draft-ietf-dnsop-respsize-04.txt   draft-ietf-dnsop-respsize-05.txt 
DNSOP Working Group Paul Vixie, ISC DNSOP Working Group Paul Vixie, ISC
INTERNET-DRAFT Akira Kato, WIDE INTERNET-DRAFT Akira Kato, WIDE
DNS Response Size Issues <draft-ietf-dnsop-respsize-05.txt> August 2006
DNS Referral Response Size Issues
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
skipping to change at page 1, line 39 skipping to change at page 1, line 41
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). All Rights Reserved. Copyright (C) The Internet Society (2006). All Rights Reserved.
Abstract Abstract
With a mandated default minimum maximum message size of 512 octets, With a mandated default minimum maximum message size of 512 octets,
the DNS protocol presents some special problems for zones wishing to the DNS protocol presents some special problems for zones wishing to
expose a moderate or high number of authority servers (NS RRs). This expose a moderate or high number of authority servers (NS RRs). This
document explains the operational issues caused by, or related to document explains the operational issues caused by, or related to
this response size limit. this response size limit, and suggests ways to optimize the use of
this limited space. Guidance is offered to DNS server implementors
and to DNS zone operators.
INTERNET-DRAFT July 2006 RESPSIZE INTERNET-DRAFT August 2006 RESPSIZE
1 - Introduction and Overview 1 - Introduction and Overview
1.1. The DNS standard (see [RFC1035 4.2.1]) limits message size to 512 1.1. The DNS standard (see [RFC1035 4.2.1]) limits message size to 512
octets. Even though this limitation was due to the required minimum IP octets. Even though this limitation was due to the required minimum IP
reassembly limit for IPv4, it became a hard DNS protocol limit and is reassembly limit for IPv4, it became a hard DNS protocol limit and is
not implicitly relaxed by changes in transport, for example to IPv6. not implicitly relaxed by changes in transport, for example to IPv6.
1.2. The EDNS0 protocol extension (see [RFC2671 2.3, 4.5]) permits 1.2. The EDNS0 protocol extension (see [RFC2671 2.3, 4.5]) permits
larger responses by mutual agreement of the requestor and responder. larger responses by mutual agreement of the requester and responder.
However, deployment of EDNS0 cannot be expected to reach every Internet The 512 octet message size limit will remain in practical effect until
resolver in the short or medium term. The 512 octet message size limit there is widespread deployment of EDNS0 in DNS resolvers on the
remains in practical effect at this time. Internet.
1.3. Since DNS responses include a copy of the request, the space 1.3. 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 octets.
Negative responses are quite small, but for positive and delegation Negative responses are quite small, but for positive and delegation
responses, every octet must be carefully and sparingly allocated. This responses, every octet must be carefully and sparingly allocated. This
document specifically addresses delegation response sizes. document specifically addresses delegation response sizes.
2 - Delegation Details 2 - Delegation Details
2.1. A delegation response will include the following elements: 2.1. RELEVANT PROTOCOL ELEMENTS
2.1.1. 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) Answer Section: (empty)
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)
2.2. If the total response size would exceed 512 octets, and if the data 2.1.2. If the total response size exceeds 512 octets, and if the data
that would not fit was "required", then the TC bit will be set that does not fit was "required", then the TC bit will be set
(indicating truncation). This will usually cause the requestor to retry (indicating truncation). This will usually cause the requester to retry
using TCP, depending on what information was desired and what using TCP, depending on what information was desired and what
information was omitted. (For example, truncation in the authority information was omitted. For example, truncation in the authority
section is of no interest to a stub resolver who only plans to consume section is of no interest to a stub resolver who only plans to consume
the answer section.) If a retry using TCP is needed, the total cost of the answer section. If a retry using TCP is needed, the total cost of
the transaction is much higher. See [RFC1123 6.1.3.2] for details on the transaction is much higher. See [RFC1123 6.1.3.2] for details on
the requirement that UDP be attempted before falling back to TCP. the requirement that UDP be attempted before falling back to TCP.
2.3. RRsets are never sent partially unless TC bit set to indicate 2.1.3. RRsets are never sent partially unless TC bit set to indicate
truncation. When TC bit is set, the final apparent RRset in the final truncation. When TC bit is set, the final apparent RRset in the final
nonempty section must be considered "possibly damaged" (see [RFC1035 non-empty section must be considered "possibly damaged" (see [RFC1035
6.2], [RFC2181 9]). 6.2], [RFC2181 9]).
INTERNET-DRAFT July 2006 RESPSIZE INTERNET-DRAFT August 2006 RESPSIZE
2.4. With or without truncation, the glue present in the additional data 2.1.4. With or without truncation, the glue present in the additional
section should be considered "possibly incomplete", and requestors data 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. Note
that truncation of the additional data section might not be signalled that truncation of the additional data section might not be signalled
via the TC bit since additional data is often optional. via the TC bit since additional data is often optional.
2.5. DNS label compression allows a domain name to be instantiated only 2.1.5. DNS label compression allows a domain name to be instantiated
once per DNS message, and then referenced with a two-octet "pointer" only once per DNS message, and then referenced with a two-octet
from other locations in that same DNS message. If all nameserver names "pointer" from other locations in that same DNS message (see [RFC1035
in a message are similar (for example, all ending in ".ROOT- 4.1.4]). If all nameserver names in a message share a common parent
SERVERS.NET"), then more space will be available for uncompressable data (for example, all ending in ".ROOT-SERVERS.NET"), then more space will
(such as nameserver addresses). be available for incompressable data (such as nameserver addresses).
2.6. The query name can be as long as 255 characters of presentation 2.1.6. The query name can be as long as 255 characters of presentation
data, which can be up to 256 octets of network data. In this worst case data, which can be up to 256 octets of network data. In this worst case
scenario, the question section will be 260 octets in size, which would scenario, the question section will be 260 octets in size, which would
leave only 240 octets for the authority and additional sections (after leave only 240 octets for the authority and additional sections (after
deducting 12 octets for the fixed length header.) deducting 12 octets for the fixed length header.)
2.7. Average and maximum question section sizes can be predicted by the 2.2. ADVICE TO ZONE OWNERS
zone owner, since they will know what names actually exist, and can
measure which ones are queried for most often. For cost and performance 2.2.1. Average and maximum question section sizes can be predicted by
the 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
contains any wildcards, it is possible for maximum length queries to
require positive responses, but that it is reasonable to expect
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 truncation
or TCP retry. or TCP retry.
2.8. Some queries to non-existing names can be large, but this is not a 2.2.2. Some queries to non-existing names can be large, but this is not
problem because negative responses need not contain any answer, a problem because negative responses need not contain any answer,
authority or additional records. (See [RFC2308 2.1] for more authority or additional records. See [RFC2308 2.1] for more information
information about the format of negative responses.) about the format of negative responses.
2.9. The minimum useful number of name servers is two, for redundancy 2.2.3. The minimum useful number of name servers is two, for redundancy
(see [RFC1034 4.1]). In case of multihomed name servers, it is (see [RFC1034 4.1]). A zone's name servers should be reachable by all
advantageous to include an address record from each of several name IP transport protocols (e.g., IPv4 and IPv6) in common use.
servers before including several address records for any one name
server. If address records for more than one transport (for example, A
and AAAA) are available, then it is advantageous to include records of
both types early on, before the message is full.
2.10. The best case is no truncation at all. This is because many 2.2.4. The best case is no truncation at all. This is because many
requestors will retry using TCP by reflex, or will automatically re- requesters will retry using TCP by reflex, or will automatically re-
query for RRsets that are "possibly truncated", without considering query for RRsets that are possibly truncated, without considering
whether the omitted data was actually necessary. whether the omitted data was actually necessary.
2.11. Each added NS RR for a zone will add a minimum of between 16 and INTERNET-DRAFT August 2006 RESPSIZE
44 octets to every untruncated referral or negative response from the
INTERNET-DRAFT July 2006 RESPSIZE
zone's authority servers (16 octets for an NS RR, 16 octets for an A RR, 2.3. ADVICE TO SERVER IMPLEMENTORS
and 28 octets for an AAAA RR), in addition to whatever space is taken by
the nameserver name (NS NSDNAME as well as A or AAAA owner name).
2.12. While DNS distinguishes between necessary and optional resource 2.3.1. In case of multi-homed name servers, it is advantageous to
include an address record from each of several name servers before
including several address records for any one name server. If address
records for more than one transport (for example, A and AAAA) are
available, then it is advantageous to include records of both types
early on, before the message is full.
2.3.2. Each added NS RR for a zone will add between 16 and 44 octets to
every non-truncated referral or negative response from the zone's
authority servers (16 octets for an NS RR, 16 octets for an A RR, and 28
octets for an AAAA RR), in addition to whatever space is taken by the
nameserver name (NS NSDNAME as well as A or AAAA owner name).
2.3.3. 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 to
signify facts, and takes no official notice of protocol content 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 name
that is in or below the zone cut being described by a delegation is that is in or below the zone cut being described by a delegation is
"necessary content," since there is no way to reach that zone unless the "necessary content," since there is no way to reach that zone unless the
parent zone's delegation includes "glue records" describing that name parent zone's delegation includes "glue records" describing that name
server's addresses. server's addresses.
2.13. It is also necessary to distinguish between "explicit truncation" 2.3.4. It is also necessary to distinguish between "explicit truncation"
where a message could not contain enough records to convey its intended where a message could not contain enough records to convey its intended
meaning, and so the TC bit has been set, and "silent truncation", where meaning, and so the TC bit has been set, and "silent truncation", where
the message was not large enough to contain some records which were "not the message was not large enough to contain some records which were "not
required", and so the TC bit was not set. required", and so the TC bit was not set.
2.14. An delegation response should prioritize glue records as follows. 2.3.5. 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
zone being delegated, or which has multiple address RRsets (currently zone being delegated, or which has multiple address RRsets (currently
A and AAAA), or preferrably both; A and AAAA), or preferably both;
second second
Alternate between adding all glue RRsets for any name servers whose Alternate between adding all glue RRsets for any name servers whose
names are in or below the zone being delegated, and all glue RRsets names are in or below the zone being delegated, and all glue RRsets
for any name servers who have multiple address RRsets (currently A for any name servers who have multiple address RRsets (currently A
and AAAA); and AAAA);
thence thence
All other glue RRsets, in any order. All other glue RRsets, in any order.
INTERNET-DRAFT August 2006 RESPSIZE
Whenever there are multiple candidates for a position in this priority
scheme, one should be chosen on a round-robin or fully random basis.
The goal of this priority scheme is to offer "necessary" glue first, The goal of this priority scheme is to offer "necessary" glue first,
avoiding silent truncation for this glue if possible. avoiding silent truncation for this glue if possible.
2.15. If any "necessary content" is silently truncated, then it is 2.3.6. 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 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 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 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 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 the in-child or below-child glue, and that in outlying cases, only EDNS
or TCP will be large enough to contain that data. or TCP will be large enough to contain that data.
INTERNET-DRAFT July 2006 RESPSIZE
3 - Analysis 3 - Analysis
3.1. An instrumented protocol trace of a best case delegation response 3.1. An instrumented protocol trace of a best case delegation response
follows. Note that 13 servers are named, and 13 addresses are given. follows. Note that 13 servers are named, and 13 addresses are given.
This query was artificially designed to exactly reach the 512 octet This query was artificially designed to exactly reach the 512 octet
limit. 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.\
skipping to change at page 5, line 33 skipping to change at page 6, line 4
com. 86400 NS H.GTLD-SERVERS.NET. ;; @160 com. 86400 NS H.GTLD-SERVERS.NET. ;; @160
com. 86400 NS I.GTLD-SERVERS.NET. ;; @176 com. 86400 NS I.GTLD-SERVERS.NET. ;; @176
com. 86400 NS J.GTLD-SERVERS.NET. ;; @192 com. 86400 NS J.GTLD-SERVERS.NET. ;; @192
com. 86400 NS K.GTLD-SERVERS.NET. ;; @208 com. 86400 NS K.GTLD-SERVERS.NET. ;; @208
com. 86400 NS L.GTLD-SERVERS.NET. ;; @224 com. 86400 NS L.GTLD-SERVERS.NET. ;; @224
com. 86400 NS M.GTLD-SERVERS.NET. ;; @240 com. 86400 NS M.GTLD-SERVERS.NET. ;; @240
com. 86400 NS A.GTLD-SERVERS.NET. ;; @256 com. 86400 NS A.GTLD-SERVERS.NET. ;; @256
com. 86400 NS B.GTLD-SERVERS.NET. ;; @272 com. 86400 NS B.GTLD-SERVERS.NET. ;; @272
com. 86400 NS C.GTLD-SERVERS.NET. ;; @288 com. 86400 NS C.GTLD-SERVERS.NET. ;; @288
com. 86400 NS D.GTLD-SERVERS.NET. ;; @304 com. 86400 NS D.GTLD-SERVERS.NET. ;; @304
INTERNET-DRAFT August 2006 RESPSIZE
;; ADDITIONAL SECTION: ;; ADDITIONAL SECTION:
A.GTLD-SERVERS.NET. 86400 A 192.5.6.30 ;; @320 A.GTLD-SERVERS.NET. 86400 A 192.5.6.30 ;; @320
B.GTLD-SERVERS.NET. 86400 A 192.33.14.30 ;; @336 B.GTLD-SERVERS.NET. 86400 A 192.33.14.30 ;; @336
C.GTLD-SERVERS.NET. 86400 A 192.26.92.30 ;; @352 C.GTLD-SERVERS.NET. 86400 A 192.26.92.30 ;; @352
D.GTLD-SERVERS.NET. 86400 A 192.31.80.30 ;; @368 D.GTLD-SERVERS.NET. 86400 A 192.31.80.30 ;; @368
E.GTLD-SERVERS.NET. 86400 A 192.12.94.30 ;; @384 E.GTLD-SERVERS.NET. 86400 A 192.12.94.30 ;; @384
F.GTLD-SERVERS.NET. 86400 A 192.35.51.30 ;; @400 F.GTLD-SERVERS.NET. 86400 A 192.35.51.30 ;; @400
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
INTERNET-DRAFT July 2006 RESPSIZE
3.2. For longer query names, the number of address records supplied will 3.2. For longer query names, the number of address records supplied will
be lower. Furthermore, it is only by using a common parent name (which 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 is GTLD-SERVERS.NET in this example) that all 13 addresses are able to
fit. The following output from a response simulator demonstrates these fit, due to the use of DNS compression pointers in the last 12
properties: occurances of the parent domain name. The following output from a
response simulator demonstrates 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)
INTERNET-DRAFT August 2006 RESPSIZE
% 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)
skipping to change at page 7, line 5 skipping to change at page 7, line 30
(Note: The response simulator program is shown in Section 5.) (Note: The response simulator program is shown in Section 5.)
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, or
"red" if no address record could fit. It's clear that without a common "red" if no address record could fit. It's clear that without a common
parent for nameserver names, much space would be lost. For these parent for nameserver names, much space would be lost. For these
examples we use an average/common name size of 15 octets, befitting our examples we use an average/common name size of 15 octets, befitting our
assumption of GTLD-SERVERS.NET as our common parent name. assumption of GTLD-SERVERS.NET as our common parent name.
INTERNET-DRAFT July 2006 RESPSIZE We're assuming a medium query name size of 64 since that is the typical
size seen in trace data at the time of this writing. If
We're assuming an average query name size of 64 since that is the Internationalized Domain Name (IDN) or any other technology which
typical average maximum size seen in trace data at the time of this results in larger query names be deployed significantly in advance of
writing. If Internationalized Domain Name (IDN) or any other technology EDNS, then new measurements and new estimates will have to be made.
which results in larger query names be deployed significantly in advance
of EDNS, then new measurements and new estimates will have to be made.
4 - Conclusions 4 - Conclusions
4.1. The current practice of giving all nameserver names a common parent 4.1. 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 appears
once in a DNS message and is referred to via "compression pointers" once in a DNS message and is referred to via "compression pointers"
thereafter. thereafter.
4.2. If all nameserver names for a zone share a common parent, then it 4.2. If all nameserver names for a zone share a common parent, then it
is operationally advisable to make all servers for the zone so served is 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 example,
the root name servers (?.ROOT-SERVERS.NET) can answer authoritatively the root name servers (?.ROOT-SERVERS.NET) can answer authoritatively
for the ROOT-SERVERS.NET. This is to ensure that the zone's servers for the ROOT-SERVERS.NET. This is to ensure that the zone's servers
always have the zone's nameservers' glue available when delegating. always have the zone's nameservers' glue available when delegating, and
INTERNET-DRAFT August 2006 RESPSIZE
4.3. Thirteen (13) seems to be the effective maximum number of will be able to respond with answers rather than referrals if a
nameserver names usable traditional (non-extended) DNS, assuming a requester who wants that glue comes back asking for it. In this case
common parent domain name, and given that response truncation is the name server will likely be a "stealth server" -- authoritative but
undesirable as an average case, and assuming mostly IPv4-only unadvertised in the glue zone's NS RRset. See [RFC1996 2] for more
reachability (only A RRs exist, not AAAA RRs). information about stealth servers.
XXX 4.4. Adding up to five IPv6 nameserver address records (AAAA RRs) to 4.3. Thirteen (13) is the effective maximum number of nameserver names
a prototypical delegation that currently contains thirteen (13) IPv4 usable traditional (non-extended) DNS, assuming a common parent domain
nameserver addresses (A RRs) for thirteen (13) nameserver names under a name, and given that implicit referral response truncation is
common parent, would not have a significant negative operational impact undesirable in the average case.
on the domain name system.
4.4. Multi-homing of name servers within a protocol family is
inadvisable since the necessary glue RRsets (A or AAAA) are atomically
indivisible, and will be larger than a single resource record. Larger
RRsets are more likely to lead to or encounter truncation.
4.5. Multi-homing of name servers across protocol families is less
likely to lead to or encounter truncation, partly because multiprotocol
clients are more likely to speak EDNS which can use a larger response
size limit, and partly because the resource records (A and AAAA) are 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 "less optional" 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
parent name (such as ?.ROOT-SERVERS.NET) and each such name server has a
single address record in some protocol family (e.g., an A RR), then all
thirteen name servers or any subset thereof could multi-home 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 - Source Code 5 - Source Code
#!/usr/bin/perl #!/usr/bin/perl
# #
# SYNOPSIS # SYNOPSIS
# repsize.pl [ -z zone ] fqdn_ns1 fqdn_ns2 ... # repsize.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;
INTERNET-DRAFT July 2006 RESPSIZE INTERNET-DRAFT August 2006 RESPSIZE
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 9, line 4 skipping to change at page 10, line 4
} }
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 + 1 + $sz_type + $sz_class; $ansect = $sz_query + 1 + $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);
INTERNET-DRAFT July 2006 RESPSIZE INTERNET-DRAFT August 2006 RESPSIZE
$n_a_aaaa = atmost(int($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",
skipping to change at page 9, line 46 skipping to change at page 10, line 46
6 - Security Considerations 6 - Security Considerations
The recommendations contained in this document have no known security The recommendations contained in this document have no known security
implications. implications.
7 - IANA Considerations 7 - 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.
8 - Acknowledgement The authors thank Peter Koch and Rob Austein for 8 - Acknowledgement
their valuable comments and suggestions.
INTERNET-DRAFT July 2006 RESPSIZE The authors thank Peter Koch, Rob Austein, and Joe Abley for their
valuable comments and suggestions.
9 - Refrenaces INTERNET-DRAFT August 2006 RESPSIZE
This work was supported by the US National Science Foundation (research
grant SCI-0427144) and DNS-OARC.
9 - References
[RFC1034] Mockapetris, P.V., "Domain names - Concepts and Facilities", [RFC1034] Mockapetris, P.V., "Domain names - Concepts and Facilities",
RFC1034, November 1987. RFC1034, November 1987.
[RFC1035] Mockapetris, P.V., "Domain names - Implementation and [RFC1035] Mockapetris, P.V., "Domain names - Implementation and
Specification", RFC1035, November 1987. Specification", RFC1035, November 1987.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", RFC1123, October 1989. Application and Support", RFC1123, October 1989.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC1996, August 1996.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)",
RFC2308, March 1998. RFC2308, March 1998.
[RFC2181] Elz, R., Bush, R., "Clarifications to the DNS Specification", [RFC2181] Elz, R., Bush, R., "Clarifications to the DNS Specification",
RFC2181, July 1997. RFC2181, July 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC2671, [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC2671,
August 1999. August 1999.
INTERNET-DRAFT July 2006 RESPSIZE
10 - Authors' Addresses 10 - Authors' Addresses
Paul Vixie Paul Vixie
Internet Systems Consortium, Inc.
950 Charter Street 950 Charter Street
Redwood City, CA 94063 Redwood City, CA 94063
+1 650 423 1301 +1 650 423 1301
vixie@isc.org vixie@isc.org
Akira Kato Akira Kato
University of Tokyo, Information Technology Center University of Tokyo, Information Technology Center
2-11-16 Yayoi Bunkyo 2-11-16 Yayoi Bunkyo
Tokyo 113-8658, JAPAN Tokyo 113-8658, JAPAN
+81 3 5841 2750 +81 3 5841 2750
kato@wide.ad.jp kato@wide.ad.jp
INTERNET-DRAFT August 2006 RESPSIZE
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
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 retain
all their rights. 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
skipping to change at page 12, line 4 skipping to change at page 12, line 36
pertain to the implementation or use of the technology described in this pertain to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or document or the extent to which any license under such rights might or
might not be available; nor does it represent that it has made any might not be available; nor does it represent that it has made any
independent effort to identify any such rights. Information on the independent effort to identify any such rights. Information on the
procedures with respect to rights in RFC documents can be found in BCP procedures with respect to rights in RFC documents can be found in BCP
78 and BCP 79. 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an attempt assurances of licenses to be made available, or the result of an attempt
made to obtain a general license or permission for the use of such made to obtain a general license or permission for the use of such
INTERNET-DRAFT July 2006 RESPSIZE
proprietary rights by implementers or users of this specification can be proprietary rights by implementers or users of this specification can be
obtained from the IETF on-line IPR repository at obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary rights copyrights, patents or patent applications, or other proprietary rights
that may cover technology that may be required to implement this that may cover technology that may be required to implement this
standard. Please address the information to the IETF at standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
 End of changes. 46 change blocks. 
87 lines changed or deleted 135 lines changed or added

This html diff was produced by rfcdiff 1.32. The latest version is available from http://www.levkowetz.com/ietf/tools/rfcdiff/