We only go into the requirements of the Denic (.de domains) here. If there are other requirements for other Top Level Domains, we will continue this articel if necessary.
To set up a nameserver you need 2 nameservers with 2 different IP's.
What is not allowed?
- To register the nameservers, not only one IPv4 address may be entered twice
- There must be at least 1 IPv4 address, therefore 2 IPv6 addresses are not allowed
What is allowed?
- You don't have to use 2 IPv4 addresses, you may also use 1 IPv4 + 1 IPv6
- 2 IPv4 addresses are allowed, IPv6 is not a requirement
- It's possible, if you want to use only one nameserver, to store it with 2 IP addresses, with 2 different names like ns1.xyz.de and ns2.xyz.de (if it makes no more sense to use 2 name servers, so that the name resolution of the domain remains redundant, you have to decide for yourself)