DNS

Reverse Lookups

Reverse DNS

• Given an IP address, find the hostname

• some applications want to do this

• Same DNS hierarchy is used but different branch of the tree.
• For example, www.thegummibear.com should match IP 144.38.199.165. This is given as an A record in DNS as we have previously seen.

Reverse DNS

For that same example, when using reverse DNS, the special name is :

• 165.199.38.144.in-addr.arpa.

Note that this is the reverse of my IP address and a special suffix.

Reverse DNS

Reverse DNS

• Reverse DNS requires authoritative servers, just like any other zone
• Requires delegation from a higher server

Reverse DNS Steps

• Checkout IPs from system
• Configure one authoritative master
• Configure one or more authoritative slaves
• Configure registrar to delegate to authoritative servers
• Test!

Reverse DNS (Authoritative Master)

• Install bind9 (if not alread installed)
• Configure named.conf.local with authoritative zone record.
• Create zone file
• Restart named
• Check syslog for errors.

Reverse DNS (Authoritative Slave)

• Install bind9 if needed
• Configure named.conf.local with authoritative zone record.
• Restart named
• Check syslog for errors
• Check master for syslog errors
• Test system for responses
• Fix errors, until correct.

Registrar Delegation Setup

• Collect hostnames of all Authoritative servers
• Collect names of reverse DNS zone
• Send info to registrar
• Wait for registrar
• Test delegation
• Correct errors. Test.