1.. _example_reverse_lookup:
2
3==============================
4Reverse DNS lookup
5==============================
6
7Reverse DNS lookup involves determining the hostname associated with a given IP address.
8This example shows how reverse lookup can be done using unbound module.
9
10For the reverse DNS records, the special domain in-addr.arpa is reserved. 
11For 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.
12
13::
14
15	#!/usr/bin/python
16	import unbound
17	
18	ctx = unbound.ub_ctx()
19	ctx.resolvconf("/etc/resolv.conf")
20	
21	status, result = ctx.resolve(unbound.reverse("74.125.43.147") + ".in-addr.arpa.", unbound.RR_TYPE_PTR, unbound.RR_CLASS_IN)
22	if status == 0 and result.havedata:
23		print "Result.data:", result.data.domain_list
24	elif status != 0:
25		print "Resolve error:", unbound.ub_strerror(status)
26
27In order to simplify the python code, unbound module contains function which reverses the hostname components. 
28This function is defined as follows::
29
30	def reverse(domain):
31		return '.'.join([a for a in domain.split(".")][::-1])
32
33
34