danicoin/external/unbound/libunbound/python/doc/examples/example1b.rst
Erik de Castro Lopo a85b5759f3 Upgrade unbound library
These files were pulled from the 1.6.3 release tarball.

This new version builds against OpenSSL version 1.1 which will be
the default in the new Debian Stable which is due to be released
RealSoonNow (tm).
2017-06-17 23:04:00 +10:00

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.. _example_reverse_lookup:
Reverse DNS lookup
==================
Reverse DNS lookup involves determining the hostname associated with a given IP
address.
This example shows how reverse lookup can be done using unbound module.
For the reverse DNS records, the special domain in-addr.arpa is reserved.
For example, a host name for the IP address ``74.125.43.147`` can be obtained
by issuing a DNS query for the PTR record for address
``147.43.125.74.in-addr.arpa.``
Source code
-----------
::
#!/usr/bin/python
import unbound
ctx = unbound.ub_ctx()
ctx.resolvconf("/etc/resolv.conf")
status, result = ctx.resolve(unbound.reverse("74.125.43.147") + ".in-addr.arpa.", unbound.RR_TYPE_PTR, unbound.RR_CLASS_IN)
if status == 0 and result.havedata:
print "Result.data:", result.data.domain_list
elif status != 0:
print "Resolve error:", unbound.ub_strerror(status)
In order to simplify the python code, unbound module contains the
:meth:`unbound.reverse` function which reverses the hostname components.
This function is defined as follows::
def reverse(domain):
return '.'.join([a for a in domain.split(".")][::-1])