September 2008


There may come a time when your DNS server is the authoritative DNS for a client or customer that has secured an IP block from a 3rd party, perhaps for T1 or DSL service. They want to use one of the IP addresses for an email server located in their office and have asked you to setup rDNS or Reverse DNS for the IP address specified. Since the IP address did not come from your ISP you cannot ask them to setup the rDNS for you. You must accept IP delegation and configure your DNS server to give an authoritative response.

Here are 3 links that helped me figure this out:

I’m going to illustrate this using 10.x.x.x IP address ranges. This setup is for Bind DNS servers. You will be creating a zone for on your DNS server.

The scenario is that the client secured a new T1 line and wanted to use IP for an email server in their office.

On your DNS server, open a terminal window. Then edited /etc/named.conf and added this to the end:

zone “160/” {
type master;
file “/var/named/”;

That means that it has been added to the external view section of named.conf

I have to admit that I do not fully understand why some delegations may be looking for zone 160/ and others Both can contain the IP It may have something to do with this delegation being a /28 giving the client 16 IP addresses with 14 usable starting from

Save your changes then create a new zone DB named /var/named/

You can do this like this:

touch /var/named/

Then open /var/named/ and add:

; Zone file for 160/
$TTL 14400
@      86400    IN      SOA (
2008092801      ; serial, todays date+todays
14400           ; refresh, seconds
7200            ; retry, seconds
1209600         ; expire, seconds
86400 )         ; minimum, seconds
160/         IN      84600   NS
160/         IN      84600   NS           IN      14400   CNAME   162.160/
162.160/     IN      14400   PTR

Save and restart Bind. You can test your results here:


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