On Fri, 22 Mar 2019 14:38:03 +0100,
Roby , in
 wrote:

>  But I can't verify which DNS uses the RPI3 because I don't have the
>  nslookup command available

Superceded by host (and/or dig):

% host 8.8.8.8
8.8.8.8.in-addr.arpa domain name pointer google-public-dns-a.google.com.

% dig 8.8.8.8

; > DiG 9.11.5-P4-1-Debian > 8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 28905
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;8.8.8.8.   IN A

;; AUTHORITY SECTION:
.   1425 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2019032501 1800 900
604800 86400

;; Query time: 8 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Mar 25 14:36:34 EDT 2019
;; MSG SIZE  rcvd: 111

I'm running dnsmasq locally to provide a caching dns service, which is
why it identifies as localhost as the server.

Oh, and usually when you encounter a 404 error in debian-style
repository, it is because your package list is out of sync with the
remote provider. apt-get update should cure that issue.

--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

--- SoupGate-Win32 v1.05