One document matched: draft-ietf-dnsind-apl-rr-02.txt
Differences from draft-ietf-dnsind-apl-rr-01.txt
INTERNET-DRAFT Peter Koch
Expires: December 1999 Universitaet Bielefeld
Updates: RFC 1035 June 1999
A DNS RR Type for Lists of Address Prefixes (APL RR)
draft-ietf-dnsind-apl-rr-02.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Comments should be sent to the author or the DNSIND WG mailing list
<namedroppers@internic.net>.
Abstract
The Domain Name System is primarily used to translate domain names
into IPv4 addresses using A RRs. Several approaches exist to describe
networks or address ranges. This document specifies a new DNS RR type
"APL" for address prefix lists.
1. Conventions used in this document
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 [RFC2119].
Domain names herein are for explanatory purposes only and should not
be expected to lead to useful information in real life [RFC2606].
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2. Background
The Domain Name System [RFC1034], [RFC1035] provides a mechanism to
assign addresses and other internet infrastructure elements to
hierarchically built domain names. Various types of resource records
have been defined, especially those for IPv4 and IPv6 [RFC1886],
[A6DNSRR] addresses. In [RFC1101] a method is described to publish
information about the address space allocated to an organisation. In
older BIND versions, a weak form of controlling access to zone data
was implemented using TXT RRs describing address ranges.
This document specifies a new RR type for address prefix lists.
3. APL RR Type
An APL record has the DNS type of "APL" [draft: not yet applied for]
and a numeric value of [draft:to be assigned]. The APL RR is defined
in the IN class only. APL RRs cause no additional section processing.
4. APL RDATA format
The RDATA section consists of zero or more strings (<apstring>) of
the form
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| ADDRESSFAMILY |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| PREFIX | N | AFDLENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
/ AFDPART /
| |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
ADDRESSFAMILY 16 bit unsigned value as assigned by IANA
(see IANA Considerations)
PREFIX 8 bit unsigned binary coded prefix length.
Upper and lower bounds and interpretation of
this value are address family specific.
N negation flag, indicates the presence of the
"!" character in the textual format. It has
the value "1" if the "!" was given, "0" else.
AFDLENGTH length in octets of the following address
family dependent part (7 bit unsigned).
AFDPART address family dependent part. See below.
This document defines the AFDPARTs for address families 1 (IPv4) and
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2 (IPv6). Future revisions may deal with additional address
families.
4.1. AFDPART for IPv4
The encoding of an IPv4 address (address family 1) follows the
encoding specified for the A RR by [RFC1035], section 3.4.1. Trailing
zero octets MUST be ignored, regardless of the prefix length.
PREFIX specifies the number of bits of the IPv4 address starting at
the most significant bit. Legal values range from 0 to 32.
An IPv4 AFDPART has a variable length of 0 to 4 octets.
4.2. AFDPART for IPv6
The encoding of an IPv6 address (address family 2) follows the
specification for the AAAA RR in [RFC1886], section 2.2. The 128 bit
address is encoded in network byte order. Trailing zero octets MUST
be ignored, regardless of the prefix length.
PREFIX specifies the number of bits of the IPv6 address starting at
the most significant bit. Legal values range from 0 to 128.
An IPv6 AFDPART has a variable length of 0 to 16 octets.
5. Zone File Syntax
The textual representation of an APL RR in a DNS zone file is as
follows:
<owner> IN <TTL> APL {[!]address/prefix}*
The data consists of zero or more strings of an address, immediately
followed by the "/" character, immediately followed by a decimal
numeric value for the prefix length. Any such string may be preceeded
by a "!" character. The strings are separated by whitespace.
5.1. Textual Representation of IPv4 Addresses
An IPv4 address in the <address> part of an <apstring> is in dotted
quad notation, just as in an A RR. The <prefix> has values from the
interval 0..32 (decimal).
5.2. Textual Representation of IPv6 Addresses
The representation of an IPv6 address in the <address> part of an
<apstring> follows [RFC2373], section 2.2. Legal values for <prefix>
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are from the interval 0..128 (decimal).
6. APL RR usage
An APL RR with empty RDATA is valid and implements an empty list.
Multiple occurences of the same <apstring> in a single APL RR are
allowed and MUST NOT be merged by a DNS server or resolver.
<apstrings> MUST be kept in order and MUST NOT be rearranged or
aggregated.
A single APL RR may contain <apstrings> belonging to different
address families. The maximum number of <apstrings> is upperbounded
by the available RDATA space.
RRSets consisting of more than one APL RR are legal but the
interpretation is left to the particular application. It may choose
to join the lists or treat them as alternatives.
Possible applications include the publication of address ranges
similar to [RFC1101], description of zones built following [RFC2317]
and in-band access control to limit general access or zone transfer
(AXFR) availability for zone data held in DNS servers.
7. Examples
Example usages otlined in the prevois section are shown here. The
line continuation symbol in the second APL RR appears for editorial
purposes only, it is not valid in zone files.
foo.example APL 192.168.32.0/21 !192.168.38.0/28
42.168.192.IN-ADDR.ARPA APL 192.168.42.0/26 192.168.42.64/26 \
192.168.42.128/25
_axfr.sbo.example APL 127.0.0.1/32 172.16.64.0/22
multicast.example APL 224.0.0.0/4 FF00:0:0:0:0:0:0:0/8
Note that since trailing zeroes are ignored in the first APL RR the
AFDLENGTH of both <apstrings> is three.
8. Security Considerations
Any information obtained from the DNS should be regarded as unsafe
unless techniques specified in [RFC2535] or [TSIGRR] were used. The
definition of a new RR type does not introduce security problems into
the DNS, but usage of information made available by APL RRs may
compromise security. This includes disclosure of network topology
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information and in particular the use of APL RRs to construct access
control lists.
9. IANA Considerations
This document does not define any new namespaces. It uses the 16 bit
identifiers for address families maintained by IANA in
ftp://ftp.iana.org/in-notes/iana/assignments/address-family-numbers.
10. Acknowledgements
The author would like to thank Mark Andrews for his review and
constructive comments.
11. References
[A6DNSRR] Crawford,M., Huitema,C., Thomson,S., "DNS Extensions to
Support IPv6 Address Aggregation and Renumbering",
<draft-ietf-ipngwg-dns-lookups-XX.txt>, work in progress
[RFC1034] Mockapetris,P., "Domain Names - Concepts and Facilities",
RFC 1034, STD 13, November 1987
[RFC1035] Mockapetris,P., "Domain Names - Implementation and
Specification", RFC 1035, STD 13, November 1987
[RFC1101] Mockapetris,P., "DNS Encoding of Network Names and Other
Types", RFC 1101, April 1989
[RFC1886] Thomson,S., Huitema.,C., "DNS Extensions to support IP
version 6", RFC 1886, December 1995
[RFC2119] Bradner,S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997
[RFC2181] Elz,R., Bush,R., "Clarifications to the DNS
Specification", RFC 2181, July 1997
[RFC2373] Hinden,R., Deering,S., "IP Version 6 Addressing
Architecture", RFC 2373, July 1998
[RFC2535] Eastlake,D., "Domain Name System Security Extensions", RFC
2535, March 1999
[RFC2606] Eastlake,D., Panitz,A., "Reserved Top Level DNS Names",
RFC 2606, BCP 32, June 1999
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[TSIGRR] Vixie,P., Gudmundsson,O., Eastlake,D., Wellington,B.,
"Secret Key Transaction Signatures for DNS (TSIG)",
<draft-ietf-dnsind-tsig-XX.txt>, work in progress
12. Author's Address
Peter Koch
Universitaet Bielefeld
Technische Fakultaet
Postfach 10 01 31
D-33501 Bielefeld
Germany
+49 521 106 2902
<pk@TechFak.Uni-Bielefeld.DE>
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