IPtables - Set Default Policy

IPtables is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains. Each chain is a list of rules which can match a set of packets. A firewall rule specifies a criteria for a packet, and a target (what to do with the packet that matches a criteria: one of the special values: ACCEPT or DROP). If the packet does not match, the next rule in the chain is examined; if it does match, then rule that specified by the value of the target is used; if a packet matches no rules, then the default policy is applied.

Here you can set the packages management rules applied in the case if all other rules do not match: select one of the special values: ACCEPT or DROP both for incoming packets (Input chain) and outgoing packets (Output chain). Click 'OK' to save changes.