User-Defined Chains
The filter table has three permanent, built-in chains: INPUT, OUTPUT, and FORWARD. iptables enables you to define chains of your own, called user-defined chains. These user-defined chains are treated as rule targets—that is, based on the set of matches specified in a rule, the target can branch off or jump to a user-defined chain. Rather than the packet being accepted or dropped, control is passed to the user-defined chain to perform more specific match tests relative to packets matching the branch rule. After the user-defined chain is traversed, control returns to the calling chain, and matching continues from the next rule in the calling chain unless the user-defined chain matched and took action on the packet.
Get Linux Firewalls, Third Edition now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
