Howto reverse mapping ?

[Barry Margolin]

In article <38A310BD.7FD108E at daimlerchrysler.com>,
Kevin Darcy  <kcd at daimlerchrysler.com> wrote:
>John wrote:
>
>> > The range of IP is 212.208.151.112 to 212.208.151.127....
>> > What shall I do ? Shall I do a file for 151.208.212.in-addr.arpa ??
>> >
>>
>> yes 151.208.212.in-addr.arpa will do with  IN PTR records for your ip
>> addreses
>>
>> but for it to be successfully done you isp should also put in their
>> 151.208.212.in-addr.arpa zone
>>
>> 112  IN NS  w.x.y.z
>> 113  IN NS  w.x.y.z
>> ...
>> ...
>> ...
>> 127  IN NS  w.x.y.z
>>
>> where w.x.y.z is the DNS server serving your 151.208.212.in-addr.arpa zone
>
>(I hope you weren't implying that "w.x.y.z" is an IP address, since that
>would be illegal on the right-hand side of an NS record.)
>
>You know, this scheme might actually work (although I haven't actually tried
>it). Other nameservers would be fooled into thinking that there is a
>112.151.208.212.in-addr.arpa zone, for example, send the PTR query to the
>w.x.y.z server and get an authoritative answer. As long as they didn't look
>too closely at the Authority Section, they'd probably just accept the answer
>and go on their merry way.

Actually, the authority section could be a real problem with this scheme.
Many servers will cache the authority section, so they'll be fooled into
thinking that his server is authoritative for all the entire class C, and
they'll forget about the ISP's servers.

Also, if his users use this server as their resolver, they won't be able to
do reverse lookups of other addresses in the same class C, because it
thinks it's authoritative for the entire block.

If he really wants to have delegations for each address, he should create a
separate zone for each:

zone "112.151.208.212.in-addr.arpa" {
  type master;
  file "db.212.208.151.112";
};
zone "113.151.208.212.in-addr.arpa" {
  type master;
  file "db.212.208.151.113";
};
and so on.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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