====== DNS ======
Instalando o bind
<code bash>
root@ns1:~# aptitude install bind9 bind9utils
</code>

Arquivo de zonas
<code bash>
root@ns1:~# cat /etc/bind/named.conf.local 
//
// Do any local configuration here
//

// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";

zone "exemplo.org" {
	type master;
	file "db_exemplo";
};

zone "100.51.198.in-addr.arpa" {
	type master;
	file "db_reverso";
};
</code>

Zona direta:
<code bash>
root@ns1:~# cat /var/cache/bind/db_exemplo
$TTL	1D
@	IN	SOA	ns1.exemplo.org.	root.ns1.exemplo.org. (
		2016061601	;Serial
		3H		;Refresh
		1H		;Retry
		24H		;Expire
		24H	)	;Negative Cache TTL

;
@	IN	NS	ns1.exemplo.org.
@	IN	MX	5 mail.exemplo.org.
;
gateway		IN	A	198.51.100.254
ns1		IN	A	198.51.100.200
ldap		IN	A	198.51.100.250
mail		IN	A	198.51.100.240
smtp	IN	CNAME	mail.exemplo.org.
imap	IN	CNAME	mail.exemplo.org.
</code>

Zona reversa:
<code bash>
root@ns1:~# cat /var/cache/bind/db_reverso
$TTL	1D
@	IN	SOA	ns1.exemplo.org.	root.ns1.exemplo.org. (
		2016061601	;Serial
		3H		;Refresh
		1H		;Retry
		24H		;Expire
		24H	 )	;Negative Cache TTL

;
@	IN	NS	ns1.exemplo.org.
;
254	IN	PTR	gateway.exemplo.org.
240	IN	PTR	mail.exemplo.org.
200	IN	PTR	ns1.exemplo.org.
</code>

Modificando o resolv.conf:
<code bash>
root@ns1:~# cat /etc/resolv.conf 
nameserver 127.0.0.1
</code>

<code bash>
root@ns1:~# chattr +i /etc/resolv.conf 
</code>

Reiniciando o bind e testando a resolução de nomes:
<code bash>
root@ns1:~# systemctl restart bind9
</code>

<code bash>
root@ns1:~# host -a exemplo.org
Trying "exemplo.org"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31538
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 2

;; QUESTION SECTION:
;exemplo.org.			IN	ANY

;; ANSWER SECTION:
exemplo.org.		86400	IN	SOA	ns1.exemplo.org. root.ns1.exemplo.org. 2016061601 10800 3600 86400 86400
exemplo.org.		86400	IN	NS	ns1.exemplo.org.
exemplo.org.		86400	IN	MX	5 mail.exemplo.org.

;; ADDITIONAL SECTION:
ns1.exemplo.org.	86400	IN	A	198.51.100.200
mail.exemplo.org.	86400	IN	A	198.51.100.240
</code>