Reverse DNS Question
jim at reptiles.org
Wed Apr 21 01:31:44 CDT 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, 126.96.36.199.in-addr.arpa will have a PTR record
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
188.8.131.52.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.
and, go to "Guide to reverse zones" in:
hope this is helpful
Jim Mercer jim at reptiles.org +92 336 520-4504
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