DNS config files, Zone file example and DNS Resource Types

The original dns config file. This file is the parent configuration file, we can include other conf file inside this one.


The host configuration file


When there is a change made to the dns config file, the dns server needs to be restarted. To restart the dns server

sudo /etc/init.d/named restart
sudo service named restart

DNS debug tools

ping codexpedia.com
nslookup codexpedia.com
dig codexpedia.com

DNS Zone file example

$ORIGIN example.com.     ; designates the start of this zone file in the namespace
$TTL 1h                  ; default expiration time of all resource records without their own TTL value
example.com.  IN  SOA  ns.example.com. username.example.com. (
              2007120710 ; serial number of this zone file
              1d         ; slave refresh (1 day)
              2h         ; slave retry time in case of a problem (2 hours)
              4w         ; slave expiration time (4 weeks)
              1h         ; maximum caching time in case of failed lookups (1 hour)
example.com.  NS    ns                    ; ns.example.com is a nameserver for example.com
example.com.  NS    ns.somewhere.example. ; ns.somewhere.example is a backup nameserver for example.com
example.com.  MX    10 mail.example.com.  ; mail.example.com is the mailserver for example.com
@             MX    20 mail2.example.com. ; equivalent to above line, "@" represents zone origin
@             MX    50 mail3              ; equivalent to above line, but using a relative host name
example.com.  A             ; IPv4 address for example.com
              AAAA  2001:db8:10::1        ; IPv6 address for example.com
ns            A             ; IPv4 address for ns.example.com
              AAAA  2001:db8:10::2        ; IPv6 address for ns.example.com
www           CNAME example.com.          ; www.example.com is an alias for example.com
wwwtest       CNAME www                   ; wwwtest.example.com is another alias for www.example.com
mail          A             ; IPv4 address for mail.example.com,
                                          ;  any MX record host must be an address record
                                          ; as explained in RFC 2181 (section 10.3)
mail2         A             ; IPv4 address for mail2.example.com
mail3         A             ; IPv4 address for mail3.example.com
mysite.example.com.	A		  ; Ipv4 address for mysite.example.com

A zone file is referenced by the dns configuration named.conf or any other conf files included in named.conf.For example, assume the zone file is located at /var/named/db.example.com, the dns conf file need to have this

zone "example.com" { type master; file "/var/named/db.example.com"; };

DNS Resource Records

A		IPv4 Address record. An IPv4 address for a host.
AAAA	IPv6 Address record. An IPv6 address for a host. Current IETF recommendation for IPv6 forward-mapped zones.
A6		Experimental. Forward mapping of IPv6 addresses. An IP address for a host within the zone.
AFSDB	Location of AFS servers. Experimental - special apps only.
CNAME	Canonical Name. An alias name for a host.
DNAME	Experimental. Delegation of reverse addresses (primarily IPv6).
DNSKEY	DNSSEC.bis. DNS public key RR.
DS		DNSSEC.bis. Delegated Signer RR.
HINFO	Host Information - optional text data about a host.
ISDN	ISDN address. Experimental = special applications only.
KEY		Public key associated with a DNS name.
LOC		Stores GPS data. Experimental - widely used.
MX		Mail Exchanger. A preference value and the host name for a mail server/exchanger that will service this zone. RFC 974 defines valid names.
NAPTR	Naming Authority Pointer Record. Gross misnomer. General purpose definition of rule set to be used by applications e.g. VoIP
NS		Name Server. Defines the authoritative name server(s) for the domain (defined by the SOA record) or the subdomain.
NSEC	DNSSEC.bis. Next Secure record. Ssed to provide proof of non-existence of a name.
NXT		Domain record type. Obsolete use NSEC.
PTR		IP address (IPv4 or IPv6) to host. Used in reverse maps.
RP		Information about responsible person. Experimental - special apps only.
RRSIG	DNSSEC.bis. Signed RRset.
RT		Through-route binding. Experimental - special apps only.
SIG		DNSSEC. Obsolete use RRSIG. SIG(0) is used as a special meta RR in DDNS and zone transfer security.
SOA		Start of Authority. Defines the zone name, an e-mail contact and various time and refresh values applicable to the zone.
SPF		Sender Policy Framework (v1). Defines the servers which are authorized to send mail for a domain. Its primary function is to prevent identity theft by spammers.
SRV		Defines services available in the zone, for example, ldap, http etc..
TXT		Text information associated with a name. The SPF record should be defined using a TXT record and may (as of April 2006) be defined using an SPF RR. DKIM (RFC 4871 also makes use of the TXT RR for authenticaing email. How to define DKIM/ADSP RRs.
WKS		Well Known Services. Deprecated in favour of SRV.
X25		X.25 address. Experimental - special apps only.

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