[jffry]

I'm not Requestbin's creator so I don't know. A simple nslookup or curl does work for me, with my system's DNS servers set to Cloudflare (1.1.1.1) or Google (8.8.8.8)

It looks like Vodafone (I assume this is your ISP) DNS servers aren't properly resolving the name for some reason. You could try bypassing it with dig, and directly ask a different DNS server to resolve it:

  dig @1.1.1.1 A whatever.a54c4d391bad1b48ebc3.d.requestbin.net

[philh]

Thanks! Yeah, `dig` with no DNS gives me a SERVFAIL but `dig @1.1.1.1` works.

My ISP isn't Vodafone directly (I take it you think that because 83.146.21.6 belongs to them?) but might be a Vodafone reseller or something.

[jffry]

Yeah, I assumed since you were querying their DNS that you were a client, but makes sense it might be repackaged to other ISPs.