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Monday, November 17, 2014

$GENERATE A records using BIND. Match forward and rDNS

Hi,
This post is very short but perhaps very useful. There is less documentation on the Internet than expected.

Objective: 
a) Set the reverse DNS and forward DNS match for a / 24 in BIND9 using $GENERATE.

Requirements: 
- A  /24 network (of course, you can adapt the example to other networks)
- BIND9
- We will use A and PTR records

Example: 
Network: 192.168.30.0/24
Domain: example.com

Let's make the rDNS for 192.168.30.X resolved to: X.client.example.com
Similarly, X.client.example.com to resolve to 192.168.30.X

It would be like this:
192.168.30.1 ---> 1.client.example.com
192.168.30.2 ---> 2.client.example.com
192.168.30.3 ---> 3.client.example.com
1.client.example.com ---> 192.168.30.1
2.client.example.com ---> 192.168.30.2
3.client.example.com ---> 192.168.30.3
(Etc)

Steps: 
We create reverse zone in /etc/bind/named.conf.

a) The reverse zone:

zone "30.168.192.in-addr.arpa" {
type master;
file "30.168.192.in-addr.arpa.db";
allow-query {any; };
};


After that, then in file 30.168.192.in-addr.arpa.db place the following: 

$TTL    86400 ; 24 hours, could have been written as 24h or 1d
@  1D  IN        SOA localhost.     hostmaster.example.com. (
                              2002022401 ; serial
                              3H ; refresh
                              15 ; retry
                              1w ; expire
                              3h ; minimum
                             )
; Name servers for the zone - both out-of-zone - no A RRs required
                        NS      localhost.

$GENERATE 1-255 $ PTR $.client.example.com.


b) The forward DNS is doing the following in the client.example.com zone file: 

$TTL    86400 ; 24 hours, could have been written as 24h or 1d
@  1D  IN        SOA localhost.     hostmaster.example.com. (
                              2002022401 ; serial
                              3H ; refresh
                              15 ; retry
                              1w ; expire
                              3h ; minimum
                             )
; Name servers for the zone - both out-of-zone - no A RRs required
                        NS      localhost.

$GENERATE 1-255.client.example.com $ A 192.168.30.$



Testing: 
#dig -x 192.168.30.3 (reverse dns) 
#dig 3.cliente.ejemplo.com (forward dns) 



P.S. As usual there can be more than way of doing this kind of things.

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