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 18.104.22.168/32 is a completely different subnet as 22.214.171.124/32.
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 126.96.36.199 was in Wellington, and 203.97. servers were in Auckland, from Christchurch.