.TH axfr-get 8

.SH NAME
axfr-get \- a DNS zone-transfer client.

It sends a zone-transfer request
in DNS-over-TCP format to descriptor 7,
reads the results from descriptor 6,
and saves the results in a file.

.SH SYNOPSIS
Normally 
.B axfr-get
is run under 
.BR tcpclient (1),
which sets up descriptors 6 and 7 as a TCP connection to a remote host.

.B axfr-get 
.I z
.I fn
.I fn.tmp

.SH DESCRIPTION
.B axfr-get
performs a zone transfer for domain 
.IR z .
It writes the results to 
.I fn.tmp
in a format that can be used as input to
.BR tinydns-data (8).
If the zone transfer completes successfully,
.B axfr-get
atomically renames 
.I fn.tmp
as 
.IR fn .

.I fn.tmp
and 
.I fn
must be on the same filesystem.

.B axfr-get
writes the zone serial number as a comment at the top of
.IR fn.tmp .
It skips the zone transfer,
leaving 
.I fn
alone,
if
.I fn
already exists,
 
.I fn
has a serial number
matching the zone serial number,
and both serial numbers are nonzero.

Zone transfers often include duplicate records.
You should feed the 
.B axfr-get
results through
sort -u.

.B axfr-get
discards all records outside the domain 
.IR z .
It accepts records in child zones,
but it marks all child zones as non-authoritative, so
.BR tinydns (8)
will not report those records except as glue.
If you plan to merge the 
.B axfr-get
results
for a domain and a child of the same domain,
creating a file authoritative for both zones,
make sure to eliminate records in the first output
that are within the child zone.

.B axfr-get
will accept arbitrarily large zone transfers.
To limit the maximum file size to 1 megabyte,
run 
.B axfr-get
under 
.BR softlimit 
\-f 1048576.

.SH Compatibility notes

.B axfr-get
handles
BIND's RFC-1034-violating multiple-answers zone-transfer format.

.B axfr-get
does not precisely simulate BIND's handling of 
.IR *.dom .
Under BIND, records for
.I *.dom
do not apply to
.I y.dom
or
.I anything.y.dom
if there is a normal record for
.IR x.y.dom .
With 
.B axfr-get
and 
.BR tinydns (8),
the records apply to 
.I y.dom
and
.I anything.y.dom
except 
.IR x.y.dom .

.B axfr-get
does not precisely simulate BIND's handling of multiple IP addresses
for a single name.
When there are more than 8 addresses,
.BR tinydns (8)
selects a random set of 8 for each query.

.SH SEE ALSO
axfrdns(8),
tinydns(8),
tinydns-data(8),
tcpclient(1),
softlimit(8)
http://cr.yp.to/djbdns.html