Pdns: AXFR problem - Pdns Authoritative server

[mSys-mislav]

• Program: Authoritative
• Issue type: Bug report

Short description

AXFR in new Pdns Authoritative server is creating empty records (NULL) when transferring zones from another PDNS server or from bind zone.

Environment

• Operating system: Debian 9
• Software version: PowerDNS Authoritative Server 4.1.0-rc3
• Software source: powerdns repository (http://repo.powerdns.com/debian stretch-auth-41 main)

Steps to reproduce

1. Install Debian 9
2. Follow instructions on how to add new pdns repository, install pdns (with mysql backend)
3. Enter mysql, execute the following query:
   https://doc.powerdns.com/authoritative/migration.html#using-axfr-to-a-slave-capable-backend
   INSERT INTO domains (name,type,master) VALUES ('example.net', 'SLAVE', '198.51.100.101');
   (change the example.net to your domain name and IP to your master IP)
4. Wait a minute until AXFR is over. Check records table and you will see empty additional records.

Expected behaviour

I would expect no additional records being added after AXFR, just like AXFR was working fine in previous pdns authoritative server.

Actual behaviour

On AXFR, as explained, there are few additional empty records added, with type, content, etc - NULL.

Other information

I've tried to ask community, but specific answer there. One person mentioned this could be DNSSEC related? Is it? Or is it really a bug? Here is the link to that topic:
https://mailman.powerdns.com/pipermail/pdns-users/2017-November/025055.html

as mentioned there, there is no difference if I do AXFR from old 3.1. pdns server version or if master is bind-alike, same thing occurs.

If some addition logs are needed, let me know.

[ahupowerdns]

are you experiencing problems from the NULL entries? They are related to Empty Non Terminals, a DNS oddity. We have to have them.

[mSys-mislav]

Can you give some short description what are those exactly, because I can't find much on google. Currently there are no problems, but maybe in the future there will be? Thoughts? I have master with e.g. 20 records and then slave 22 records. If then slave becomes master in the future, I would need to test how these empty records are transferred to the new slave/master.

[ahupowerdns]

https://doc.powerdns.com/md/authoritative/backend-generic-sql/ has a description. https://github.com/PowerDNS/pdns/issues/127 has some context. In general, you might want to trust that we know what we are doing. The NULLs are there so we can comply with the RFCs.

[pieterlexis]

Hi @mislav-eu I think you need to read the second to last paragraph here. This explains what you are seeing.

[mSys-mislav]

@ahupowerdns @pieterlexis I apologize, but I didn't have any bad intentions here. I was only looking for some answer/details why is this exactly. I do trust you, that's why I use your program/solution, however I need to give some answer to my superiors. I wouldn't open here new report if I received there this answer. This paragraph gives all the answers I was looking for and I understand now. Thank you very much!