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Bind9 reverse Delegation

Posted on 2003-11-05
Medium Priority
Last Modified: 2012-05-04
I have a client that we are hosting that is using a full class C.  We are wanting to be able to delegate the class C to them for reverse lookups.   How do you set that up in bind?  I am familiar with standard reverse files, I have never had to setup a reverse delegation to another server though.

Question by:atebit
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LVL 40

Expert Comment

ID: 9689066
Assuming that you have in-addr.arpa authority for the Class B that the Class C is part of you can delegate it to them with:

n.n.n.in-addr.arpa.         86400  IN  NS  ns1.their-dom.tld.
n.n.n.in-addr.arpa.         86400  IN  NS  ns2.their-dom.tld.

in the reverse zone for the Class B. This is covered in detail in Chapter 9 of "DNS and BIND".

Author Comment

ID: 9689591
We have in-addr.arpa authority for a /21 (XXX.XXX.128.XXX - XXX.XXX.135.XXX)

Currently today I have a separate in-addr.arpa file for each of my class C's.  Is there a better way to do this?  

LVL 13

Accepted Solution

td_miles earned 2000 total points
ID: 9698660
The Class C reverse zones have already been delegated to you and a zone can only be delegated once (ie. you can't "forward" the delegation on to them). You have two options:

1. contact the authority for the Class B that your Class C addresses fall under and get them to redelegate reverse DNS for the Class C you are giving to the client directly to the clients name servers.
2. Leave your server as authorative for the clients' Class C, but make that Class C zone a slave/secondary to a primary one that the client manages on their name server, that way your server will pull the data from theirs.

Reverse DNS is delegated along the octec boundaries and cannot be aggregated. Each Class C address block is a seperate domain. To compare, think about if you had two domains:


Is there any way of aggregating these two domains into a single file ? No, because they are totally seperate domains, as are each of your Class C address block domains. You can aggregate them for routing purposes, but there is no such aggregation for reverse DNS. (so your method for seperate files for each Class C is correct)



Author Comment

ID: 9703342
Thanks for the reply.  I really like the slave idea.... That will help with some other issues :)  


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