DNS (DomainNameServices) is the part of internet that translates hostnames into IP-addresses,
thus separating the logical structure (meaningfull URL’s) from the physical
structure (where systems are located in the network). DNS has a hierarchical
structure.
A DNS server holds hosts from its own domain (zone) and addresses of
DNS-servers in directly underlying domains, this can be repeated a number of
times thus covering the whole internet. The 15 Root domainservers are one of
the weak spots of the network, disabling few root domain servers causes an
overload on the remaining servers.
The program for DNS services is bind. A DNS server keeps all found mapping in
cache until the TTL(TimeToLive) of the DNS entry has passed.
Secondary DNS servers are replicas of a primary server. The replication
process is called zone transfer.
Reverse lookup (IP-address -> hostname) returns hostname and reverse
address from the Rootdomain in-addr.arpa;
- host 195.12.1.38
- 38.1.121.195.in-addr.arpa domain name pointer ns3.wxs.nl
- bind
- Application for providing Domain Name Services
- named.conf
named.boot - Configuration file for bind, may vary. Defined wich zone’s and
networks are provided by this server
Databases
- named.ca
- Holds the root servers mapping. Named.ca is loaded into the cache
upon startup. - named.<host>
- Hold the mapping for the <host> domain. named.local must exist
to be able to resolve 127.0.0.1 - <domain>.zone
- Zone file for domain, the name is defined in the named.conf file
- 10.in-addr.arpa
- Zone file for network, the name is defined in the named.conf file
Records
- @
- First meaningfull character, it represents the domainname from the
configuration file (named.conf or named.boot) - SOA
- Holds local hostname, email adres of local system manager (where @ is
replaced by .) and timers and defaults for the zone. - NS
- Nameserver for this domain
- MX
- Mailserver for this domain
- A
- A host in this domain
- CNAME
- Alias for a host in this domain
- <hostname>
- Host in zone, if there is no . (dot) after <hostname> the
default domain is added.
Usefull commands
- ipv6calc –in ipv6addr –out revnibbles.arpa 2001:4b98:41::d946:bc7c:124
- Returns address in the format to use in reverse DNS zonefiles (PTR)