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FTSC				FIDONET TECHNICAL STANDARDS COMMITTEE
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Publication:    FTS-5004
Revision:       1 
Title:		DNS Distributed Nodelist
Author(s):	Alexey Vissarionov, 2:5020/545
                FTSC members and administrator
Issue Date:     6 January 2013
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Contents:
0. Introduction
1. Translation of a Fidonet address into a host name
2. Service port location
3. Resolving algorithm
4. NS zone generation
5. Examples
6. References


0. Introduction

Abstract:

This document describes the method of distributing Fidonet nodelist
data through the DNS infrastructure for use by IP-capable Fidonet
mailers.

Status:

This document is a Fidonet Technical Standard (FTS) - it specifies
the best current practices for the Fidonet community. It is hereby
released to the public domain, and may be used, copied or modified
for any purpose whatever.

This document supersedes and replaces FSP-1035.
FSP-1035 is preserved in the FTSC reference library as FRL-1035.


1. Translation of a Fidonet address into a host name.

The format of Fidonet address is:

Z:N/F.P@W

Where the fields are:

Z - Zone Number:
	The zone the node is part of.

N - Net Number:
	The network the node is a member of.

F - Node Number:
	The actual node number.

P - Point Number:
	If the system is a point rather than a node then
	this is their point number at that node.
	Optional. If ".P" is missing then assume 0 (node itself).

W - Network name:
	The name of the "Fidonet Technology Network".
	Optional.

Fidonet address should be translated into host name as:

[pP.]fF.nN.zZ.RD.

where the fields refer to...

P	- Point Number, as in Fidonet address (FA)
	Optional.

F	- Node Number, as in FA
	Must be present.

N	- Net Number, as in FA
	Must be present.

Z	- Zone Number, as in FA
	Must be present.

RD	- Root Domain assigned to DDN.
	Must be present.

In the past, when a node carried IP protocol flags, but no IP
connection information, it was often assumed to partake in the
fidonet.net project and that the information could be found
there. The fidonet.net domain however was lost for the Fidonet
community in 2011 when the keeper allowed it to expire.

Dependence on an individual to maintain the domain registration is
a weakness of the DDN system, therefore it is strongly recommended
that implementations that make use of a DDN service allow the user
to easily configure the root domain and to configure overrides for
often used stationary links so that these links won't be lost when
the DDN service is interrupted or discontinued.

Please note the trailing dot - it should exist in "host name"
parameter when making the DNS query to avoid resolving hosts
like "f545.n5020.z2.ddn.example.tld.office.local. instead of
"f545.n5020.z2.ddn.example.tld."

As points normally don't accept incoming connections, the rest
of this document uses node addresses for any and all examples.
However, the techniques described here may be used for points
as well.


2. Service port location.

If a node accepts connections on a non-standard port, NS zone
should contain a SRV record for every protocol flag.

Format of SRV record is:

_service._proto.name	IN SRV	priority weight port host

Where the fields are:

service:	service name - "binkp" or "ifcico";
		other names may be added in the future
proto:		protocol family - only "tcp" is used for now
name:		record name
priority:	host priority, lower value means more preferred;
		if record contains only one host, this value should
		be set to zero
weight:		relative weight for records with the same priority,
		used for load-balancing; if no load-balancing is
		performed, this value should be set to one
port:		decimal number of the TCP or UDP port
host:		the hostname of the machine providing the service.


3. Resolving algorithm.

* Query DDN for SRV record. If it exists - perform connection using
resolved hostname:port pair.
* Query DDN for AAAA and A records. On success, perform connection
using resolved address and default port.
* If both failed, return the "server not found" error.

Note: CNAME targets MUST NOT be queried for SRV records.


4. NS zone generation.

The only valid source for DDN records is FTS-5000 world nodelist.
Data from partial (network etc.) segments SHOULD NOT appear in
DDN until they get into world nodelist. Data from any sources
other than nodelist MUST NOT appear in DDN NS zones.

To be published in DDN, the node MUST have at least one Internet
address published in the nodelist. The IP protocol flags or the
INA flag SHOULD be used for that purpose, but some nodes use the
system name instead, so the implementations SHOULD look for a
hostname in the protocol flag, the INA flag and the system name
field in that order.

Multiple INA flags MAY be used if they carry different addresses.
Multiple IP protocol flags MAY be used for different port
numbers; if the default port is listed among others, the SRV
record for it MUST be added to resulting NS zone.

If the INA flag (or any of the protocol flags) of any node carries
host name built from the FTN address using DDN or any other method,
that node MUST be skipped and MUST NOT appear in resulting NS zone.
In general, such names SHOULD NOT appear in the nodelist.


5. Examples.

This section contains some examples of valid records which may
appear in DDN.

; INA:fido.example.net,IBN
; no SRV record required
f9999			IN CNAME	fido.example.net.

; INA:192.0.2.123,INA:[2001:0DB8:F1D0::2:5020:9999],IBN
; both A and AAAA records are created
_binkp._tcp.f9999	IN SRV		0 1 24554 f9999
f9999			IN A		192.0.2.123
			IN AAAA		2001:0DB8:F1D0::2:5020:9999

; INA:fido.example.net,IBN:12345
_binkp._tcp.f9999	IN SRV		0 1 12345 fido.example.net.

; INA:192.0.2.123,IBN:12345
_binkp._tcp.f9999	IN SRV		0 1 12345 f9999
f9999			IN A		192.0.2.123

; INA:fido.example.net,IBN,IBN:12345
; here the default port is supported, so we use CNAME to provide
; backward compatibility for old mailers
; also, some sort of (equal) load-balancing is performed here
_binkp._tcp.f9999	IN SRV		0 1 24554 fido.example.net.
			IN SRV		0 1 12345 fido.example.net.
f9999			IN CNAME	fido.example.net.

; IBN:192.0.2.123,IBN:fido.example.net:12345
; only first record (numeric IP) will be available to old mailers
_binkp._tcp.f9999	IN SRV		0 1 12345 fido.example.net.
			IN SRV		0 1 24554 f9999
f9999			IN A		192.0.2.123

; INA:fido.example.net,IBN:fido.example.com,IFC:12345
; both mailers listen at fido.example.net, but only binkp-capable
; mailer listens at fido.example.com
; ifcico-capable mailer uses non-standard port
; also, CNAME record is created to provide backward compatibility
; for old binkp-capable mailers
_binkp._tcp.f9999	IN SRV		0 1 24554 fido.example.net.
			IN SRV		0 1 24554 fido.example.com.
_ifcico._tcp.f9999	IN SRV		0 1 12345 fido.example.net.
f9999			IN CNAME	fido.example.net.

; INA:fido.example.net,IBN,IFC:fido.example.com:12345
; both mailers listen at fido.example.net, but only ifcico-capable
; mailer listens at non-standard port on fido.example.com
_binkp._tcp.f9999	IN SRV		0 1 24554 fido.example.net.
_ifcico._tcp.f9999	IN SRV		0 1 12345 fido.example.com.
			IN SRV		0 1 12345 fido.example.net.
f9999			IN CNAME	fido.example.net.

; IBN:fido.example.net,IFC:fido.example.com:12345
; no INA flag means there's no common address
_binkp._tcp.f9999	IN SRV		0 1 24554 fido.example.net.
_ifcico._tcp.f9999	IN SRV		0 1 12345 fido.example.com.
f9999			IN CNAME	fido.example.net.


6. References.

FTA-1006 "Key words to indicate requirement levels"
FTS-5000 "The Distribution Nodelist"
FTS-5001 "Nodelist flags and userflags"
FTS-1026 "Binkp/1.0 Protocol specification"
FTS-1024 "Raw ifcico mail transfer protocol"
FRL-1035 "DNS Distributed Nodelist".
RFC-2872 "A DNS RR for specifying the location of services (DNS SRV)"


History
=======

   Rev.1, 20130106  - Alexey Vissarionov (2:5020/545), first release.

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