Having MaraDNS be a master DNS server
A master (sometimes called primary) DNS server is a DNS server
that other DNS servers can automatically transfer zone files
from. There are limitations to this way of transferring zone
files; zone files transferred this way lose all comments and the
ordering of records in the zone file is usually changed.
In other words, DNS has a mechanism for automatically having
multiple different servers have the same zone file data. This is
akin to the rsync program; this allows one to change a zone file
on the master machine, then have the slave machines
automatically transfer the zone file from the master machine.
This is useful when one wants to have multiple machines serving
DNS data. This is also useful when one wants to register a
domain, but only has a single IP on the internet. There are a
number of free DNS secondary (slave) services out there that one
can use to have a second IP for a DNS server of a domain.
To set this up, one needs to run the zoneserver daemon in
addition to the maradns daemon. Both daemons use the same mararc
configuration file; there are a few mararc variables that affect
the zoneserver daemon but not the maradns daemon (and vice
versa).
When setting up a master DNS server, only one additional mararc
variable needs to be set up, zone_transfer_acl. This variable
needs to list the IPs of the slave DNS servers that will
transfer zones from the master server. For example, if the slave
DNS servers have the IPs 192.168.72.34, 10.34.56.98, and
172.17.23.37, the line will look like this:
zone_transfer_acl = "192.168.72.34, 10.34.56.98, 172.17.23.37"
If you do not know the IPs of the slave DNS servers, you can
allow any computer on the internet to connect to your zone
server thusly:
zone_transfer_acl = "0.0.0.0/0"
Note that this will make potentially private information public.
Something like this can also be done:
zone_transfer_acl = "192.168.42.0/24, 10.0.0.0/8,
172.19.0.0/16"
This will allow any IP starting with "192.168.42" to connect to
the zone server, any IP starting with "10" to connect to the
zone server, and any IP starting with "172.19" to connect to the
zone server.
Here is a example mararc file which is on the ip 10.1.2.3, and
serves the zone example.com to the IPs 192.168.72.34,
10.34.56.98, and 172.17.23.37:
ipv4_bind_addresses = "10.1.2.3"
chroot_dir = "/etc/maradns"
csv2 = {}
csv2["example.com."] = "db.example.com"
zone_transfer_acl = "192.168.72.34, 10.34.56.98, 172.17.23.37"
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How SOA records affect slave zone servers
The SOA record tells the slave zone servers how often to check
to see if a zone file needs to be reloaded. Here is what a SOA
record looks like:
example.com. SOA example.com. hostmaster@example.com. 1 7200
3600 604800 1800
The first field is the name of the zone this SOA record is for.
The second field tells the csv2 parser that this is a SOA
record.
The third field is the name of the machine which is the DNS
master server for this zone.
The fourth field is the email address for the person in charge
of this zone.
The fifth field (first numeric field) is what is called the
"serial" number. This number is used by slave DNS servers to see
if the zone file has changed. This number should be increased
every time a zone file is changed. MaraDNS, when generating a
synthetic SOA record, looks to see when the zone file was last
changed, and uses a time stamp which updates every six seconds
as the SOA serial number.
The sixth field (second numeric field) is the "refresh" for the
domain; this is how often (in seconds) a slave DNS server could
check to see if the serial on the master DNS server has changed.
The seventh field (third numeric field) is the "retry" for the
domain; when the master DNS server is down, this is how often
the slave DNS server will check to see if the master DNS server
is up again. This value, like all time values, is in seconds.
The eight field (fourth numeric field) is the "expire" for the
domain; this is how long the slave server will wait before no
longer attempting to get a zone from a master DNS server when
the master DNS server is down. This should be a large value.
The ninth field (fifth numeric field) is the "minimum" for the
domain; this does not affect how MaraDNS processes a zone file
and is not used by slave DNS servers (it determines the
default/minimum TTL with other DNS servers).
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The zoneserver program can also be used to serve other DNS
records over TCP; see the file dnstcp for details.
