SANOG 41 DNS workshop
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Reverse DNS Lab (IPv4)

IPv4 limitation

Goal of this lab is to setup a reverse DNS zone for IPv4/IPv6 and host it on your authoritative DNS server. Due to shortage of IPv4, we will use private IPv4 but public IPv6. Because it’s private IPv4, the full resolution chain will not work with it but setup can be verified by directly querying server.

Find the IPv4 and IPv6 prefixes you are supposed to use from hostname page.


Step 1 - Deteremine rDNS Zone

Check your IPv4 rDNS prefix. E.g for attendee 01 it is:

Read each octet as:

Octet Value
First 10
Second 11
Third 1
Fourth 0

First three octets here determine the zone and fourth give PTR value. To create zone, write zone in reverse as:

Third Octet . Second octet . First octet .

This gives us:

Step 2 - Add rDNS Zone in auth servers

Add this in PowerDNS admin by clicking on “Create Zone”

Step 3 - Create rDNS PTR records

Create following two records:

  1. Point 1st IP to -
  2. Point 2nd IP to -

Select “Zones” from the top tab and open the respective zone

Click “+ Add record” and put “1” in the name for first or “2” for second. This corresponds to the last octet of the IPv4. Click “Save” for each record and “Save changes” on the top to push changes to the auth DNS server.

Step 4 - Verify rDNS PTR records

Once added, query your primary or secondary auth server directly (due to IPv4 limitation) and verify that you see records.

anurag@desktop ~> dig -x +short
anurag@desktop ~> 

anurag@desktop ~> dig -x +short
anurag@desktop ~> 

Once finished, proceed with rDNS lab for IPv6. Instructions here.