NotesByLex

Red Hat System Administration III - Unit 15 - Caching Only DNS Server

Lex Toumbourou ·

Linux

DNS General

  • Authoritative
    • Master - contains original zone data. A "primary" nameserver
    • Slave - backup server. Copy of zone data.
  • Non-authoritative / recursive nameservers
    • Caching-only - used for lookups, not authoritative for anything cept trivial data
  • Enable 53 for TCP and UDP for DNS

Bind

  • Package bind

  • config = /etc/named.conf

    > vi /etc/named.conf
+ listen-on port 53 { any; };
+ listen-on-v6 port 53 { any; };
+ allow-query     { 192.168.0.0/24; };
+ dnssec-validation no;  // stops spoofing DNS

  • Dump contents of caching db

    > rndc dumpdb --cache
> cat /var/named/data/cache_dump.db

DNS Lookups

  • Stub resolve sends query to client in /etc/resolv.conf
  • If nameserver is authoritative, send authoritative answer to client
    • A - forward lookup (name to ipv4 address)
    • AAAA - forward lookup (name to ipv6 address)
    • PTR - reverse record
    • MX - mail exchange
    • SOA - start of authoritity
    • CNAME - alias (canonical name)
  • Use dig for troubleshooting
    > dig www.example.com

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6 <<>> www.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 52706
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;www.example.com.       IN  A

;; AUTHORITY SECTION:
example.com.        60  IN  SOA instructor.example.com. root.instructor.example.com. 2010091500 3600 300 604800 60

;; Query time: 0 msec
;; SERVER: 192.168.0.254#53(192.168.0.254)
;; WHEN: Thu Aug  8 11:29:47 2013
;; MSG SIZE  rcvd: 85