Solaris Naming Administration Guide

DNS Text Record Format for XFN References

The Solaris environment conforms to the XFN specification for federating global naming systems within DNS. In order to federate a naming system under DNS, you need to enter information into DNS TXT resource records. This information is then used to construct an XFN reference for that subordinate naming system. This appendix describes the format of these DNS TXT records.

The reference type of an XFN reference is constructed from a TXT record that begins with the XFNREF tag. It has the following format:

TXT "XFNREF rformat reftype"

If spaces occur within the string appearing after TXT, such spaces must be escaped, or the entire string must be enclosed within double quotation marks. The three fields, XFNREF, rformat and reftype, are separated using space (spaces and tabs). rformat specifies format of the reference type identifier. It can be one of the following:

reftype specifies the contents of the reference type identifier.

If no XFNREF TXT record exists, the reference type defaults to an identifier XFN_SERVICE, with an FN_ID_STRING format. If more than one XFNREF TXT record exists, the handling of the record is undefined. The following TXT record is equivalent to the default XFNREF:


The address information for an XFN reference is constructed using TXT records with tags prefixed with the XFN string. Multiple addresses may be specified for a single reference. Records with the same tag are grouped and passed to the handler for each group. Each handler generates zero or more addresses from its group of TXT records and appends the addresses to the reference. The XFNREF tag is special in that it is used only to construct the reference type and thus, it is excluded from the address-construction process.

The syntax of address TXT records is as follows:

XFNaddress_type_tag   address_specific_data

The two fields, XFN_address_type_tag and address_specific_data, are separated using space (spaces and tabs). The address_type_tag specifies the handler to be used for address_specific_data.

TXT records have a limitation of 2K bytes of characters per record. If the address-specific data is too long to be stored in a single TXT record, multiple TXT records may be used, as shown:

TXT "XFNaddress_type_tag address_specific_data1"
TXT "XFNaddress_type_tag address_specific_data2"

When the tag-specific handler is called, both records are passed to it. The handler is responsible for determining the order in which these two lines need to be interpreted.

The order in which TXT records appear is not significant. If lines with different tags are present, lines with the same tag are grouped together before the tag-specific handler is called. In the following example, the handler for tag1 will be called with two text lines, and the handler for tag2 will be called with three text lines.

TXT "XFNtag1 address_specific_data1"
TXT "XFNtag2 address_specific_data2"
TXT "XFNtag1 address_specific_data3"
TXT "XFNtag2 address_specific_data4"
TXT "XFNtag2 address_specific_data5"

Here are some examples of TXT records that can be used for XFN references.

Example 1

TXT		"XFNNISPLUS nismaster"

Example 2

TXT		"XFNDCE (1 fd33328c4-2a4b-11ca-af85-09002b1c89bb...)"

The following is an example of a DNS table with a subordinate naming system bound in it.

@      IN SOA foo          (
             100    ;; Serial
             3600   ;; Refresh
             3600   ;; Retry
             3600   ;; Expire
             3600   ;; Minimum
       NS    nshost
       TXT   "XFNNISPLUS nismaster"
nshost IN  A