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nslookup

  • Check an IP of a hostname in a DNS server
  • nslookup does not include entries in /etc/hosts
# Find the IP from a hostname
nslookup "hostname"
nslookup www.google.com

# Find the hostname of a ip
nslookup "ip"
nslookup 172.217.28.4

# specify type
nslookup -type=SOA hvitoi.com # check the name server
nslookup -type=NS hvitoi.com
  • Server: is the resolver. The DNS server. Usually the modem or the router
  • Address: the ip and port of the DNS server
  • Non-authoritative answer: Means that the DNS server (modem) does not have info about the provided hostname (E.g., www.google.com), therefore it went outside on the internet to find that info
  • The DNS server does already have the info about the hostname saved in the local environment. It's NOT shown as non-authoritative answer

DNS

  • Domain Name System (DNS)
  • DNS is a system to translate a hostname to ip address and vice-versa

  • 8.8.8.8 google DNS server configured to provide DNS resolutions

  • Translation types

  • A Record: hostname to ip (forward)

  • PTR Record: ip to hostname (reverse)

  • CNAME Record: hostname to hostname

  • DNS setup

  • Master DNS

  • Secondary or slave DNS

  • Client

  • bind9 is the name of the DNS package

sudo apt install bind9
apt-get install bind9-doc
  • named is the name of the dns service
systemctl status named

  • DNS configuration files

  • /etc/bind/named.conf

  • /etc/bind/named.conf.options
  • /etc/bind/named.conf.local
  • /etc/bind/named.conf.default-zones

Name servers

  • Name servers identify your domain's location on the internet
  • You can specify the name servers for your domain. E.g., google (ns-cloud-c1.googledomains.com), azure (ns1-05.azure-dns.com)