gen6dns -- A command to manage DNS names for IPv6 hosts
=======================================================

(c) Feb 2015 - Nov 2015  H. Zuleger HZNET

This version of gen6dns is based on a previous one which uses a
different file format, so both versions are not compatible to each other.

## Overview

The command uses a text file as input "database". Each line represents
a single interface of an host which should get a name in the domain name system.

In it's simplest form, a line contains a dns name (label) for an IP interface.
Because of the fact that most of the hosts are single homed, each line
represents a host via its interface.

The next column in the line is the MAC address of the interface written in
the typical way, which means 6 times two hex digits separated by ":" or "-",
or 3 times four hex digits separated by ".".
In this case a 64 bit eui-64 interface identifier will be constructed out of
the MAC address.
If the column starts with two double colons ("::"), than these are the right
64 bit of the IPv6 address, so it is the Interface IDentifier (IID) itself.

The next column is the subnet identifier written as a four digit hex value enclosed
in double colons.


## Example

Example (hosts.simple):

	horst		00:17:53:85:80:3b	:c1:
	gustav.test	0013.35a2.91f5		:2:
	hugo <2h>	::d9b2:56f3:7694:1c5c	:c1:
	rtr1		::a:1			:0:

The name can be a domain name followed by an TTL value enclosed in "<>".

The command

	$ gen6dns -f -S -p 2001:db8:ab::/48  hosts.simple
	horst                		IN  AAAA	2001:db8:ab:c1:217:53ff:fe85:803b
	gustav.test          		IN  AAAA	2001:db8:ab:2:213:35ff:fea2:91f5
	hugo                 	   7200	IN  AAAA	2001:db8:ab:c1:d9b2:56f3:7694:1c5c
	rtr1                 		IN  AAAA	2001:db8:ab::a:1

generates the forward dns entries for the given prefix.
The output can be redirected into a file to include it for example in a BIND zone file.
The option `-S` shortens the IPv6 address in the usual way.

The corresponding reverse entries are generated with a second run.  Now the option
`-o <domain>` is needed to define the target FQDN of the PTR record.

	$ gen6dns -r -o example.net  -p 2001:db8:ab::/48  hosts.simple
	b.3.0.8.5.8.e.f.f.f.3.5.7.1.2.0.1.c.0.0          IN  PTR	horst.example.net.
	5.f.1.9.2.a.e.f.f.f.5.3.3.1.2.0.2.0.0.0          IN  PTR	gustav.test.example.net.
	c.5.c.1.4.9.6.7.3.f.6.5.2.b.9.d.1.c.0.0     7200 IN  PTR	hugo.example.net.
	1.0.0.0.a.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0          IN  PTR	rtr1.example.net.

In this example the reverse entry is split at the /48 boundary, so all PTR records
end up in one reverse zone.


## Subnet name definition

Instead of the subnet ID, a subnet name can be used if a mapping between subnet name
and ID is done before.
To start a subnet definition put the text `%%SUBNET SECTION` into a file, and
then define all your subnets with lines containing a subnet name followed by a subnet ID
given in the same way as in the host file.

	%%SUBNET SECTION

	#name	subnetid
	clt	:c1:
	srv	:2:
	lo	:0:

Lines starting with a hash (`#`) are comment lines.
The comment char can be changed by using the option `-C '<char>'`.
By the way: all columns are delimited by white space characters. If someone
wants to change this, option `-D '<delimchar>'` can be used for.
Reading the above subnet mapping in before the hosts file, the subnet name
can be used instead of the subnet id itself:

	horst		00:17:53:85:80:3b	clt
	gustav.test	0013.35a2.91f5		srv
	hugo <2h>	::d9b2:56f3:7694:1c5c	clt
	rtr1		::a:1			lo


## Writing into files

Instead of printing the records to stdout, if gen6dns is run with option `-w` the
dns records will be writen into files.
The name of the file with the forward resource records is g6d.<domain>, while
the name of the file with the reverse records is g6r.<subnetid>.
If the option `-w`is used to write the output into files, the split of the
reverse records can be done on any nibble boundary down to a /64.

	$ gen6dns -w -b 64 -o example.net -S -p 2001:db8:ab::/48  subnet.txt hosts.txt

Now four files are created:

	$ ls g6*
	g6d.example.net.
	g6r.0000
	g6r.0002
	g6r.00c1

One file for the AAAA records, and one file per subnet for the PTR records.


## More than one prefix

Option `-p <prefix>` defines the network prefix used to generate the full IPv6 address.
IPv6 is well defined to work with multiple IPv6 addresses per interface.  In this case a
DNS entry for a host has two or more AAAA records, one for each prefix.
While from the protocol point of view not required, the use of the same subnet and
interface ID for each prefix is highly recommended.

To use more then one prefix, just add another -p option to the gen6dns run.
The forward file will then contain one AAAA record per prefix.
The reverse file can be used for all delegated prefix zones thanks to the use of
the same subnetid.


## Views or Subdomains

DNS can use so called "views" to manage different answers depending on who is asking.
In this case different zone files for the same zone are needed.
This feature is mainly used to "hide" some of the hosts from outside dns resolution.

To handle this, two zone files must be provided, and for each host the scope must be
defined.

Another way to achive this is to use different domains or subdomains for internal
and external use.

In general the use of subdomains should be preferred, because views have some problems
with DNSSEC.
However both mechanism are supported by `gen6dns` via scope definitions.

A SCOPE SECTION is used to define a name, optional a name for a view, a domain name
and a matching prefix:

	%%SCOPE SECTION
	#name		view	domain			matchprefix
	pub		*	example.de.		2000::/3	# match on any public prefix
	ula		intern	int.example.de.		fc00::/7	# match on ULA prefixes

Both, the name of the view and the domain name is used to set up the output filename
if option -w is used.
The filename is `g6d_<viewname>.>domain>` for a forward zone and `g6r_<viename>.<subnetid>`
for the reverse zone.

To define which host gets which DNS record, each host entry can be extended by a scopelist
enclosed in brackets.

	# label		mac_address/IID		subnet_id
	horst		00:17:53:85:80:3b	clt	[pub,ula]
	gustav.test	0013.35a2.91f5		srv	[pub]
	hugo <2h>	::d9b2:56f3:7694:1c5c	clt	[pub,ula]
	rtr1		::a:1			lo	[ula]

	$ gen6dns -w -p 2001:db8:ab::/48 -p fdb7:5796:cded::/48  scope.txt subnet.txt hosts.txt
	$ ls g6*
	g6d.example.de.
	g6d_intern.int.example.de.
	g6r.0
	g6r_intern.0

	$ cat g6d.example.de.
	horst                	IN  AAAA	2001:0db8:00ab:00c1:0217:53ff:fe85:803b
	gustav.test          	IN  AAAA	2001:0db8:00ab:0002:0213:35ff:fea2:91f5
	hugo             7200	IN  AAAA	2001:0db8:00ab:00c1:d9b2:56f3:7694:1c5c

	$ cat g6d_intern.int.example.de.
	horst                	IN  AAAA	fdb7:5796:cded:00c1:0217:53ff:fe85:803b
	hugo             7200	IN  AAAA	fdb7:5796:cded:00c1:d9b2:56f3:7694:1c5c
	rtr1                 	IN  AAAA	fdb7:5796:cded:0000:0000:0000:000a:0001

	$ cat g6r.0
	b.3.0.8.5.8.e.f.f.f.3.5.7.1.2.0.1.c.0.0          IN  PTR	horst.example.de.
	5.f.1.9.2.a.e.f.f.f.5.3.3.1.2.0.2.0.0.0          IN  PTR	gustav.test.example.de.
	c.5.c.1.4.9.6.7.3.f.6.5.2.b.9.d.1.c.0.0     7200 IN  PTR	hugo.example.de.

	$ cat g6r_intern.0
	b.3.0.8.5.8.e.f.f.f.3.5.7.1.2.0.1.c.0.0          IN  PTR	horst.int.example.de.
	c.5.c.1.4.9.6.7.3.f.6.5.2.b.9.d.1.c.0.0     7200 IN  PTR	hugo.int.example.de.
	1.0.0.0.a.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0          IN  PTR	rtr1.int.example.de.