.1.4. With or without truncation, the glue present in the additional With or without truncation, the glue present in the additional data
data section should be considered "possibly incomplete", and requesters section should be considered "possibly incomplete", and requesters
should be prepared to re-query for any damaged or missing RRsets. Note should be prepared to re-query for any damaged or missing RRsets.
that truncation of the additional data section might not be signaled via Note that truncation of the additional data section might not be
the TC bit since additional data is often optional (see discussion in signaled via the TC bit since additional data is often optional (see
[RFC4472 B]). discussion in [RFC4472] B).
2.1.5. DNS label compression allows the component labels of a domain DNS label compression allows the component labels of a domain name to
name to be instantiated exactly once per DNS message, and then be instantiated exactly once per DNS message, and then referenced
referenced with a two-octet "pointer" from other locations in that same with a two-octet "pointer" from other locations in that same DNS
DNS message (see [RFC1035 4.1.4]). If all nameserver names in a message message (see [RFC1035] 4.1.4). If all nameserver names in a message
share a common parent (for example, all ending in ".ROOT-SERVERS.NET"), share a common parent (for example, all ending in ".ROOT-
then more space will be available for incompressible data (such as SERVERS.NET"), then more space will be available for incompressible
nameserver addresses). data (such as nameserver addresses).
2.1.6. The query name can be as long as 255 octets of network data. In The query name can be as long as 255 octets of network data. In this
this worst case scenario, the question section will be 259 octets in worst case scenario, the question section will be 259 octets in size,
size, which would leave only 240 octets for the authority and additional which would leave only 240 octets for the authority and additional
sections (after deducting 12 octets for the fixed length header) in a sections (after deducting 12 octets for the fixed length header) in a
referral. referral.
2.2. ADVICE TO ZONE OWNERS 2.2. Advice to Zone Owners
2.2.1. Average and maximum question section sizes can be predicted by Average and maximum question section sizes can be predicted by the
the zone owner, since they will know what names actually exist, and can zone owner, since they will know what names actually exist, and can
measure which ones are queried for most often. Note that if the zone measure which ones are queried for most often. Note that if the zone
contains any wildcards, it is possible for maximum length queries to contains any wildcards, it is possible for maximum length queries to
require positive responses, but that it is reasonable to expect require positive responses, but that it is reasonable to expect
truncation and TCP retry in that case. For cost and performance truncation and TCP retry in that case. For cost and performance
reasons, the majority of requests should be satisfied without truncation reasons, the majority of requests should be satisfied without
or TCP retry. truncation or TCP retry.
2.2.2. Some queries to non-existing names can be large, but this is not
a problem because negative responses need not contain any answer,
authority or additional records. See [RFC2308 2.1] for more information
about the format of negative responses.
2.2.3. The minimum useful number of name servers is two, for redundancy Some queries to non-existing names can be large, but this is not a
(see [RFC1034 4.1]). A zone's name servers should be reachable by all problem because negative responses need not contain any answer,
IP protocols (e.g., IPv4 and IPv6) in common use. As long as the authority or additional records. See [RFC2308] 2.1 for more
INTERNET-DRAFT November 19, 2007 RESPSIZE information about the format of negative responses.
servers are well managed, the server serving IPv6 might be different The minimum useful number of name servers is two, for redundancy (see
from the server serving IPv4 sharing the same server name. It is [RFC1034] 4.1). A zone's name servers should be reachable by all IP
important to ensure that a zone should have servers reachable by every protocols versions (e.g., IPv4 and IPv6) in common use. As long as
IP protocol in common use (e.g., IPv4 and IPv6). the servers are well managed, the server serving IPv6 might be
different from the server serving IPv4 sharing the same server name.
It is important to ensure that a zone should have servers reachable
by all IP protocol in common use (e.g., IPv4 and IPv6).
2.2.4. The best case is no truncation at all. This is because many The best case is no truncation at all. This is because many
requesters will retry using TCP immediately, or will automatically re- requesters will retry using TCP immediately, or will automatically
query for RRsets that are possibly truncated, without considering requery for RRsets that are possibly truncated, without considering
whether the omitted data was actually necessary. whether the omitted data was actually necessary.
2.2.5. Anycasting (see [RFC3258]) is a useful tool for performance and Anycasting[RFC3258] is a useful tool for performance and reliability
reliability without increasing the size of referral response. without increasing the size of referral response.
2.2.6. While it is irrelevant to the response size issue, all zones have While it is irrelevant to the response size issue, all zones have to
to be served in IPv4 as well to avoid name space fragmentation (see be served via IPv4 as well to avoid name space
[RFC3901]). fragmentation[RFC3901].
2.3. ADVICE TO SERVER IMPLEMENTORS 2.3. Advice to Server Implementors
2.3.1. Each added NS RR for a zone will add 12 fixed octets (name, type, Each NS RR for a zone will add 12 fixed octets (name, type, class,
class, ttl, and rdlen) plus 2 to 255 variable octets (for the NSDNAME). ttl, and rdlen) plus 2 to 255 variable octets (for the NSDNAME).
Each A RR will require 16 octets, and each AAAA RR will require 28 Each A RR will require 16 octets, and each AAAA RR will require 28
octets. octets.
2.3.2. While DNS distinguishes between necessary and optional resource While DNS distinguishes between necessary and optional resource
records, this distinction is according to protocol elements necessary to records, this distinction is according to protocol elements necessary
signify facts, and takes no official notice of protocol content to signify facts, and takes no official notice of protocol content
necessary to ensure correct operation. For example, a nameserver name necessary to ensure correct operation. For example, a nameserver
that is in or below the zone cut being described by a delegation is name that is in or below the zone cut being described by a delegation
"necessary content," since there is no way to reach that zone unless the is "necessary content", since there is no way to reach that zone
parent zone's delegation includes "glue records" describing that name unless the parent zone's delegation includes "glue records"
server's addresses. describing that name server's addresses.
2.3.3. Recall that the TC bit is only set when the required RRset can Recall that the TC bit is only set when the required RRset can not be
not be included in its entirety (see [RFC2181 9]). Even when some of the included in its entirety (see [RFC2181] 9). Even when some of the
RRsets to be included in the additional section are not fit in the RRsets to be included in the additional section are not fit in the
response size, TC bit isn't set. These RRsets may be important for a response size, the TC bit isn't set. These RRsets may be important
referral. Some DNS implementation tries to resolve these missing glue for a referral. Some DNS implementations try to resolve these
records separately which will introduce extra queries and extra time to missing glue records separately which will introduce extra queries
resolve a given name. and extra time to resolve a given name.
2.3.4. A delegation response should prioritize glue records as follows. A delegation response should prioritize glue records as follows.
first first:
All glue RRsets for one name server whose name is in or below the All glue RRsets for one name server whose name is in or below the
INTERNET-DRAFT November 19, 2007 RESPSIZE zone being delegated, or which has multiple address RRsets
(currently A and AAAA), or preferably both;
zone being delegated, or which has multiple address RRsets (currently second:
A and AAAA), or preferably both; Alternate between adding all glue RRsets for any name servers
whose names are in or below the zone being delegated, and all
second glue RRsets for any name servers who have multiple address RRsets
Alternate between adding all glue RRsets for any name servers whose (currently A and AAAA);
names are in or below the zone being delegated, and all glue RRsets thence:
for any name servers who have multiple address RRsets (currently A
and AAAA);
thence
All other glue RRsets, in any order. All other glue RRsets, in any order.
Whenever there are multiple candidates for a position in this priority Whenever there are multiple candidates for a position in this
scheme, one should be chosen on a round-robin or fully random basis. priority scheme, one should be chosen on a round-robin or fully
random basis. The goal of this priority scheme is to offer
The goal of this priority scheme is to offer "necessary" glue first, "necessary" glue first, avoiding silent truncation for this glue if
avoiding silent truncation for this glue if possible. possible.
2.3.5. If any "necessary content" is silently truncated, then it is
advisable that the TC bit be set in order to force a TCP retry, rather
than have the zone be unreachable. Note that a parent server's proper
response to a query for in-child glue or below-child glue is a referral
rather than an answer, and that this referral must be able to contain
the in-child or below-child glue, and that in outlying cases, only EDNS
or TCP will be large enough to contain that data.
3 - Analysis If any "necessary content" is silently truncated, then it is
advisable that the TC bit be set in order to force a TCP retry,
rather than have the zone be unreachable. Note that a parent
server's proper response to a query for in-child glue or below-child
glue is a referral rather than an answer, and that this referral must
be able to contain the in-child or below-child glue, and that in
outlying cases, only EDNS or TCP will be large enough to contain that
data.
3.1. An instrumented protocol trace of a best case delegation response 3. Analysis
follows. Note that 13 servers are named, and 13 addresses are given.
This query was artificially designed to exactly reach the 512 octets
limit.
INTERNET-DRAFT November 19, 2007 RESPSIZE An instrumented protocol trace of a best case delegation response is
shown in Figure 1. Note that 13 servers are named, and 13 addresses
are given. This query was artificially designed to exactly reach the
512 octets limit.
;; flags: qr rd; QUERY: 1, ANS: 0, AUTH: 13, ADDIT: 13 ;; flags: qr rd; QUERY: 1, ANS: 0, AUTH: 13, ADDIT: 13
;; QUERY SECTION: ;; QUERY SECTION:
;; [23456789.123456789.123456789.\ ;; [23456789.123456789.123456789.\
123456789.123456789.123456789.com A IN] ;; @80 123456789.123456789.123456789.com A IN] ;; @80
;; AUTHORITY SECTION: ;; AUTHORITY SECTION:
com. 86400 NS E.GTLD-SERVERS.NET. ;; @112 com. 86400 NS E.GTLD-SERVERS.NET. ;; @112
com. 86400 NS F.GTLD-SERVERS.NET. ;; @128 com. 86400 NS F.GTLD-SERVERS.NET. ;; @128
com. 86400 NS G.GTLD-SERVERS.NET. ;; @144 com. 86400 NS G.GTLD-SERVERS.NET. ;; @144
skipping to change at page 6, line 44 skipping to change at page 6, line 42
G.GTLD-SERVERS.NET. 86400 A 192.42.93.30 ;; @416 G.GTLD-SERVERS.NET. 86400 A 192.42.93.30 ;; @416
H.GTLD-SERVERS.NET. 86400 A 192.54.112.30 ;; @432 H.GTLD-SERVERS.NET. 86400 A 192.54.112.30 ;; @432
I.GTLD-SERVERS.NET. 86400 A 192.43.172.30 ;; @448 I.GTLD-SERVERS.NET. 86400 A 192.43.172.30 ;; @448
J.GTLD-SERVERS.NET. 86400 A 192.48.79.30 ;; @464 J.GTLD-SERVERS.NET. 86400 A 192.48.79.30 ;; @464
K.GTLD-SERVERS.NET. 86400 A 192.52.178.30 ;; @480 K.GTLD-SERVERS.NET. 86400 A 192.52.178.30 ;; @480
L.GTLD-SERVERS.NET. 86400 A 192.41.162.30 ;; @496 L.GTLD-SERVERS.NET. 86400 A 192.41.162.30 ;; @496
M.GTLD-SERVERS.NET. 86400 A 192.55.83.30 ;; @512 M.GTLD-SERVERS.NET. 86400 A 192.55.83.30 ;; @512
;; MSG SIZE sent: 80 rcvd: 512 ;; MSG SIZE sent: 80 rcvd: 512
3.2. For longer query names, the number of address records supplied will Figure 1
be lower. Furthermore, it is only by using a common parent name (which
is GTLD-SERVERS.NET in this example) that all 13 addresses are able to
fit, due to the use of DNS compression pointers in the last 12
occurrences of the parent domain name. The following output from a
response simulator written in perl [PERL] demonstrates these properties.
INTERNET-DRAFT November 19, 2007 RESPSIZE For longer query names, the number of address records supplied will
be lower. Furthermore, it is only by using a common parent name
(which is "GTLD-SERVERS.NET" in this example) that all 13 addresses
are able to fit, due to the use of DNS compression pointers in the
last 12 occurrences of the parent domain name. The following outputs
shown in Figure 2 and Figure 3 from a response simulator in
Appendix A written in perl[PERL] demonstrate these properties.
% perl respsize.pl a.dns.br b.dns.br c.dns.br d.dns.br % perl respsize.pl a.dns.br b.dns.br c.dns.br d.dns.br
a.dns.br requires 10 bytes a.dns.br requires 10 bytes
b.dns.br requires 4 bytes b.dns.br requires 4 bytes
c.dns.br requires 4 bytes c.dns.br requires 4 bytes
d.dns.br requires 4 bytes d.dns.br requires 4 bytes
# of NS: 4 # of NS: 4
For maximum size query (255 byte): For maximum size query (255 byte):
only A is considered: # of A is 4 (green) only A is considered: # of A is 4 (green)
A and AAAA are considered: # of A+AAAA is 3 (yellow) A and AAAA are considered: # of A+AAAA is 3 (yellow)
preferred-glue A is assumed: # of A is 4, # of AAAA is 3 (yellow) preferred-glue A is assumed: # of A is 4, # of AAAA is 3 (yellow)
For average size query (64 byte): For average size query (64 byte):
only A is considered: # of A is 4 (green) only A is considered: # of A is 4 (green)
A and AAAA are considered: # of A+AAAA is 4 (green) A and AAAA are considered: # of A+AAAA is 4 (green)
preferred-glue A is assumed: # of A is 4, # of AAAA is 4 (green) preferred-glue A is assumed: # of A is 4, # of AAAA is 4 (green)
Figure 2
% perl respsize.pl ns-ext.isc.org ns.psg.com ns.ripe.net ns.eu.int % perl respsize.pl ns-ext.isc.org ns.psg.com ns.ripe.net ns.eu.int
ns-ext.isc.org requires 16 bytes ns-ext.isc.org requires 16 bytes
ns.psg.com requires 12 bytes ns.psg.com requires 12 bytes
ns.ripe.net requires 13 bytes ns.ripe.net requires 13 bytes
ns.eu.int requires 11 bytes ns.eu.int requires 11 bytes
# of NS: 4 # of NS: 4
For maximum size query (255 byte): For maximum size query (255 byte):
only A is considered: # of A is 4 (green) only A is considered: # of A is 4 (green)
A and AAAA are considered: # of A+AAAA is 3 (yellow) A and AAAA are considered: # of A+AAAA is 3 (yellow)
preferred-glue A is assumed: # of A is 4, # of AAAA is 2 (yellow) preferred-glue A is assumed: # of A is 4, # of AAAA is 2 (yellow)
For average size query (64 byte): For average size query (64 byte):
only A is considered: # of A is 4 (green) only A is considered: # of A is 4 (green)
A and AAAA are considered: # of A+AAAA is 4 (green) A and AAAA are considered: # of A+AAAA is 4 (green)
preferred-glue A is assumed: # of A is 4, # of AAAA is 4 (green) preferred-glue A is assumed: # of A is 4, # of AAAA is 4 (green)
(Note: The response simulator program is shown in Appendix A.) Figure 3
Here we use the term "green" if all address records could fit, or Here we use the term "green" if all address records could fit, or
"yellow" if two or more could fit, or "orange" if only one could fit, or "yellow" if two or more could fit, or "orange" if only one could fit,
"red" if no address record could fit. It's clear that without a common or "red" if no address record could fit. It's clear that without a
parent for nameserver names, much space would be lost. For these common parent for nameserver names, much space would be lost. For
examples we use an average/common name size of 15 octets, befitting our these examples we use an average/common name size of 15 octets,
assumption of GTLD-SERVERS.NET as our common parent name. befitting our assumption of GTLD-SERVERS.NET as our common parent
name.
We're assuming a medium query name size of 64 since that is the typical We're assuming a medium query name size of 64 since that is the
size seen in trace data at the time of this writing. If typical size seen in trace data at the time of this writing. If
Internationalized Domain Name (IDN) or any other technology which Internationalized Domain Name (IDN) or any other technology which
results in larger query names be deployed significantly in advance of results in larger query names be deployed significantly in advance of
EDNS, then new measurements and new estimates will have to be made. EDNS, then new measurements and new estimates will have to be made.
INTERNET-DRAFT November 19, 2007 RESPSIZE 4. Conclusions
4 - Conclusions
4.1. The current practice of giving all nameserver names a common parent The current practice of giving all nameserver names a common parent
(such as GTLD-SERVERS.NET or ROOT-SERVERS.NET) saves space in DNS (such as GTLD-SERVERS.NET or ROOT-SERVERS.NET) saves space in DNS
responses and allows for more nameservers to be enumerated than would responses and allows for more nameservers to be enumerated than would
otherwise be possible, since the common parent domain name only appears otherwise be possible, since the common parent domain name only
once in a DNS message and is referred to via "compression pointers" appears once in a DNS message and is referred to via "compression
thereafter. pointers" thereafter.
4.2. If all nameserver names for a zone share a common parent, then it If all nameserver names for a zone share a common parent, then it is
is operationally advisable to make all servers for the zone thus served operationally advisable to make all servers for the zone thus served
also be authoritative for the zone of that common parent. For example, also be authoritative for the zone of that common parent. For
the root name servers (?.ROOT-SERVERS.NET) can answer authoritatively example, the root name servers (?.ROOT-SERVERS.NET) can answer
for the ROOT-SERVERS.NET. This is to ensure that the zone's servers authoritatively for the ROOT-SERVERS.NET zone. This is to ensure
always have the zone's nameservers' glue available when delegating, and that the zone's servers always have the zone's nameservers' glue
will be able to respond with answers rather than referrals if a available when delegating, and will be able to respond with answers
requester who wants that glue comes back asking for it. In this case rather than referrals if a requester who wants that glue comes back
the name server will likely be a "stealth server" -- authoritative but asking for it. In this case the name server will likely be a
unadvertised in the glue zone's NS RRset. See [RFC1996 2] for more "stealth server" -- authoritative but unadvertised in the glue zone's
information about stealth servers. NS RRset. See [RFC1996] 2 for more information about stealth
servers.
4.3. Thirteen (13) is the effective maximum number of nameserver names Thirteen (13) is the effective maximum number of nameserver names
usable traditional (non-extended) DNS, assuming a common parent domain usable with traditional (non-extended) DNS, assuming a common parent
name, and given that implicit referral response truncation is domain name, and given that implicit referral response truncation is
undesirable in the average case. undesirable in the average case.
4.4. More than one address records in a protocol family per a server is More than one address records in a protocol family per a server is
inadvisable since the necessary glue RRsets (A or AAAA) are atomically inadvisable since the necessary glue RRsets (A or AAAA) are
indivisible, and will be larger than a single resource record. Larger atomically indivisible, and will be larger than a single resource
RRsets are more likely to lead to or encounter truncation. record. Larger RRsets are more likely to lead to or encounter
truncation.
4.5. More than one address records across protocol families is less More than one address records across protocol families is less likely
likely to lead to or encounter truncation, partly because multiprotocol to lead to or encounter truncation, partly because multiprotocol
clients, which are required to handle larger RRsets such as AAAA RRs, clients, which are required to handle larger RRsets such as AAAA RRs,
are more likely to speak EDNS which can use a larger response size are more likely to speak EDNS which can use a larger UDP response
limit, and partly because the resource records (A and AAAA) are in size limit, and partly because the resource records (A and AAAA) are
different RRsets and are therefore divisible from each other. in different RRsets and are therefore divisible from each other.
4.6. Name server names which are at or below the zone they serve are
more sensitive to referral response truncation, and glue records for
them should be considered "more important" than other glue records, in
the assembly of referral responses.
4.7. If a zone is served by thirteen (13) name servers having a common Name server names which are at or below the zone they serve are more
parent name (such as ?.ROOT-SERVERS.NET) and each such name server has a sensitive to referral response truncation, and glue records for them
INTERNET-DRAFT November 19, 2007 RESPSIZE should be considered "more important" than other glue records, in the
assembly of referral responses.
single address record in some protocol family (e.g., an A RR), then all If a zone is served by thirteen (13) name servers having a common
thirteen name servers or any subset thereof could have address records parent name (such as ?.ROOT-SERVERS.NET) and each such name server
in a second protocol family by adding a second address record (e.g., an has a single address record in some protocol family (e.g., an A RR),
AAAA RR) without reducing the reachability of the zone thus served. then all thirteen name servers or any subset thereof could have
address records in a second protocol family by adding a second
address record (e.g., an AAAA RR) without reducing the reachability
of the zone thus served.
5 - Security Considerations 5. Security Considerations
The recommendations contained in this document have no known security The recommendations contained in this document have no known security
implications. implications.
6 - IANA Considerations 6. IANA Considerations
This document does not call for changes or additions to any IANA This document does not call for changes or additions to any IANA
registry. registry.
7 - Acknowledgement 7. Acknowledgement
The authors thank Peter Koch, Rob Austein, Joe Abley, Mark Andrews, The authors thank Peter Koch, Rob Austein, Joe Abley, Mark Andrews,
Kenji Rikitake, Stephane Bortzmeyerand Olafur Gudmundsson for their Kenji Rikitake, Stephane Bortzmeyerand, Olafur Gudmundsson, and
valuable comments and suggestions. Alfred Hines for their valuable comments and suggestions.
This work was supported by the US National Science Foundation (research This work was supported by the US National Science Foundation
grant SCI-0427144) and DNS-OARC. (research grant SCI-0427144) and DNS-OARC.
8 - References 8. Normative References
[RFC1034] Mockapetris, P.V., "Domain names - Concepts and Facilities", [PERL] Wall, L., Christiansen, T., and j. Orwant, "Programing
RFC1034, November 1987. Perl", July 2000.
[RFC1035] Mockapetris, P.V., "Domain names - Implementation and [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
Specification", RFC1035, November 1987. STD 13, RFC 1034, November 1987.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1035] Mockapetris, P., "Domain names - implementation and
Application and Support", RFC1123, October 1989. specification", STD 13, RFC 1035, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC1996, August 1996. Changes (DNS NOTIFY)", RFC1996, August 1996.
[RFC2181] Elz, R., Bush, R., "Clarifications to the DNS Specification", [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
RFC2181, July 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
RFC2308, March 1998. Specification", RFC 2181, July 1997.
INTERNET-DRAFT November 19, 2007 RESPSIZE [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC2671, [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
August 1999. RFC 2671, August 1999.
[RFC3226] Gudmundsson, O., "DNSSEC and IPv6 A6 aware server/resolver [RFC3226] Gudmundsson, O., "DNSSEC and IPv6 A6 aware server/resolver
message size requirements", RFC3226, December 2001. message size requirements", RFC3226, December 2001.
[RFC3258] Hardie, T., "Distributing Authoritative Name Servers via [RFC3258] Hardie, T., "Distributing Authoritative Name Servers via
Shared Unicast Addresses", RFC3258, April 2002. Shared Unicast Addresses", RFC3258, April 2002.
[RFC3901] Durand, A., Ihren, J., "DNS IPv6 Transport Operational [RFC3901] Durand, A. and J. Ihren, "DNS IPv6 Transport Operational
Guidelines", RFC3901, September 2004. Guidelines", BCP 91, RFC 3901, September 2004.
[RFC4472] Durand, A., Ihren, J., Savola, P., "Operational Consideration
and Issues with IPV6 DNS", RFC4472, April 2006.
[PERL] Wall, L., Christiansen, T., Orwant, J., "Programming Perl",
O'Reilly, ISBN 0-596-00027-8, July 2000.
9 - Authors' Addresses
Paul Vixie
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
+1 650 423 1301
vixie@isc.org
Akira Kato [RFC4472] Durand, A., Ihren, J., and P. Savola, "Operational
University of Tokyo, Information Technology Center Considerations and Issues with IPv6 DNS", RFC 4472,
2-11-16 Yayoi Bunkyo April 2006.
Tokyo 113-8658, JAPAN
+81 3 5841 2750
kato@wide.ad.jp
Appendix A - Source Code Appendix A. The response simulator program
#!/usr/bin/perl #!/usr/bin/perl
# #
# SYNOPSIS # SYNOPSIS
# respsize.pl [ -z zone ] fqdn_ns1 fqdn_ns2 ... # respsize.pl [ -z zone ] fqdn_ns1 fqdn_ns2 ...
# if all queries are assumed to have a same zone suffix, # if all queries are assumed to have a same zone suffix,
# such as "jp" in JP TLD servers, specify it in -z option # such as "jp" in JP TLD servers, specify it in -z option
# #
use strict; use strict;
use Getopt::Std; use Getopt::Std;
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my ($sz_msg) = (512); my ($sz_msg) = (512);
my ($sz_header, $sz_ptr, $sz_rr_a, $sz_rr_aaaa) = (12, 2, 16, 28); my ($sz_header, $sz_ptr, $sz_rr_a, $sz_rr_aaaa) = (12, 2, 16, 28);
my ($sz_type, $sz_class, $sz_ttl, $sz_rdlen) = (2, 2, 4, 2); my ($sz_type, $sz_class, $sz_ttl, $sz_rdlen) = (2, 2, 4, 2);
my (%namedb, $name, $nssect, %opts, $optz); my (%namedb, $name, $nssect, %opts, $optz);
my $n_ns = 0; my $n_ns = 0;
getopt('z', %opts); getopt('z', %opts);
if (defined($opts{'z'})) { if (defined($opts{'z'})) {
server_name_len($opts{'z'}); # just register it server_name_len($opts{'z'}); # just register it
skipping to change at page 12, line 4 skipping to change at page 11, line 40
} }
return $len; return $len;
} }
sub arsect { sub arsect {
my ($sz_query, $nssect, $n_ns, $cond) = @_; my ($sz_query, $nssect, $n_ns, $cond) = @_;
my ($space, $n_a, $n_a_aaaa, $n_p_aaaa, $ansect); my ($space, $n_a, $n_a_aaaa, $n_p_aaaa, $ansect);
$ansect = $sz_query + $sz_type + $sz_class; $ansect = $sz_query + $sz_type + $sz_class;
$space = $sz_msg - $sz_header - $ansect - $nssect; $space = $sz_msg - $sz_header - $ansect - $nssect;
$n_a = atmost(int($space / $sz_rr_a), $n_ns); $n_a = atmost(int($space / $sz_rr_a), $n_ns);
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$n_a_aaaa = atmost(int($space $n_a_aaaa = atmost(int($space
/ ($sz_rr_a + $sz_rr_aaaa)), $n_ns); / ($sz_rr_a + $sz_rr_aaaa)), $n_ns);
$n_p_aaaa = atmost(int(($space - $sz_rr_a * $n_ns) $n_p_aaaa = atmost(int(($space - $sz_rr_a * $n_ns)
/ $sz_rr_aaaa), $n_ns); / $sz_rr_aaaa), $n_ns);
printf "For %s size query (%d byte):\n", $cond, $sz_query; printf "For %s size query (%d byte):\n", $cond, $sz_query;
printf " only A is considered: "; printf " only A is considered: ";
printf "# of A is %d (%s)\n", $n_a, &judge($n_a, $n_ns); printf "# of A is %d (%s)\n", $n_a, &judge($n_a, $n_ns);
printf " A and AAAA are considered: "; printf " A and AAAA are considered: ";
printf "# of A+AAAA is %d (%s)\n", printf "# of A+AAAA is %d (%s)\n",
$n_a_aaaa, &judge($n_a_aaaa, $n_ns); $n_a_aaaa, &judge($n_a_aaaa, $n_ns);
skipping to change at page 12, line 36 skipping to change at page 12, line 22
return "red"; return "red";
} }
sub atmost { sub atmost {
my ($a, $b) = @_; my ($a, $b) = @_;
return 0 if ($a < 0); return 0 if ($a < 0);
return $b if ($a > $b); return $b if ($a > $b);
return $a; return $a;
} }
Authors' Addresses
Paul Vixie
Internet Systems Consortium
950 Charter Street
Redwood City, CA 94063
US
Phone: +1 650 423 1300
Email: paul@vix.com
Akira Kato
The University of Tokyo/WIDE Project
Information Technology Center, 2-11-16 Yayoi
Bunkyo, Tokyo 113-8658
JP
Phone: +81 3 5841 2750
Email: kato@wide.ad.jp
Full Copyright Statement Full Copyright Statement
Copyright (C) IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors retain contained in BCP 78, and except as set forth therein, the authors
all their rights. retain all their rights.
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 OR "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST, AND THE OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE 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.
INTERNET-DRAFT November 19, 2007 RESPSIZE
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Acknowledgement Acknowledgment
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