Just checked that host, nslookup, dig use /etc/hosts when tailscale is down:
erik@jojda:~$ grep -w nas /etc/hosts
192.168.1.65 nas
erik@jojda:~$ host nas
nas has address 192.168.1.65
Host nas not found: 3(NXDOMAIN)
erik@jojda:~$ nslookup nas
Server: 127.0.0.53
Address: 127.0.0.53#53
Non-authoritative answer:
Name: nas
Address: 192.168.1.65
erik@jojda:~$ dig nas
; <<>> DiG 9.16.6-Ubuntu <<>> nas
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21299
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;nas. IN A
;; ANSWER SECTION:
nas. 0 IN A 192.168.1.65
;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon Dec 07 19:47:19 PST 2020
;; MSG SIZE rcvd: 48
Now with tailscale up:
erik@jojda:~$ host nas
Host nas not found: 3(NXDOMAIN)
erik@jojda:~$ nslookup nas
Server: 100.100.100.100
Address: 100.100.100.100#53
** server can't find nas: NXDOMAIN
erik@jojda:~$ dig nas
; <<>> DiG 9.16.6-Ubuntu <<>> nas
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 33945
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;nas. IN A
;; AUTHORITY SECTION:
. 85726 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2020120702 1800 900 604800 86400
;; Query time: 28 msec
;; SERVER: 100.100.100.100#53(100.100.100.100)
;; WHEN: Mon Dec 07 19:46:26 PST 2020
;; MSG SIZE rcvd: 107