Internet DRAFT - draft-woodworth-bulk-rr
draft-woodworth-bulk-rr
DNSOP Working Group J. Woodworth
Internet-Draft D. Ballew
Updates: 2308, 4033, 4034, 4035 (if CenturyLink, Inc.
approved) S. Bindinganaveli Raghavan
Intended status: Informational Hughes Network Systems
Expires: January 22, 2020 D. Lawrence
Oracle
July 21, 2019
BULK DNS Resource Records
draft-woodworth-bulk-rr-09
Abstract
The BULK DNS resource record type defines a method of pattern-based
creation of DNS resource records based on numeric substrings of query
names. The intent of BULK is to simplify generic assignments in a
memory-efficient way that can be easily shared between the primary
and secondary nameservers for a zone.
Ed note
Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication. This document is
being collaborated on in GitHub at <https://github.com/ioneyez/bulk-
rr>. The most recent version of the document, open issues, etc
should all be available here. The authors gratefully accept pull
requests.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 22, 2020.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Background and Terminology . . . . . . . . . . . . . . . 4
2. The BULK Resource Record . . . . . . . . . . . . . . . . . . 4
2.1. BULK RDATA Wire Format . . . . . . . . . . . . . . . . . 4
2.2. The BULK RR Presentation Format . . . . . . . . . . . . . 6
3. BULK Replacement . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Matching the Domain Name Pattern . . . . . . . . . . . . 7
3.2. Record Generation using Replacement Pattern . . . . . . . 7
3.2.1. Delimiters . . . . . . . . . . . . . . . . . . . . . 8
3.2.2. Delimiter intervals . . . . . . . . . . . . . . . . . 8
3.2.3. Padding length . . . . . . . . . . . . . . . . . . . 9
3.2.4. Final processing . . . . . . . . . . . . . . . . . . 9
4. Known Limitations . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Unsupported Nameservers . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5.1. DNSSEC Signature Strategies . . . . . . . . . . . . . . . 10
5.1.1. On-the-fly Signatures . . . . . . . . . . . . . . . . 10
5.1.2. Alternative Signature Scheme . . . . . . . . . . . . 11
5.1.3. Non-DNSSEC Zone Support Only . . . . . . . . . . . . 11
5.2. DDOS Attack Vectors and Mitigation . . . . . . . . . . . 11
5.3. Implications of Large-Scale DNS Records . . . . . . . . . 11
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. BULK Examples . . . . . . . . . . . . . . . . . . . 14
A.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 14
A.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 14
A.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 15
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A.4. Example 4 . . . . . . . . . . . . . . . . . . . . . . . . 15
A.5. Example 5 . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The BULK DNS resource record defines a pattern-based method for on-
the-fly resource record generation. It is essentially an enhanced
wildcard mechanism, constraining generated resource record owner
names to those that match a pattern of variable numeric substrings.
It is also akin to the $GENERATE master file directive [bind-arm]
without being limited to numeric values and without creating all
possible records in the zone data.
For example, consider the following record:
example.com. 86400 IN BULK A (
pool-A-[0-255]-[0-255].example.com.
10.55.${1}.${2}
)
It will answer requests for pool-A-0-0.example.com through pool-
A-255-255.example.com with the IPv4 addresses 10.55.0.0 through
10.55.255.255.
Much larger record sets can be defined while minimizing the
associated requirements for server memory and zone transfer network
bandwidth.
This record addresses a number of real-world operational problems
that authoritative DNS service providers experience. For example,
operators who host many large reverse lookup zones, even for only
IPv4 space in in-addr.arpa, would benefit from the disk space, memory
size, and zone transfer efficiencies that are gained by encapsulating
a simple record-generating algorithm versus enumerating all of the
individual records to cover the same space.
Production zones of tens of thousands of pattern-generated records
currently exist, that could be reduced to just one BULK RR. These
zones can look deceptively small on the primary nameserver and
balloon to 100MB or more when expanded,
BULK also allows administrators to more easily deal with singletons,
records in the pattern space that are an exception to the normal data
generation rules. Whereas a mechanism like $GENERATE may need to be
adjusted to account for these individual records, the processing
rules for BULK have explicit records more naturally override the
dynamically generated ones. This collision problem is not just a
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theoretical concern, but a real source of support calls for
providers.
Pattern-generated records are also not only for the reverse DNS
space. Forward zones also occasionally have entries that follow
patterns that would be well-addressed by the BULK RR.
1.1. Background and Terminology
The reader is assumed to be familiar with the basic DNS and DNSSEC
concepts described in [RFC1034], [RFC1035], [RFC4033], [RFC4034], and
[RFC4035]; subsequent RFCs that update them in [RFC2181] and
[RFC2308]; and DNS terms in [RFC7719].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when, and only when, they appear in all capitals, as shown
here.
2. The BULK Resource Record
The BULK resource record enables an authoritative nameserver to
generate RRs for other types based upon the query received.
The Type value for the BULK RR type is TBD.
The BULK RR is class-independent.
2.1. BULK RDATA Wire Format
The RDATA for a BULK RR is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Match Type | /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Domain Name Pattern /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ Replacement Pattern /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Match Type identifies the type of the RRset to be generated by this
BULK record. It is two octets corresponding to an RR TYPE code as
specified in [RFC1035], Section 3.2.1.
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Domain Name Pattern consists of a pattern encoded as a wire-format
fully qualified domain name. The full name is used so that numeric
substrings above the zone cut can be captured in addition to those in
the zone. It needs no length indicator for the entire field because
the root label marks its end.
Special characters are interpreted as per the following Augmented
Backus-Naur Form (ABNF) notation from [RFC5234].
match = 1*(range / string)
range = "[" [decnum "-" decnum] "]" /
"<" [hexnum "-" hexnum] ">"
; create references for substitution
; limit of 32 references
; [] is syntactic sugar for 0-255
; <> is syntactic sugar for 00-ff
string = 1*(ctext / quoted-char)
decnum = 1*decdigit
; constrained to 65535 maximum.
hexnum = 1*hexdigit
; constrained to ffff maximum.
octet = %x00-FF
decdigit = %x30-39
; 0-9
hexdigit = decdigit / 0x41-0x46 / 0x61-66
; 0-9, A-F, a-f
ctext = <any octet excepting "\">
quoted-char = "\" octet
; to allow special characters as literals
Interpretation of the Domain Name Pattern is described in detail in
the "BULK Replacement" section. Note that quoted-char must be stored
in the wire format to preserve its semantics when the BULK RR is
interpreted by nameservers.
The limit of 32 references is meant to simplify implementation
details. It is largely but not entirely arbitrary, as it could
capture every individual character of the text representation of a
full IPv6 address.
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Replacement Pattern describes how the answer RRset MUST be generated
for the matching query. It needs no length indicator because its end
can be derived from the RDATA length minus Match Type and Domain Name
Pattern lengths. It uses the following additional ABNF elements:
replace = 1*(reference / string)
reference = "$" "{" (positions / "*") [options] "}"
positions = (position / posrange) 0*("," (position / posrange))
posrange = position "-" position
position = 1*decnum
options = delimiter [interval [padding]]
delimiter = "|" 0*(ctext | quoted-char)
; "\|" to use "|" as delimiter
; "\\" to use "\" as delimiter
interval = "|" *2decdigit
padding = "|" *2decdigit
[ Is the formatting complexity beyond simple ${1}, ${2}, etc, really
worth it? I definitely see how it could make for shorter replacement
patterns, but does it enhance their clarity and usability, adding a
feature someone really wants? ]
The Replacement Pattern MUST end in the root label if it is intended
to represent a fully qualified domain name.
2.2. The BULK RR Presentation Format
Match Type is represented as an RR type mnemonic or with [RFC3597]'s
generic TYPE mechanism.
Domain Name Pattern is represented as a fully qualified domain name
as per [RFC1035] Section 5.1 rules for encoding whitespace and other
special characters.
Replacement Pattern is represented by the standard <character-string>
text rules for master files as per [RFC1035] section 5.1.
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It is suggested that lines longer than 80 characters be wrapped with
parenthetical line continuation, per [RFC1035] Section 5.1, starting
after Match Type and ending after Replacement Pattern.
3. BULK Replacement
When a BULK-aware authoritative nameserver receives a query for which
it does not have a matching name or a covering wildcard, it MUST then
look for BULK RRs at the zone apex, selecting all BULK RRs with a
Match Type that matches the query type and a Domain Name Pattern that
matches the query name. Note that query type ANY will select all
Match Types, and all query types match a CNAME or DNAME Match Type.
One or more answer RRs will be generated per the replacement rules
below. Examples are provided in an appendix.
By only triggering the BULK algorithm when the query name does not
exist, administrators are given the flexibility to explicitly
override the behaviour of specific names that would otherwise match
the BULK record's Domain Name Pattern. This is unlike BIND's
$GENERATE directive, which adds the generated RRs to any existing
names.
3.1. Matching the Domain Name Pattern
A query name matches the Domain Name Pattern if the characters that
appear outside the numeric ranges match exactly and those within
numeric ranges have values that fall within the range. Numeric
matches MUST be of the appropriate decimal or hexadecimal type as
specified by the delimiters in the pattern. For example, if a range
is given as [0-255], then FF does not match even though its value as
a hexadecimal number is within the range. Leading zeros in the
numeric part(s) of the qname MUST be ignored; for example,
001.example.com, 01.example.com and 1.example.com would all match
[].example.com.
When a query name matches a Domain Name Pattern, the value in each
numeric range is stored for use by the Replacement Pattern, with
reference numbers starting at 1 and counting from the left. For
example, matching the query name host-24-156 against
host-[0-255]-[0-255] assigns 24 to ${1} and 156 to ${2}.
3.2. Record Generation using Replacement Pattern
The Replacement Pattern generates the record data by replacing the
${...} references with data captured from the query name, and copying
all other characters literally.
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The simplest form of reference uses only the reference number between
the braces, "{" and "}". The value of the reference is simply copied
directly from the matching position of the query name.
The next form of reference notation uses the asterisk, "*". With
${*}, all captured values in order of ascending position, delimited
by its default delimiter (described below), are placed in the answer.
The commercial-at, "@" symbol captures in the same way only in order
of descending position.
Numeric range references, such as ${1-4}, replaces all values
captured by those references, in order, delimited by the default
delimiter described below. To reverse the order in which they are
copied, reverse the upper and lower values, such as ${4-1}. This is
useful for generating PTR records from query names in which the
address is encoded in network order.
Similar to range references, separating positions by commas creates
sets for replacement. For example, ${1,4} would be replaced by the
first and fourth captured values, delimited its default delimiter.
This notation may be combined with the numeric range form, such as
${3,2,1,8-4}.
3.2.1. Delimiters
A reference can specify a delimiter to use by following a vertical
bar, "|", with zero or more characters. Zero characters, such as in
${1-3|}, means no delimiter is used, while other characters up to an
unescaped vertical bar or closing brace are copied between position
values in the replacement. The default delimiter is the hyphen, "-".
3.2.2. Delimiter intervals
A second vertical bar in the reference options introduces a delimiter
interval. The default behavior of a multi-position reference is to
combine each captured value specified with a delimiter between each.
With a delimiter interval the delimiters are only added between every
Nth value. For example, ${*|-|4} adds a hyphen between every group
of four captured positions. This can be a handy feature in the IPv6
reverse namespace where every nibble is captured as a separate value
and generated hostnames include sets of 4 nibbles. An empty or 0
value for the delimiter interval MUST be interpreted as the default
value of 1.
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3.2.3. Padding length
The fourth and final reference option determines the field width of
the copied value. Shorter values MUST be padded with leading zeroes
("0") and longer values MUST be truncated to the width.
The default behavior, and that of an explicit empty padding length,
is that the captured query name substring is copied exactly. A width
of zero "0" is a signal to "unpad", and any leading zeros MUST be
removed. [ Unnecessary complexity? ]
If a delimiter interval greater than 1 is used, captured values
between the intervals will be concatenated and the padding or
unpadding applied as a unit and not individually. An example of this
would be ${*||4|4} which would combine each range of 4 captured
values and pad or truncate them to a width of 4 characters.
[ If this is kept, the element/feature should probably be renamed
from "padding" since it is just as likely to truncate. ]
3.2.4. Final processing
The string that results from all replacements is converted to the
appropriate RDATA format for the record type. If the conversion
fails, the SERVFAIL rcode MUST be set on the response, representing a
misconfiguration that the server was unable to perform. [ The EDNS
extended-error code would be useful here. ]
The TTL of each RR generated by a BULK RR is the TTL of the
corresponding BULK record itself. [ BULK should probably have its
own TTL field because using that of the record itself feels like bad
design. On the other hand, if BULK is never meant to be queried for
directly and only appears in authoritative data, its own TTL is
pretty useless normally. ]
The class for the RRSet is the class of the BULK RR.
If the generated record type is one that uses domain names in its
resource record data, such as CNAME, a relative domain names MUST be
fully qualified with the origin domain of the BULK RR.
4. Known Limitations
This section defines known limitations of the BULK resource type.
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4.1. Unsupported Nameservers
Authoritative nameservers that do not understand the semantics of the
new record type will not be able to deliver the intended answers even
when the type appears in their zone data This significantly affects
the interoperability of primary versus secondary authorities that are
not all running the same software. Adding new RRs which affect
handling by authoritative servers, or being unable to add them, is an
issue that needs to be explored more thoroughly within dnsop.
5. Security Considerations
Two known security considerations exist for the BULK resource record,
DNSSEC and DDOS attack vectors.
5.1. DNSSEC Signature Strategies
DNSSEC was designed to provide validation for DNS resource records,
requiring each tuple of owner, class, and type to have its own
signature. This essentially defeats the purpose of providing large
generated blocks of RRs in a single RR as each generated RR would
require its own legitimate RRSIG record.
In the following sections several options are discussed to address
this issue. Of the options, on-the-fly provides the most secure
solution and NPN [npn-draft] provides the most flexible.
5.1.1. On-the-fly Signatures
A significant design goal of DNSSEC was to be able to do offline
cryptographic signing of zone contents, keeping the key material more
secure.
On-the-fly processing requires authoritative nameservers to sign
generated records as they are created. Not all authoritative
nameserver implementations offer on-the-fly signatures, and even with
those that do not all operators will want to keep signing keys
online. This solution would either require all implementations to
support on-the-fly signing or be ignored by implementations which can
not or will not comply.
One possibly mitigation for addressing the risk of keeping the zone
signing key online would be to continue to keep the key for signing
positive answers offline and introduce a second key for online
signing of negative answers.
No changes to validating resolvers is required to support this
solution.
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5.1.2. Alternative Signature Scheme
Previous versions of this draft proposed a new signature scheme using
a Numeric Pattern Normalization (NPN) RR. It was a method to support
offline signatures for BULK records, with the drawback that is
required updates to DNSSEC-aware resolvers.
That mechanism is not specific to BULK and has been removed from the
current draft. If there is further interest in pursuing it, it can
be reopened as a separate draft.
5.1.3. Non-DNSSEC Zone Support Only
As a final option zones which wish to remain entirely without DNSSEC
support may serve such zones without either of the above solutions
and records generated based on BULK RRs will require zero support
from recursive resolvers.
5.2. DDOS Attack Vectors and Mitigation
As an additional defense against Distributed Denial Of Service (DDOS)
attacks against recursive (resolving) nameservers it is highly
recommended shorter TTLs be used for BULK RRs than others. While
disabling caching with a zero TTL is not recommended, as this would
only result in a shift of the attack target, a balance will need to
be found. While this document uses 24 hours (86400 seconds) in its
examples, values between 300 to 900 seconds are likely more
appropriate and is RECOMMENDED. What is ultimately deemed
appropriate may differ from zone to zone and administrator to
administrator.
[ I am unclear how this helps DDOS mitigation against anyone at all,
and suspect this section should be removed.. ]
5.3. Implications of Large-Scale DNS Records
The production of such large-scale records in the wild may have some
unintended side-effects. These side-effects could be of concern or
add unexpected complications to DNS based security offerings or
forensic and anti-spam measures. While outside the scope of this
document, implementers of technology relying on DNS resource records
for critical decision making must take into consideration how the
existence of such a volume of records might impact their technology.
Solutions to the magnitude problem for BULK generated RRs are
expected be similar if not identical to that of existing wildcard
records, the core difference being the resultant RDATA will be unique
for each requested Domain Name within its scope.
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The authors of this document are confident that by careful
consideration, negative_side-effects produced by implementing the
features described in this document can be eliminated from any such
service or product.
6. Privacy Considerations
The BULK record does not introduce any new privacy concerns to DNS
data.
7. IANA Considerations
IANA is requested to assign numbers for the BULK RR.
8. Acknowledgments
This document was created as an extension to the DNS infrastructure.
As such, many people over the years have contributed to its creation
and the authors are appreciative to each of them even if not thanked
or identified individually.
A special thanks is extended for the kindness, wisdom and technical
advice of Robert Whelton (CenturyLink, Inc.) and Gary O'Brien
(Secure64 Software Corp).
9. References
9.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/info/rfc2181>.
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[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
<https://www.rfc-editor.org/info/rfc2308>.
[RFC2317] Eidnes, H., de Groot, G., and P. Vixie, "Classless IN-
ADDR.ARPA delegation", BCP 20, RFC 2317,
DOI 10.17487/RFC2317, March 1998,
<https://www.rfc-editor.org/info/rfc2317>.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
2003, <https://www.rfc-editor.org/info/rfc3597>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
9.2. Informative References
[bind-arm]
Internet Systems Consortium, "BIND 9 Configuration
Reference", 2016,
<https://ftp.isc.org/isc/bind9/cur/9.9/doc/arm/
Bv9ARM.html>.
[npn-draft]
Internet Systems Consortium, "Numeric Pattern
Normalization (NPN)", 2019,
<https://github.com/ioneyez/npn>.
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[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.
Appendix A. BULK Examples
A.1. Example 1
$ORIGIN 2.10.in-addr.arpa.
@ 86400 IN BULK PTR (
[0-255].[0-255].[0-255].[0-255].in-addr.arpa.
pool-${4-1}.example.com.
)
A query received for the PTR of 4.3.2.10.in-addr.arpa will create the
references ${1} through ${4} with the first four labels of the query
name. The ${4-1} reference in the replacement pattern will then
substitute them in reverse with the default delimiter of hyphen
between every character and no special field width modifications.
The TTL of the BULK RR is used for the generated record, making the
response:
4.3.2.10.in-addr.arpa 86400 IN PTR pool-10-2-3-4.example.com.
A.2. Example 2
$ORIGIN 2.10.in-addr.arpa.
@ 86400 IN BULK PTR (
[0-255].[0-255].[0-255].[0-255].in-addr.arpa.
pool-${2,1|||3}.example.com.
)
Example 2 is similar to Example 1, except that it modifies the
replacement pattern. The empty option after the first vertical bar
causes no delimiters to be inserted, while the second empty option
that would keep the delimiter interval as 1. The latter is relevant
because the final value, padding of 3, is applied over each delimiter
interval even when no delimiter is used. Not all captures from the
substring are required to be used in the response.
The result is that a query for the PTR of 4.3.2.10.in-addr.arpa
generates this response:
4.3.2.10.in-addr.arpa 86400 IN PTR pool-003004.example.com.
[ Admittedly you can't do this very effectively without the field
width complexity. Is this sort of name common? Does it need
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support? Admittedly $GENERATE had the feature, but is that reason
enough? ]
[ Change this to a hex matching example? ]
A.3. Example 3
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
@ 86400 IN BULK PTR (
<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>.<>
poolAA-${16-8|-|4}.example.com.
)
This example introduces IPv6 where 16 individual nibbles are captured
and the last 8 are combined into 2 blocks of 4, separated by a
hyphen.
A query for the IP of 2001:db8::dead:beef results in a PTR RR with
the value of poolAA-dead-beef.example.com.
A.4. Example 4
$ORIGIN example.com.
@ 86400 IN BULK AAAA (
poolAA-<0-ffff>-<0-ffff>.example.com.
${@|.|1}.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
)
This example performs the reverse of example 3, where a query of
poolAA-dead-beef.example.com captures "dead" and "beef", reversing
the nibbles and using a dot (.) as the delimiter to form a valid AAAA
record.
A.5. Example 5
This example contains a classless IPv4 delegation on the /22 CIDR
boundary as defined by [RFC2317]. The network for this example is
"10.2.0/22" delegated to a nameserver "ns1.sub.example.com.". RRs
for this example are defined as:
$ORIGIN 2.10.in-addr.arpa.
@ 7200 IN BULK CNAME [0-255].[0-3] ${*|.}.0-3
0-3 86400 IN NS ns1.sub.example.com.
A query for the PTR of 25.2.2.10.in-addr.arpa is received and the
BULK record with the CNAME Match Type matches all query types. 25
and 2 are captured as references, and joined in the answer by the
period (".") character as a delimiter, with ".0-3" then appended
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literally and fully qualified by the origin domain. The final
synthesized record is:
25.2.2.10.in-addr.arpa 7200 IN CNAME 25.2.0-3.2.10.in-addr.arpa.
[ Without $* and options complexity, the pattern to get the same
result is just ${1}.{$2}.0-3 which is not really significantly
onerous to enter, and slightly less arcane looking to comprehend. ]
Authors' Addresses
John Woodworth
CenturyLink, Inc.
4250 N Fairfax Dr
Arlington VA 22203
USA
Email: John.Woodworth@CenturyLink.com
Dean Ballew
CenturyLink, Inc.
2355 Dulles Corner Blvd, Ste 200 300
Herndon VA 20171
USA
Email: Dean.Ballew@CenturyLink.com
Shashwath Bindinganaveli Raghavan
Hughes Network Systems
11717 Exploration Lane
Germantown MD 20876
USA
Email: shashwath.bindinganaveliraghavan@hughes.com
David C Lawrence
Oracle
Email: tale@dd.org
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