A Bourne again shell (bash) script to create bind reverse IPv6 zone data. RFC 1034 Sect 5.2.1.2 specifies the forward and reverse zone file formats, with the reversed format as a reversed dotted format, for example:
4.3.2.1.IN-ADDR.ARPA IN PTR host.example.com.
Given the standard above, the reverse file for IPv6 becomes rather challenging. For example, the IPv6 address for host.example.com may be 2001:db8:a1ea:cafe::2048 The reverse record would be:
8.4.0.2.0.0.0.0.0.0.0.0.0.0.0.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR host.example.com.
As you can see this is not a transformation you want to do by hand more than once.
Reverse zone files are very useful when using tools such as tcpdump or wireshark, as they will do a reverse DNS lookup (based on the IP address), and provide host name information in the packet capture, making it easier to determine traffic conversations.
The script is written in bash shell, so that it can run on small embedded systems, such as my OpenWrt router which is running bind.
The script does not create an entire reverse zone file. The top portion will be configured for you DNS server, and this script does not try to replace or understand that configuration.
The script does read the forward file and parses out the following:
- The ORIGIN to obtain the domain name (part of the Fully Qualified Domain Name, FQDN)
- The AAAA records which are parsed into IPv6 address and host names
Bash is terrible at string handling, why write this script in bash? Because I wanted it to run on my router (OpenWRT), and just about every where else, with the minimal amount of dependencies. It is possible to run Python on OpenWRT, but Python requires more storage (more packages) than just bash.
Help
$ ./6rev_zone_creator.sh -h
./6rev_zone_creator.sh - IPv6 Reverse DNS Zone Creator for BIND
e.g. ./6rev_zone_creator.sh -f <zonefile>
-f <zonefile>
By Craig Miller - Version: 0.93
Generating reverse zone data:
$ ./6rev_zone_creator.sh -f /tmp/example.com.zone
7.1.1.a.3.d.e.f.f.f.d.1.4.2.2.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6obake.example.com.
4.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6ha.example.com.
a.1.f.0.e.c.e.f.f.f.4.2.1.1.2.0.0.1.0.0.d.b.b.e.0.7.4.0.1.0.0.2.ip6.arpa. IN PTR 6maile.example.com.
3.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.d.b.b.e.0.7.4.0.1.0.0.2.ip6.arpa. IN PTR 6palapala.example.com.
8.c.b.d.1.e.e.f.f.f.4.2.1.1.2.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6halaconia.example.com.
7.7.1.8.e.a.e.f.f.f.d.d.a.9.2.1.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6kukuilani.example.com.
3.4.c.3.f.1.8.6.4.e.a.7.4.8.d.2.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6koamx.example.com.
...
a.7.4.2.9.f.b.a.1.1.d.b.0.6.3.7.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6eono.example.com.
e.f.2.6.0.8.e.f.f.f.7.2.0.0.a.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6devuan.example.com.
a.f.e.4.a.e.e.f.f.f.7.2.0.0.a.0.e.f.a.c.a.e.1.a.8.b.d.0.1.0.0.2.ip6.arpa. IN PTR 6alpine.example.com.
;Pau
The script is dependent on bash for array support, and grep, both of which should be readily available on any linux distro.
Additionally, it relies on expand6.sh available on github.com/cvmiller/expand6
All code by Craig Miller cvmiller at gmail dot com. But ideas, and ports to other languages are welcome.
This project is open source, under the GPLv2 license (see LICENSE)