DNS reverse lookup

Ilithios · New Member Joined: Dec 8, 2002 Posts: 6 Location: Greece

Hello there, great site again and very good work

i have some questions about reverse dns lookup. how does the whole reverse lookup system works? suppose i have some class c networks, how can i define which dns server will lookup for each one ( reverse ).
and one last question that is troubling me is this : let's suppose we have a class c network ( 255 ips ). and i have 2 nameservers. how can i have one of them reverse lookup some ips and the the other nameserver the rest of them ?

thank you

Manip · Posted: Thu Feb 13, 2003 4:39 am Post subject: DNS reverse lookup

I am going to assume you are working in windows...:s to define which DNS server you will be using look under your 'Local Area Connection' > 'Internet Protocol (TCP/IP)' You will see Obtain DNS server address automatically, which generally means if you have a web proxy it will use the proxy specified by that.
To define a custom proxy change to 'Use The following DNS server addresses:' and enter a Primary, then a secondary (if you have it), the secondary is the backup if your first one goes down.
To do what you said (Have two DNS with separate records) you could split the computers on your network up and specify different DNS servers or have the primary DNS server point to the secondary DNS server to get address X.

1. Primary give me www.intranet.com
2. Ok you can find it by going and looking at another DNS server >> 10.0.0.2
3. Secondary DNS can I have www.intranet.com
4. Yes 10.0.0.100

wrath_child · Posted: Thu Feb 13, 2003 10:44 pm Post subject: DNS reverse lookup

Hello,

say you are assigned addresses

range 1. 192.168.0.0/24
range 2. 192.168.1.0/24

and you have 2 DNS servers

DNS 1. ns1.yourdomain (10.0.0.1)
DNS 2. ns2.yourdomain (10.0.1.1)

now you want to configure reverse delegation for both ranges with the following settings:

Pri DNS for range 1 - DNS 1
Sec DNS for range 1 - DNS 2

and

Pri DNS for range 2 - DNS 2
Sec DNS for range 2 - DNS 1

--- named.conf on 10.0.0.1
zone "0.168.192.IN-ADDR.ARPA" {
type master;
file "0.rev";
};

zone "1.168.192.IN-ADDR.ARPA" {
type slave;
file "1.rev";
masters { 10.0.1.1 };
}
---
--- named.conf for 10.0.1.1
zone "0.168.192.IN-ADDR.ARPA" {
type slave;
file "0.rev";
masters { 10.0.0.1 };
};

zone "1.168.192.IN-ADDR.ARPA" {
type master;
file "1.rev";
}
---

0.rev and 1.rev files should contain records like:

SOA record here
...
1 IN PTR host1.
2 IN PTR host2.
...

after you have done configuration on your server dont forget to ask your ip addresses provider to update their nameservers for reverse delegation on your ip ranges.

Hope this helps.

Ilithios · New Member Joined: Dec 8, 2002 Posts: 6 Location: Greece

Thank you very much wrath_child, indeed it helped and thank you Manip though the question was more relevant to what wrath_child answered.
I have this last question. Suppose i have the network 192.168.0/24 and 192.168.0.1 is my primary dns server. I want for some particular IPs belonging to this range ( say for example 5 IPs ) do their reverse lookup by another nameserver ( no subnetting ).
Example :
for IPs : 192.168.0.0-249 i want my pri dns to do the reverse resolving
and for the IPs : 192.168.0.250-254 to have another dns do my reverse resolving ( the second dns is still in this network )
Is that possible and if so, how?

thank you again

Ilithios · New Member Joined: Dec 8, 2002 Posts: 6 Location: Greece

Thanx again

wrath_child · Posted: Fri Feb 14, 2003 10:13 pm Post subject: DNS reverse lookup

Hello Ilithios,

The thing you need is called "Classless reverse delegation" and is described in document below:
http://www.faqs.org/rfcs/rfc2317.html

I don't think I can explain the subject better

Best regards