Linux Firewalls, Third Edition

Appendix D. Glossary

This glossary defines terms and acronyms used in the book. Multiword terms are alphabetized on the major noun in the term, followed by a comma and the rest of the term.

ACCEPT

A firewall-filtering rule decision to pass a packet through to its next destination.

accept-everything-by-default policy

A policy that accepts all packets that don't match a firewall rule in the chain. Therefore, most firewall rules are DENY rules defining the exceptions to the default accept policy.

ACK

The TCP flag that acknowledges receipt of a previously received TCP segment.

application-level gateway

Often referred to as ALG, an application-level (or layer) gateway is an overloaded term. In firewall terms, ALG often refers to application-specific support ...