could be on completely different machines/subnets.
These days a lot of ISP's Anycast their DNS Servers so you have (as a /32) in say Auckland, Wellington, Christchurch the same IP Address. This means 184.108.40.206/32 is a completely different subnet as 220.127.116.11/32.
I'm not saying TelstraClear do it this way but quite a few do.
Yeah, that's why I said it was a simplification. The fact that both DNS servers went down at once suggests it doesn't operate this way.
I don't think Telstraclear are even anycasting their primary DNS. But I could be wrong. From past memory 18.104.22.168 was in Wellington, and 203.97. servers were in Auckland, from Christchurch.