Nsupdate with empty A record

#1

In order to mitigate the ongoing loss of records I wrote a Script which check for losses.
I want to use the API to recreate the domains. Sadly the v4 A Record gets lost. In order to recreate it I need to issue the update command with an empty A record so that the ip will be updated on update.

This seems not to be possible,

nsupdate <<EOF
server ns1.dynv6.com
zone example.com
update add v4.example.com 0 A
key hmac-sha1:[…]
send
EOF

which throws the error

could not read rdata
syntax error

Does anyone have a working example? is there a special string which needs to be used ?

Thanks in advance!

#2

The code example in the official website documentation are just fine.
https://dynv6.com/docs/apis#dns-update
Delete first, then add.

#3

I don’t think that you understand the problem. I never doubted that the example works.
Creating a new Record is not the problem. Creating a new record which is empty thus creating a dynamic record is the problem.

update add v4.example.com 0 A “here needs to be a valid ip”

but in order to create an A record which gets update on ip change this needs to be empty which is not possible with this code snippet.

Is there a special string or IP which needs to be used?

#4

There is no point in creating an empty A record. If you don’t have an IP address, you don’t need a record. Why should a DNS server remember something like this? If you have a dynamic address, take the current one and update it when it changes.

#5

Sure at a normal DNS Server an A Record without an IP makes not sense.
When I create an empty A Record here there will be created a dynamically updated record.

And yes at this point of time I update the IP via the script but I just want to know if it is possible to create a record at dynv6 with nsupdate which will be dynamically updated when the ipv4 changes.

Thanks

#6

You don’t really understand ‘dynamic’. It means connecting an IP dynamically assigned by your ISP to a (sub) domain. If there is a change, it is passed on very quickly (TTL usually 1 to 5 minutes). But you are responsible for the update, because only you know when your ISP has assigned you a new IP. How is a DNS server supposed to determine that?

#7

This is the dynv6 board, isn’t it? The whole purpose of this service is dynamic DNS. Why should I update the IP manually when this service does is automatically?

I honestly think that we are talking past each other.

Let me ask differently:
Is it possible to create an A Record with the “not set”-flag as in the first row in the picture below via nsupdate?

Bildschirmfoto 2022-01-17 um 20.59.20
Bildschirmfoto 2022-01-17 um 20.59.202308×140 37.2 KB

Best regards

#8

I am very sorry, my mistake.

I didn’t think it was about an A entry for a subdomain. Although you can create an empty entry (not set) with dynv6, you can’t do that with nsupdate. nsupdate checks the parameters and does not allow an empty RDATA field.

I don’t think that can be done with standard tools. It’s a special ‘dynv6’ thing that this is possible. They probably replace the empty entry internally with the A entry of the main domain. I don’t know if there is another option besides the web interface.

#9

I looked around and tried a bit. You can use the REST API for dynv6. There you can specify an empty string for the data field when adding a new record (or simply omit the field). This leads to the desired result.

#10

FYI:

   curl -sS --fail \
   -H "Authorization: Bearer <YourToken>" \
   -H "Content-Type: application/json" \
   -H "Accept: application/json" \
   --data '{"name": "wantedsubdomain", "type": "A"}' \
   https://dynv6.com/api/v2/zones/<zoneID>/records

Replace <YourToken> with your HTTP token and <ZoneID> with your zone ID. You get your zone(s) and ID(s) with:

   curl -sS --fail \
   -H "Authorization: Bearer <YourToken>" \
   -H "Content-Type: application/json" \
   -H "Accept: application/json" \
   https://dynv6.com/api/v2/zones | jq