From owner-freebsd-questions Mon Nov 1 11:54:34 1999 Delivered-To: freebsd-questions@freebsd.org Received: from D2SI.COM (D2SI.COM [63.224.10.2]) by hub.freebsd.org (Postfix) with ESMTP id D33E814A2F for ; Mon, 1 Nov 1999 11:54:19 -0800 (PST) (envelope-from ajk@paw-in-eye.net) Received: (from ajk@localhost) by D2SI.COM (8.9.3/8.9.3) id NAA05346; Mon, 1 Nov 1999 13:54:03 -0600 (CST) (envelope-from ajk) From: Alec Kloss Message-Id: <199911011954.NAA05346@D2SI.COM> Subject: Re: Reverse DNS lookup In-Reply-To: <4.1.19991031213125.009407e0@mail.udel.edu> from John at "Oct 31, 1999 9:33:50 pm" To: papalia@UDel.Edu (John) Date: Mon, 1 Nov 1999 13:54:03 -0600 (CST) Cc: dan@dpcsys.com, freebsd-questions@FreeBSD.ORG X-Mailer: ELM [version 2.4ME+ PL43 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG John said: > > > >> merlin# nslookup 63.224.53.3 > >> Server: copland.udel.edu > >> Address: 128.175.xx.xx > >> *** copland.udel.edu can't find 63.224.53.3: Non-existent host/domain > > > >That's cause there is no reverse for that IP. It's from a /25 subnet > >and US West probably doesn't delegate less than a /24 for in-addr.arpa Actually, they do, but they're not doing it exactly in line with the RFC for reasons involving their internal DNS management software. I had to get a friend of mine who works there to set it up. They use NS records on each address to point it to your own nameservers. Check out 63.224.10.1. It does appear that 63.224.53.3 is not assigned a reverse. > Could you do me a favor and explain all that? I have no idea what /25 > subnet and in-addr.arpa actually mean :) /25 subnet means the first 25 bits of the address correspond to a network and the last 7 correspond to a particular node on that network. Once upon a time, it was assumed that addresses less than 127.0.0.0 were /8 (aka. Class A), but this is no longer true. It appears that Network Solutions divided 63.x.x.x into /12 Default Server: localhost.d2si.com Address: 127.0.0.1 > set type=ptr > 224.63.in-addr.arpa Server: localhost.d2si.com Address: 127.0.0.1 224.63.in-addr.arpa origin = ns1.uswest.net mail addr = hostmaster.uswest.net serial = 318 refresh = 28800 (8H) retry = 7200 (2H) expire = 604800 (1W) minimum ttl = 86400 (1D) > 63.in-addr.arpa Server: localhost.d2si.com Address: 127.0.0.1 Authoritative answers can be found from: IN-ADDR.arpa origin = A.ROOT-SERVERS.NET mail addr = hostmaster.INTERNIC.NET serial = 1999110102 refresh = 1800 (30M) retry = 900 (15M) expire = 604800 (1W) minimum ttl = 86400 (1D) The in-addr.arpa DNS domain is used for reverse lookups. The idea is that reverse lookups should be delegated like forward ones are, in a hierarchical fashion. So, to find the name for a given address, you follow a hierarchy like this: arpa contains in-addr contains 63 contains 224 contains 53 contains 3, so you construct a DNS query for the name 3.53.224.63.in-addr.arpa. Also, note that you are looking for a particular type of record, a PTR record, so you should tell nslookup that using set type=ptr The problem with the above hierarchical scheme is that authority for reverse lookups no longer necessarily falls at the dots. So, the original scheme assumed that every address like 63.224.53.* was controlled by the same entity. It is becoming increasingly common for this not to be the case, so USWest is using a NS record to delegate the responsibility, like this: ajk@hamlet ~% nslookup Default Server: localhost.d2si.com Address: 127.0.0.1 > server ns1.uswest.net Default Server: ns1.uswest.net Address: 204.147.80.5 > set type=ns > 1.10.224.63.in-addr.arpa Server: ns1.uswest.net Address: 204.147.80.5 Non-authoritative answer: 1.10.224.63.in-addr.arpa nameserver = hamlet.d2si.com 1.10.224.63.in-addr.arpa nameserver = othello.d2si.com Authoritative answers can be found from: hamlet.d2si.com internet address = 63.224.10.2 othello.d2si.com internet address = 63.224.10.1 > 3.53.224.63.in-addr.arpa Server: ns1.uswest.net Address: 204.147.80.5 *** ns1.uswest.net can't find 3.53.224.63.in-addr.arpa: Non-existent host/domain They clearly have not set this up yet for whoever this 63.224.53.3 box is. > And if that's the case (above) then that might be the problem on all my > reverse lookups that go bad. In essence all the problems I'm having are > with people using their desktops at work who ssh into my box. But when I > try out nslookup on servers from, for example, my old ISP, it works fine > both ways. If you're saying that your old ISPs nameservers can resolve 63.224.53.3, they have probably assumed control of the network erronously. If I am correct, your school should be able to resolve 63.224.10.1 (it can) but your old ISP will probably NOT be able to resolve 63.224.10.1. Hope this helps clear things up a bit. > Thanks again!!! > --John > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message