Looking up local domain names with nslookup shows <host>.localdomain. Similarly, if I use nslookup and I check <host>.localdomain it resolves on both Windows and in Ubuntu to the expected value.
What is the significance of ".localdomain"? Why does it show up, why does it work, and can it be relied on? Is it specified in a standard or anything/is it OS or manufacturer specific? It seems like it's a domain equivalent of localhost, but I can't find it documented anywhere.
Example of looking up a local host:
> nslookup me-fractal
Server: setup.ubnt.com
Address: 192.168.1.1
Name: me-fractal.localdomain
Address: 192.168.1.77
Example showing localdomain actually means something:
$ nslookup testhost.localdomain
Server: 127.0.0.53
Address: 127.0.0.53#53
Non-authoritative answer:
Name: testhost.localdomain
Address: 192.168.1.198
while an arbitrary value does not resolve:
$ nslookup testhost.othervalue
Server: 127.0.0.53
Address: 127.0.0.53#53
** server can't find testhost.othervalue: NXDOMAIN
I think somewhat notably, the value does not show up in https://serverfault.com/a/937808 (or the other answers).
.localdomain: tools.ietf.org/id/draft-chapin-rfc2606bis-00.html, not sure if that went anywhere. Doesn't answer what tools are using it, but lends some credence to it being a standard. – Rubdown