Experimental RRs


Because DNS is ubiquitous, it is a handy mechanism for many things. Experimental RRs represent suggested uses of DNS, and might make it as an Internet standard in the future. If more appropriate or elegant ways to implement the given mechanisms are developed, they will probably be preferred to the existing RRs.

AFSDB (AFS Database Location)

Defined in RFC 1183:

 domainname     AFSDB subtype# host 

The AFSDB record is used for cross-site AFS and DCE/NCA network filesystem mounting. Subtype 1 is used for AFS, and subtype 2 is used for DCE. If you use the AFS or DCE filesystem, the AFSDB record is documented in the accompanying documents.

ISDN

Defined in RFC 1183, section 3.2:

 domainname     ISDN ISDN-address# sub-address# 

This RR defines a telephone number and was meant to be used in connection with the X25 record for WAN routing over ISDN/X25 circuits. See the description of the X25 record for more information.

KEY (Public Key)

Defined in RFC 2065.

See the SIG record type.

LOC (Location)

Defined in RFC 1876.

This record is meant to provide DNS with the tool to replace UUCP maps. The LOC record holds a geographical position in latitude, longitude, and altitude, as well as the size of the named entity. The sole use of this record is to draw maps. It would, if employed, enable automatic tools to draw geographically as well as topologically correct maps. I believe that GPS receivers must be more widespread before this record sees wide employment. See also the GPOS record type.

Another proposed name for this record type was ICBM, because of the ease with which high-precision LOC records can be used to automate strategic nuclear attacks.

KX (Key Exchange)

Defined in RFC 2230:

 domainname     KX preference# host 

This record defines a key server to be used with IPSEC. It is designed to be used with only DNS-SEC. Otherwise, no chain of trust exists to ensure the authenticity of the retrieved KX record, which would make the information worthless at least in a security context. The preference field has the same meaning as in the MX record. In addition, the host field must be a hostname that refers to a CNAME, A, or AAAA record.

NULL

Defined in RFC 1035, section 3.3.10.

NULL records are not allowed in zone files, so just forget about them. A NULL record can contain up to 65,536 octets of anything, or nothing.

NAPTR (Name Authority Pointer)

Defined in RFC 2168.

The fact that URLs are not time-resistant is something most of us know only too well. This RFC defines a scheme to resolve URNs, which are similar to URLs but can resist time, in theory. These, combined with SRV records, are part of the framework that will help keep URNs (if they come into use) time resistant.

NXT (Next Valid Name)

Defined in RFC 2065.

See the SIG record type.

SIG (Signature)

Defined in RFC 2065.

Realizing how important and unprotected DNS and the data in DNS is, RFC 2065 suggests security mechanisms for DNS, called DNS-SEC. DNS-SEC defines the facilities necessary to authenticate retrieved data and to verify that DNS answers have not been altered in transit. Implementation of this is being worked on in BIND 9, and it could be the beginning of the end of the security problems DNS has if it becomes widely implemented and employed.

The SIG record provides a crypto signature for each record in a zone. The NXT record would then provide the name of the next record in the zone. By traversing the zone using the NXT records, each signed, you can verify the non-existence of a name in a zone. This provides a secure, authenticated way to retrieve RRs as well as find out that a hostname does not exist in a zone, which are equally significant tasks.

SINK (The Kitchen Sink Record)

Defined in http://www.ietf.org/internet-drafts/draft-ietf-dnsind-kitchen-sink-02.txt, which expired in March 2000.

This proposed record specifically enables databases/structured storage (mis)using DNS. The TXT record has been suggested for general storage many times, but the proposals have all disappeared without a trace. Time will tell how the SINK RR fares.



The Concise Guide to DNS and BIND
The Concise Guide to DNS and BIND
ISBN: 0789722739
EAN: 2147483647
Year: 1999
Pages: 183

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