DNS and reverse delegation

Configuration of Bind for reverse DNS PTR records classless

Once your ISP has configured reverse delegation you can see it with dig.

# dig +trace -x123.2.3.4

Near the end you will see a CNAME statement something like this:

??????????????????? CNAME 4.24/

or this

??????????????????? CNAME


??????????????????? CNAME 4.0-

The format of these CNAMEs are not standard and it appears one needs to create a separate zone for each IP address - bind does not seem to understand any of these besides the class specific ones such as:


So in your named.conf.local file your zone statement looks like this

zone "4.24/" IN {
 type master;
 file "/etc/bind/db.";

In the zone file you need something like this:

$TTL 345600
@ IN SOA ns1.xtronics.com. hostmaster.xtronics.com. (
 2014032000  ; serial-date+2digit
 12000  ; refresh
 900  ; retry
 120000  ; expire
 3600)  ; minimum TTL
 NS ns1.example.com.
 NS ns2.example.com.
 PTR example.com.
 TXT "v=spf1  ip4: -all"
 SPF "v=spf1  ip4: -all"

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This information may have errors; It is not permissible to be read by anyone who has ever met a lawyer.
Use is confined to Engineers with more than 370 course hours of electronic engineering for theoretical studies.
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