Failure of an entire Top-Level Domain (TLD)is considered a low-risk probability, but it is not unheard of, and if it were to occur in a TLD, which happens to be the super-domain for all of your nameserver records, then all client domains will go dark.
No TLD redundancy:
ns1.example.comns2.example.comns3.example.comns4.example.com
I consider it a best practice to split your nameserver delegation across multiple TLDs.
TLD redundancy:
ns1.example.comns2.example.netns3.example.orgns4.example.xyz
The author's is not a consensus position. In DNS parlance, there is sometimes a debate over whether a given zone's nameservers should be in-bailiwick or out-bailiwick. The former means all NS RRs are within the same zone being served. An ...
