Forwarding reverse DNS queries

[Barry Margolin]

In article <bpjef1$2u0e$1 at sf1.isc.org>,
Thomas Smith  <tom at openadventures.org> wrote:
>A customer of mine is having issues with their reverse DNS. The 
>situation is this:
>
>They lease a block of IPs from me. The customer has his own DNS servers 
>(two of them). Forward lookups work fine, but reverse lookups don't work.
>
>I understand what the problem is--reverse lookups are being directed to 
>my servers since I own the IP block in question.
>
>The question is: How do I forward reverse DNS lookups for a specific 
>block of IPs to his servers?

If the block is smaller than a /24, you should use the technique described
in RFC 2317.

Suppose your network is 192.168.10.0/24 and his block is 192.168.10.16/28.
Your server should have the 10.168.192.in-addr.arpa zone on it.  In that
zone file you should enter:

16/28 IN NS ns1.them.com.
      IN NS ns2.them.com.
16    IN CNAME 16.16/28
17    IN CNAME 17.16/28
....
31    IN CNAME 31.16/28

The customer configures their servers as authoritative for the
16/28.10.168.192.in-addr.arpa zone, and puts their PTR records in its zone
file.

It's also usually a good idea for each of you to be stealth slaves for the
other's reverse zone.

-- 
Barry Margolin, barmar at alum.mit.edu
Level(3), Woburn, MA
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