Reverse DNS configuration

Now I have the AS, the router, the upstream, I decided to know how reverse DNS works on the internet. It is really simple, I think it is the easiest part of the adventure.

Check to do before

Before doing all of this, you need to check if you have a mnt-domains row with your maintainer in it. If not, you can ask your LIR to give you the permission, if they don’t want you cannot configure cool rDNS records.

Get the “default” IPv6 reverse DNS

You have two methods to do this, you can calculate the IPv6 rDNS with the RIPE database or by using a rDNS calculator.

In my case, I did the job with this calculator and checked a second time with the RIPE database.

As I have a /48 and the 2a0f:85c1:d31::/48 IPv6 range, I remove all the 0 before the d31. So we have 1.3.d.0.1.c.5.8.f.0.a.2.ip6.arpa.

Yes I did the savage way.

Create the DNS zone

As I am confident enough to create but not to manage my own DNS server, I decided to go with Cloudflare DNS. I use it for all my domain names, so why not.

To register a rDNS zone we just have to follow the same protocol as a domain name, but in the domain name field, you just have to enter the rDNS we calculated above.

Add a rDNS record to our router

During the configuration Cloudflare asks you if you want to configure some records.

I use the xx::1/48 IP address on my router, so the record name will be 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 and it will take the value edge1.fr.as205126.legodard.fr.

Add the domain object in the RIPE database

As all the other objects we created before, you have to login to the RIPE website, and go to the create object section.

Then in the famous list, select the domain item.

It ask you the prefix and the name servers.

The name servers is the same as Cloudflare gives you when registering your zone.

Once the fields filled, you have the reverse zone showing, compare if it is correct with your zone on Cloudflare. If not, copy this value and create a new zone on CF.

If everything is correct, you can fill the contact fields with your person object.

Conclusion

To see your rDNS works, you will have to wait at least a day, on a VPS it was 5-6h, and for my home ISP 19h.

Now, you know how to configure rDNS and how it works under the hood.