DNS servers also allow reverse lookup; given an IP address 128.112.169.4, it is reversed into a text string 4.169.112.128.in-addr.

arpa and looked up using DNS PTR records (which form a hierarchy of domains analogous to that for the address domain hierarchy).

Suppose you want to authenticate the sender of a packet based on its host name and are confident that the source IP address is genuine.Explain the insecurity in converting the source address to a name as above and then comparing this name to a given list of trusted hosts.

Whose DNS servers would you be trusting?