DNS Concept
DNS name server:
- stores the DNS records for a domain;
- uses the UDP port 53 to serve requests
Resource Records (RRs):
| Type | Description | Function |
|---|---|---|
| SOA | Start (Zone) of Authority | authoritative information about a DNS zone, - primary name server - several timers relating to refreshing the zone. |
| A | IP addresses | map hostnames to an 32-bit IPv4 address |
| AAAA | IPv6 IP addresses | map hostnames to an 128-bit Ipv6 address |
| CAA | (DNS) Certification Authority Authorization | constraining acceptable CAs for a host/domain |
| MX | mail exchangers | Maps a domain name to a list of MTA (message transfer agents) for that domain |
| NS | name servers | assign a DNS zone to use the given authoritative name servers - Used by Top level domain server - direct traffic to the authoritative Contebt Domain servers |
| CNAME | Canonical name record domain name aliases |
Alias of one name to another -> an alias for only the exact name |
| DNAME | Alias for a name and all its subnames |
TTL (Time-To-Live)
The length that a DNS record cached on the Resolving server
- an expiration time after which the results must be discarded or refreshed.
- changes to DNS records do not propagate throughout the network immediately,
- require all caches to expire and to be refreshed after the TTL.
Reverse DNS lookup
- Used when IP address is known, but do not know the associated domain name
- querying of the Domain Name System (DNS) to determine the domain name associated with an IP address
Linux local Files Related to DNS:
/etc/resolv.conf : Add or Change DNS server information
/etc/hosts : Local DNS service
/etc/named.conf: the settings for the BIND ((Berkeley Internet Name Domain) name server