Reverse DNS Question
Jim Mercer
jim at reptiles.org
Wed Apr 21 06:31:44 UTC 2010
On Tue, Apr 20, 2010 at 10:26:17AM -1000, Antonio Querubin wrote:
> On Tue, 20 Apr 2010, James Martin wrote:
> >What is the purpose for this besides resolving name-based reverse lookups?
> >Are there any definitive guides out there on how this works (besides the
> >ARIN site)?
>
> It's for resolving address-based lookups. When ARIN allocates address
> space to you, you now become responsible for the reverse-lookups for that
> allocated address range.
with forward DNS, anyone can map a domain to any arbitrary IP address, such
as mapping www.example.com to the same IP address as big-popular-bank.com.
there is nothing to prevent this, and in some cases it is acceptable, and in
some cases, possibly nefarious.
when the registeries (ARIN/RIPE/APNIC/etc) require the "owner" of an ip block
to define name servers for reverse maps, it provides a mechanism to double
check if a domain/ip-addr map is valid.
it isn't 100%, for sure, but, it is substantially better than nothing.
in this sense, www.example.com can have an A record of 192.168.1.1
and, through the reverse map, 1.1.168.192.in-addr.arpa will have a PTR record
of "www.example.com"
in fact, there can be multiple PTR records, in case you have multiple
domains pointing at the same IP address.
on many unix(-ish) systems, the "host" command will show you the reverse PTR
record, if you run: host 192.168.1.1 , it might show:
user at hostname% host 192.168.1.1
1.1.168.192.in-addr.arpa domain name pointer www.example.com.
keep in mind, this will only work if the name servers registered for the ip
block actually contain data.
check out:
http://en.wikipedia.org/wiki/Reverse_DNS_lookup
and, go to "Guide to reverse zones" in:
http://www.apnic.net/__data/assets/pdf_file/0009/9792/Reverse-DNS-manual.pdf
hope this is helpful
--
Jim Mercer jim at reptiles.org +92 336 520-4504
"I'm Prime Minister of Canada, I live here and I'm going to take a leak."
- Lester Pearson in 1967, during a meeting between himself and
President Lyndon Johnson, whose Secret Service detail had taken over
Pearson's cottage retreat. At one point, a Johnson guard asked
Pearson, "Who are you and where are you going?"
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