With forward zone:


176 zone "vpn" {
177         type forward;
178         forward only;
179         forwarders { 44.0.0.8; };
180 };


[root@kai ~]# systemctl restart named
[root@kai ~]# dig sip.vpn

; <<>> DiG 9.13.3 <<>> sip.vpn
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 1329
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: a0ef2a6537d8e8733d6f96345bc511d90cebe7a1c5e3d507 (good)
;; QUESTION SECTION:
;sip.vpn.                       IN      A

;; Query time: 22 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Di Okt 16 00:16:57 CEST 2018
;; MSG SIZE  rcvd: 64

[root@kai ~]# dig vpn NS

; <<>> DiG 9.13.3 <<>> vpn NS
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37163
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: da342af47bd4365b9d8fcc0d5bc511e0bcc79e16382d9f72 (good)
;; QUESTION SECTION:
;vpn.                           IN      NS

;; ANSWER SECTION:
vpn.                    38400   IN      NS      nasuada.vpn.

;; ADDITIONAL SECTION:
nasuada.vpn.            38400   IN      A       44.0.0.8

;; Query time: 23 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Di Okt 16 00:17:04 CEST 2018
;; MSG SIZE  rcvd: 98

[root@kai ~]# dig sip.vpn

; <<>> DiG 9.13.3 <<>> sip.vpn
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10431
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: dce9dd303730d4b8996d71045bc511e3840f8bfa1362b060 (good)
;; QUESTION SECTION:
;sip.vpn.                       IN      A

;; ANSWER SECTION:
sip.vpn.                38400   IN      A       44.0.0.80

;; Query time: 25 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Di Okt 16 00:17:07 CEST 2018
;; MSG SIZE  rcvd: 80

[root@kai ~]#







With static-stub:



182 zone "vpn" {
183     type static-stub;
184     //server-names { nasuada.vpn; };
185     server-addresses { 44.0.0.8; };
186 };


[root@kai ~]# systemctl restart named
[root@kai ~]# dig sip.vpn

; <<>> DiG 9.13.3 <<>> sip.vpn
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 20155
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: a139de1b9ae23867c3046a765bc512358f33bf268fd725d7 (good)
;; QUESTION SECTION:
;sip.vpn.                       IN      A

;; Query time: 27 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Di Okt 16 00:18:29 CEST 2018
;; MSG SIZE  rcvd: 64

[root@kai ~]#









In all the SERVFAIL and NXDOMAIN cases, the server at 44.0.0.8 doesn't even seem to get a query according to tcpdump