ZyXEL Communications G.SHDSL.bis 4-port Security Gateway P-793H User Manual page 14

Table of Contents
Part III: Security and Advanced Setup ................................................115
Chapter 8
Firewalls................................................................................................................................. 117
8.1 Firewall Overview ...............................................................................................................117
8.2 Types of Firewalls ...............................................................................................................117
8.2.1 Packet Filtering Firewalls ..........................................................................................117
8.2.2 Application-level Firewalls .........................................................................................118
8.2.3 Stateful Inspection Firewalls ......................................................................................118
8.3 Introduction to ZyXEL's Firewall .........................................................................................118
8.3.1 Denial of Service Attacks ..........................................................................................119
8.4 Denial of Service ................................................................................................................119
8.4.1 Basics ........................................................................................................................119
8.4.2 Types of DoS Attacks ................................................................................................119
8.5 Stateful Inspection ............................................................................................................. 122
8.5.1 Stateful Inspection Process ...................................................................................... 123
8.5.2 Stateful Inspection and the ZyXEL Device ............................................................... 124
8.5.3 TCP Security ............................................................................................................ 124
8.5.4 UDP/ICMP Security .................................................................................................. 125
8.5.5 Upper Layer Protocols ............................................................................................. 125
8.6 Guidelines for Enhancing Security with Your Firewall ....................................................... 126
8.6.1 Security In General .................................................................................................. 126
8.7 Packet Filtering vs. Firewall ............................................................................................... 127
8.7.1 Packet Filtering ........................................................................................................ 127
8.7.2 Firewall ..................................................................................................................... 127
Chapter 9
Firewall Configuration .......................................................................................................... 129
9.1 Access Methods ................................................................................................................ 129
9.2 Firewall Policies Overview ................................................................................................. 129
9.3 Rule Logic Overview .......................................................................................................... 130
9.3.1 Rule Checklist .......................................................................................................... 130
9.3.2 Security Ramifications .............................................................................................. 130
9.3.3 Key Fields For Configuring Rules ............................................................................ 131
9.4 Connection Direction ......................................................................................................... 131
9.4.1 LAN to WAN Rules ................................................................................................... 132
9.4.2 Alerts ........................................................................................................................ 132
9.5 Triangle Route ................................................................................................................... 132
9.5.1 The "Triangle Route" Problem .................................................................................. 132
9.5.2 Solving the "Triangle Route" Problem ...................................................................... 133
9.6 General Firewall Policy ...................................................................................................... 133
9.7 Firewall Rules Summary ................................................................................................... 135
9.7.1 Configuring Firewall Rules ..................................................................................... 136
14
P-793H User's Guide