Date: Thu, 27 Mar 2003 19:15:30 +0000 (GMT) From: Jan Grant <Jan.Grant@bristol.ac.uk> To: James Earl <mtntrip@telus.net> Cc: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: Reverse DNS and single IP address space Message-ID: <Pine.GSO.4.44.0303271910140.21755-100000@mail.ilrt.bris.ac.uk> In-Reply-To: <20030327185204.GA645@comp4.ici.net>
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On Thu, 27 Mar 2003, James Earl wrote: > On 2003.03.27 11:38 Victor Bondarenko wrote: > > On Thu, Mar 27, 2003 at 11:31:54AM -0700, James Earl wrote: > > [...] > > > Or, do I even need to worry about reverse DNS entries since my ISP > > > already has them setup? > > > > If your ISP has reverse DNS for your IP(s), there's really no point in > > you mapping them on your own. Your network might see whatever you've > > mapped, but the rest of the world will see what your ISP maps. > > I'm assuming if I can use nslookup [ip-address] to get my hostname, > that reverse DNS on the ISP is setup properly. Is this an okay > assumption? Not necessarily. Firstly, you want to know what nameserver you're getting that response from. Secondly, if the nameserver you're getting the response from belongs to the ISP, they might _think_ the reverse map is set up correctly, but upstream nameservers may disagree. You might want to pick a publicly-available nameserver and query it; alternatively, use nslookup or dig to follow the chain "by hand" from a root nameserver. The odds are you're ok, but checking by hand involves a little more work. You can do something like: > dig @a.root-servers.net 1.0.168.192.in-addr.arpa. ptr and you'll get a bit of the prefix and the next nameserver down to query (probably a list of them). Pick one and repeat the request until you get your ptr record back. That's what the rest of the world would do, effectively. Cheers, -- jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/ Tel +44(0)117 9287088 Fax +44 (0)117 9287112 http://ioctl.org/jan/ I shave with Occam's Razor.
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