(:redirect DNS/ipv6rDNS:)
Configuring rDNS using NSD
We can configure our rDNS using nsd, an authoritative name server. nsd comes as part of openbsd base so no installation will be necessary.
NOTICE: This guide assumes you have already configured nsd for forward DNS resolution.
IPv6 Subnet
Suppose we have been delegated the rDNS zone for our IPv6 subnet, 2001:550:3402:1:143::/80. To find out our zone, we need to fill in all the missing zeros, put periods between each digit, reverse the digits, then add ip6.arpa:
2001:550:3402:1:143:: # original subnet
2001:0550:3402:0001:0143:: # fill in the missing zeros
2.0.0.1.0.5.5.0.3.4.0.2.0.0.0.1.0.1.4.3 # add periods between each digit
3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2 # reverse the digits
3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa # add ip6.arpa
Here is a simple command to do this:
echo "<IPv6 subnet>"|rev|sed "s/://g;s/\(.\)/\1./g;s/$/ip6.arpa/"
(:if false:)
grep inet6.*48 /etc/hostname.vio0|awk '{print$2}'|rev|sed "s/://g;s/(.)/\1./g;s/$/ip6.arpa/"
(:ifend:)
Replace
For example:
echo "2001:0550:3402:0001"|rev|sed "s/://g;s/\(.\)/\1./g;s/$/ip6.arpa/"
Zone File
Now we must create the zone file in /var/nsd/zones/master/3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa:
$ORIGIN 3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa.
@ 3600 IN SOA ns1.ircnow.org. admin.ircnow.org. (
2021020105 1800 3600 1209600 3600 )
3600 IN NS ns1.jrmu.coconut.ircnow.org.
3600 IN NS ns2.jrmu.coconut.ircnow.org.
0.0.0.0.0.0.0.0.0.0.0.0 3600 IN PTR user1.coconut.ircnow.org.
1.0.0.0.0.0.0.0.0.0.0.0 3600 IN PTR user2.coconut.ircnow.org.
/var/nsd/etc/nsd.conf
Now we only need to add this section to /var/nsd/etc/nsd.conf:
zone:
name: "3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa"
zonefile: "master/3.4.1.0.1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa"
Restart nsd and test
$ doas rcctl restart nsd
We can test using host or [dig: We can test using host or [dig:
host 2001:550:3402:1:143::1 <nameserver-ip>
Replace
You can then test if both forward and reverse DNS lookup work by using netcat to connect to IRC.
(:if false:)
Troubleshooting
Primary and secondary server
If you need a secondary server to host the zone, you can do this as follows. Add to the block that describes your master zone, records about the secondary zone as in the example:
zone:
name: "example.net"
zonefile: "master/example.net"
notify: 20.20.20.20 NOKEY
provide-xfr: 20.20.20.20 NOKEY
Create a new block in the secondary server config file, as in the example:
zone:
name: "example.net"
zonefile: "slave/example.net"
allow-notify: 10.10.10.10 NOKEY
request-xfr: 10.10.10.10 NOKEY
The zone file for NSD
The next step is to write the zone files for NSD. First the forward lookup zone example.net:
; Domain file from My project
example.net. 3600 SOA ns.example.net. admin.example.net. (
2020070701 ; serial YYYYMMDDnn
10800 ; refresh
3600 ; retry
604800 ; expire
86400 ) ; minimum TTL
example.net. NS ns.example.net.
example.net. NS ns.secondary.net.
ns A 10.10.10.10
example.net. A 10.10.10.10
www A 10.10.10.10
irc A 10.10.10.10
imap A 10.10.10.10
smtp A 10.10.10.10
example.net. mx 10 smtp.example.net.
Save this zone file as /var/nsd/zones/master/example.net
Configuration check and start
NSD bring along a tool to check the configuration file before you start or reload the daemon:
$ doas nsd-checkconf /var/nsd/etc/nsd.conf
Any errors are reported, so no news are good news. You can go ahead and start NSD:
$ doas rcctl enable nsd
$ doas rcctl start nsd
If there are issues you can start nsd in debug mode
doas nsd -d -V 3
https://www.denic.de/en/service/tools/nast/
$ORIGIN 1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa.
@ 3600 IN SOA ns1.ircnow.org. admin.ircnow.org. (
2020112906 1800 3600 1209600 3600 )
3600 IN NS cherry.ircnow.org.
3600 IN NS pear.ircnow.org.
3600 IN NS mango.ircnow.org.
3600 IN NS peach.ircnow.org.
3600 IN NS banana.ircnow.org.
3600 IN NS guava.ircnow.org.
3600 IN NS jujube.ircnow.org.
3600 IN NS plum.ircnow.org.
3600 IN NS fig.ircnow.org.
3600 IN NS orange.ircnow.org.
3600 IN NS lemon.ircnow.org.
3600 IN NS grape.ircnow.org.
3600 IN NS coconut.ircnow.org.
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 3600 IN PTR www.example.com.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 3600 IN PTR www.example.org.
In /var/nsd/etc/nsd.conf:
zone:
name: "1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa"
zonefile: "master/1.0.0.0.2.0.4.3.0.5.5.0.1.0.0.2.ip6.arpa"
include-pattern: "ircnow.org"
(:ifend:)