GENDNS(1) 06:53:19 GENDNS(1)
NAME
gendns - update the DNS zone files from flat relational tables
SYNOPSIS
gendns [ -d dbdirectory ] [ -l dhcp_lease_file [ -v ] [ -F ]
DESCRIPTION
Updates the DNS zone files.
gendns is a back end to the updatehosts command. It should normally
only be invoked from the updatehosts command.
gendns converts a set of flat (relational) files into the standard DNS
zone file format. All input files are kept in the dbdirectory which
can be specified by the -d command line option. All output is placed
in the current directory. When run under updatehosts the current
directory is normally /var/named and the input directory is normally
/var/named/db. However, these defaults may be overridden. See the
updatehosts(1) manual page for details.
The -l option specifies the location of the dhcp_lease file. It
defaults to /etc/dhcpd.leases. gendns has the capability of reading
the lease file information and generating name to IP address mappings
when the IP address of a host is set to "dynamic".
The -v option generates additional output on the progress of the zone
file generation.
The -F option forces a zone files serial number to be updated even
though no changes were made to the zone file. This was the default
behavior before updatehosts 1.0.2. Now if the information in a zone
file does not change, the zone files serial number is not not updated.
This saves slave zone transfers when updatehosts handles a large number
of zone files.
Input File Formats
gendns uses readinfo (see readinfo(1)) to preprocess the input files.
The format of each file consists of a set of records separated into
fields. Care should be taken to insure the field names are not
altered. Otherwise gendns will complain. Each fields attributes
should be examined carefully when editing the input files. Usually,
default suffixes and prefixes are added so domain names and IP
addresses can be written in a shorthand fashion. However, the output
from readinfo read by gendns is expected to have fully qualified domain
names and full dotted quad IP addresses. Each files record structure
is described as follows:
main: Contains information about each host. The fields in this file
are as follows:
host: The domain name of the host.
ip: The IP address of the host. May be set to "dynamic" when
the dynamic addressing of DHCP is in use.
ether: The hardware MAC address of the host.
hard: The hardware type of the host.
os: The operating system of the host.
contact:
The name of a contact person or user of the host.
ptr: Either "yes" or "no". Tells gendns whether to generate
the reverse zone entry for the host (e.g.the IP address
to domain mapping zone). The default (empty) value is
"yes".
ttl: Specifies the time to live field for both the address (A
record type) and the reverse PTR record if generated.
Time is specified in seconds. If this field is empty the
default ttl for the zone (specified in the SOA record) is
used.
gendns only needs entries for the domain and ip fields. The other
fields may be empty.
cname: Species information about hosts and their aliases. The fields
are:
host: The domain name of a host
alias: The alias for the host
ttl: The time to live for this record
mx: Specifies information about MX (mail exchanger) records.
domain:
The mail domain name
priority:
The MX record priority
host: The domain name of the mail forwarder
ttl: The time to live for this record
ns: Specifies information about nameserver records.
domain:
The nameserver domain
server:
The domain name of the server for each domain
ttl: The time to live for this record
soa: The SOA (start of authority) record information for each domain
served.
domain:
The domain (zone) this server is authoritative for
server:
The domain name of the primary server for this domain
contact:
Email address of domain contact. Per DNS format rules
the @ in the address is specified as a ".".
refresh:
The refresh interval for this zone in seconds
retry: The retry interval for this zone in seconds
expire:
The authoritative expiration time in seconds for sec
ondary servers which have not been refreshed within the
interval specified.
min: The minimum time to live for resource records within this
zone without a ttl.
checknames:
Specifies how illegal domain names are treated within
this zone. Only works with version 8 of bind. The 3
legal values of this field are:
warn: Warns about illegal names, but allows the names
within a zone. Emits an error message about the
name.
ignore:
Ignores illegal names within the zone.
fail: Emits error messages about illegal names and does
not load the zone.
notify:
If this field is "yes", all secondary servers are noti
fied about updates. Only works with Version 8 of bind.
secondary
Specifies zones this server will act as a secondary server for.
In bind version 8 a secondary server is known as a slave server.
domain:
The name of the domain being served.
ip: The IP address of an authoritative server for this zone.
Multiple servers may be specified by separating the IP
address with commas.
checknames:
Same values as the checknames field in the soa records.
global:
Contains global parameters applicable to all zones.
directory:
The name of the directory containing the generated zone
files.
cache: Name of the root cache file
forwarders:
list of optional forwarders for this server. This field
is usually empty
checknames:
Same as the checknames field found in each zone, but
applies to all zones. Individual zones may override this
value.
slave: Sets up this server as a slave server (stub in bind ver
sion 8 parlance). Can be either "yes" or "no". The
default is "no".
Zone File Generation
Zone file generation is driven off of the soa file. Each domain speci
fied in the soa file generates a separate DNS zone file. The name of
the zone file is the same as the name of the domain field for forward
zones. For a zone under in-addr.arpa (e.g. IP address to name map
ping), the name of the zone file is the IP network address of the zone
with an "f." prefix. For classless in-addr.arpa delegation of Class C
addresses, the assumption is the delegation is done per RFC2317. The
zone file name replaces the "/" in the delegation reference with a "-".
For example delegating the subnet of 199.10.2.0/28 means delegating the
zone 2/28.0.10.199.in-addr.arpa. The zone file in this case would be
named f.199.10.2.0-28. A zone file is only generated if it appears in
the soa file. Records in the other input files which are not members
of a generated zone are silently ignored.
The program scans all the input files for domain records within each
zone and generates all the records for the zone.
The serial number field is updated automatically for each new zone.
The serial number is encoded from the real time clock value as yyyymmd
dxx, where yyyy is the 4 digit year, mm is the 2 digit month, dd is the
2 digit day, and xx is a 2 digit number between 00 and 99. This gives
a granularity between updates of about 15 minutes.
Bootstrap File Generation
gendns also generates the bootstrap file for either version 4 or ver
sion 8 of the bind nameserver. The generated bootstrap file is put in
the current directory (usually /var/named). To allow the nameserver to
use the newly generated bootstrap file it is customary to link it to
either /etc/named.boot for a version 4 nameserver or /etc/named.conf
for a version 8 nameserver.
Error Handling
An error message is issued for any CNAME (alias) record which is ille
gal. A CNAME record must only appear at a leaf node in the DNS hierar
chy. Any record which violates this rule is dropped. A warning message
is issued for any duplicate IP address or duplicate A records. These
are warnings only, since duplication of domain names or IP addressed
may be desirable.
See also
updatehosts(1)
4th Berkeley Distribution $Date: GENDNS(1)
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