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@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@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?"