ZyXEL Communications G.SHDSL.bis 4-port Security Gateway P-793H - Manual (Page 14)

P-793H User’s Guide
14 Table of Contents
7.6.1 Address Mapping Rule Edit ...................................................................116
Chapter 8
Firewalls................................................................................................................ 119
8.1 Firewall Overview .............................................................................................119
8.2 Types of Firewalls ............................................................................................119
8.2.1 Packet Filtering Firewalls ........................................................................119
8.2.2 Application-level Firewalls ......................................................................120
8.2.3 Stateful Inspection Firewalls ...................................................................120
8.3 Introduction to ZyXEL’s Firewall .......................................................................120
8.3.1 Denial of Service Attacks ........................................................................121
8.4 Denial of Service ..............................................................................................121
8.4.1 Basics .....................................................................................................121
8.4.2 Types of DoS Attacks .............................................................................122
8.4.2.1 ICMP Vulnerability .........................................................................124
8.4.2.2 Illegal Commands (NetBIOS and SMTP) ......................................124
8.4.2.3 Traceroute .....................................................................................125
8.5 Stateful Inspection ............................................................................................125
8.5.1 Stateful Inspection Process ....................................................................126
8.5.2 Stateful Inspection and the ZyXEL Device ..............................................126
8.5.3 TCP Security ...........................................................................................127
8.5.4 UDP/ICMP Security ................................................................................127
8.5.5 Upper Layer Protocols ............................................................................128
8.6 Guidelines for Enhancing Security with Your Firewall ......................................128
8.6.1 Security In General .................................................................................128
8.7 Packet Filtering vs. Firewall .............................................................................129
8.7.1 Packet Filtering .......................................................................................129
8.7.1.1 When To Use Filtering ...................................................................130
8.7.2 Firewall ...................................................................................................130
8.7.2.1 When To Use The Firewall ............................................................130
Chapter 9
Firewall Configuration ......................................................................................... 131
9.1 Access Methods ...............................................................................................131
9.2 Firewall Policies Overview ...............................................................................131
9.3 Rule Logic Overview ........................................................................................132
9.3.1 Rule Checklist .........................................................................................132
9.3.2 Security Ramifications ............................................................................132
9.3.3 Key Fields For Configuring Rules ...........................................................133
9.3.3.1 Action ............................................................................................133
9.3.3.2 Service ..........................................................................................133
9.3.3.3 Source Address .............................................................................133
9.3.3.4 Destination Address ......................................................................133