NAME

       axfrdns - a DNS zone-transfer server.

DESCRIPTION

       axfrdns  reads a zone-transfer request in DNS-over-TCP format from its standard input, and
       responds with locally configured information.

Configuration

       Normally axfrdns is set up by the axfrdns-conf(8) program.

       axfrdns runs chrooted in the directory specified by the $ROOT environment variable,  under
       the uid and gid specified by the $UID and $GID environment variables.

       Normally  axfrdns  runs under tcpserver(1) to handle TCP connections on port 53 of a local
       IP address.

       tcpserver(1) is responsible for rejecting connections from hosts not authorized to perform
       zone transfers.

       axfrdns can also run under secure connection tools offering an UCSPI-compliant interface.

       axfrdns  looks  up  zone-transfer  results  in data.cdb, a binary file created by tinydns-
       data(8).  It also responds to normal client queries, such as SOA  queries,  which  usually
       precede zone-transfer requests.

       axfrdns allows zone transfers for any zone listed in the $AXFR environment variable.

       $AXFR is a slash-separated list of domain names.  If $AXFR is not set, axfrdns allows zone
       transfers for all zones available in data.cdb.

       axfrdns aborts if it runs out of memory, or has trouble reading data.cdb,  or  receives  a
       request  larger  than  512  bytes,  or  receives  a truncated request, or receives a zone-
       transfer request disallowed by $AXFR, or receives a request not answered by  data.cdb,  or
       waits 60 seconds with nothing happening.

Further notes on zone transfers

       axfrdns  provides  every  record  it  can find inside the target domain.  This may include
       records in child zones.  Some of these records (such as glue  inside  a  child  zone)  are
       essential;  others are not.  It is up to the client to decide which out-of-zone records to
       keep.

       axfrdns does not provide glue records outside the target domain.

       The zone-transfer protocol does not support timestamps.  If a record is  scheduled  to  be
       created  in  the  future,  axfrdns  does  not  send it; after the starting time, the zone-
       transfer client will continue claiming that the record doesn't exist,  until  it  contacts
       axfrdns again.  Similarly, if a record is scheduled to die in the future, axfrdns sends it
       (with a 2-second TTL); after the ending  time,  the  zone-transfer  client  will  continue
       providing the old record, until it contacts axfrdns again.

       Zone-transfer clients rely on zone serial numbers changing for every zone modification.

       tinydns-data(8)  uses  the modification time of the data file as its serial number for all
       zones.  Do not make more than one modification per second.

       BIND's zone-transfer client, named-xfer, converts zone-transfer data to zone-file  format.
       Beware  that  zone-file  format  has  no generic mechanism to express records of arbitrary
       types;

       named-xfer chokes if it does not recognize a record type used in data.cdb.

SEE ALSO

       axfrdns-conf(8), tinydns-data(8), tcpserver(1)

       http://cr.yp.to/djbdns.html

                                                                                       axfrdns(8)