[walrus01]

Naming major city ISP POPs by IATA airport codes is a practice that goes back to uunet/AS701 in about 1995, maybe a bit earlier, when talking about reverse DNS for public IP space. It actually predates the existence of ARIN, even.

then appending a number, so your first POP/core site in the DFW area might be DFW01, then DFW02, DFW03, and so on.

On an international scale another non-airport or IATA related method is to group by ISO standard two or three country codes and then state/province/regional internal subdivision two letter abbreviations, so something in the bay area of california might have the last part of its DNS name as sfo01.ca.us.as12345.net