CIDR is killing my nerves

David Tonhofer david.tonhofer at
Mon Mar 5 18:11:30 UTC 2001

Getting to it ;-)

>> In named.conf, you would have (in my case):
>> // our own reverse lookup
>> zone "" {
>>         type master;
>>         file "named.rev";
>>         allow-transfer {; };
>> };

>This is it. This is what I was looking for. But how does Bind know that the
>reverse lookup zone is from 224 to 239? Why didn't you tell your bind how
>much bits your subnet has?

Your BIND doesn't need to know that. If anyone is doing a reverse lookup
on any of your IP addresses, he'll actually just be asking for a PTR
record that has as owner a domain name in the domain. This
query will *naturally* percolate down to your nameserver. Your provider's
DNS will know to forward a query for (e.g. in my case) zone to *your* DNS.

>> And in named.rev, you would list the PTR records
>> for the CNAMES assigned by your provider to the
>> names corresponding to the machines on your subnetwork.
>> (which, in my case, all begin with,
>> which as you can notice, is the base address of my CIDR
>> subnetwork), thus:
>> $TTL 28800
>> 224             IN      SOA
>This here above is missing in my reverse lookup zone. But this I can also
>edit without my ISP doing anything.


>> (
>>                 2001020410 28800 7200 604800 86400 )
>>                 IN      NS
>>                 IN      NS
>> 225             IN      PTR
>> 226             IN      PTR
>> 227             IN      PTR
>> etc...
> But this is your slave dns here.

No, this baby is the master. And it's got at authorithy for
the zone "", so it can respond
to PTR queries for

etc...which are 'specially fixed (by the provider)' zone names,
of course and not zones derived from actual IP addresses.

I hope I'm explaining this correctly. I'm self-taught here.

Best regards,

	-- David

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