Date: Sat, 15 Sep 2001 17:10:26 +0100 From: setantae <setantae@submonkey.net> To: "Russell A. Khurshudian" <russell_k@acedsl.com> Cc: freebsd-questions@freebsd.org Subject: Re: Reverse DNS Delegation Message-ID: <20010915171026.A9003@rhadamanth> In-Reply-To: <002c01c13d60$54a55280$0200a8c0@networld>; from russell_k@acedsl.com on Fri, Sep 14, 2001 at 05:00:43PM -0400 References: <002c01c13d60$54a55280$0200a8c0@networld>
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On Fri, Sep 14, 2001 at 05:00:43PM -0400, Russell A. Khurshudian wrote: > May someone please explain Reverse DNS and it's uses. Also, say i want > to get Reverse DNS delegation from my ISP, what information do i need > to provide them with? Thank you. You'll need to provice your ISP with the hostname and IP address. Here's a little thing I wrote about reverse DNS, might help explain how it works. It tails off a bit at the end, because I got bored writing it... Reverse DNS When a connection is made to a computer, the only information regarding the source of the connection that is available to the computer receiving the packet is the IP address that it came from. In addition, sometimes it is just not possible to remember all the IP addresses of all the hosts in a network, for example, I am totally unable to recall that 194.168.54.49 is mailrelay1-gui.server.ntli.net, and simply seeing the IP in a mail log is not of use to me. If we can map hostnames to IP addresses using DNS, it's reasonable to ask for a way to map IP addresses to hostnames. This is achieved with a special domain called in-addr.arpa. (inverse address, .arpa used to be the only top level domain) and a special resource record - the PTR record. The PTR Resource Record PTR means Pointer. The domain in-addr.arpa. is broken into a number of subdomains which correspond to an IP address, backwards. In order to discover which host has the IP address 172.27.65.12, your machine would send a query for the PTR record for 12.65.27.172.in-addr.arpa. While this may seem very strange, if you think about the way that domains and subdomains can be delegated, it makes perfect sense. For example, ntl have been delegated the IP block 194.168.0.0 - 194.168.255.255 Due to the above, it's now very easy to simply delegate 168.194.in-addr.arpa to ntl, whereas if it where done forwards then they would need to be delegated a part of 0.in-addr.arpa, a part of 1.in-addr.arpa, a part of 2.in-addr.arpa, and so on. So a PTR record simply looks like this : 49.54.168.194.in-addr.arpa. IN PTR mailrelay1-gui.server.ntli.net. The IP address is backwards - this doesn't make it hard. Ceri -- keep a mild groove on To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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