ZyXEL Communications P-661H Series - Manual (Page 15)

P-661H/HW Series User’s Guide
Table of Contents 15
Chapter 8
Firewalls................................................................................................................ 145
8.1 Firewall Overview ............................................................................................145
8.2 Types of Firewalls ............................................................................................145
8.2.1 Packet Filtering Firewalls ........................................................................145
8.2.2 Application-level Firewalls ......................................................................146
8.2.3 Stateful Inspection Firewalls ...................................................................146
8.3 Introduction to ZyXEL’s Firewall .......................................................................146
8.3.1 Denial of Service Attacks ........................................................................147
8.4 Denial of Service ..............................................................................................147
8.4.1 Basics .....................................................................................................147
8.4.2 Types of DoS Attacks .............................................................................148
8.4.2.1 ICMP Vulnerability ........................................................................150
8.4.2.2 Illegal Commands (NetBIOS and SMTP) ......................................150
8.4.2.3 Traceroute .....................................................................................151
8.5 Stateful Inspection ............................................................................................151
8.5.1 Stateful Inspection Process ....................................................................152
8.5.2 Stateful Inspection and the ZyXEL Device ..............................................152
8.5.3 TCP Security ...........................................................................................153
8.5.4 UDP/ICMP Security ................................................................................153
8.5.5 Upper Layer Protocols ............................................................................154
8.6 Guidelines for Enhancing Security with Your Firewall ......................................154
8.6.1 Security In General .................................................................................154
8.7 Packet Filtering Vs Firewall ..............................................................................155
8.7.1 Packet Filtering: ......................................................................................155
8.7.1.1 When To Use Filtering ...................................................................156
8.7.2 Firewall ...................................................................................................156
8.7.2.1 When To Use The Firewall ............................................................156
Chapter 9
Firewall Configuration ......................................................................................... 157
9.1 Access Methods ...............................................................................................157
9.2 Firewall Policies Overview ...............................................................................157
9.3 Rule Logic Overview ........................................................................................158
9.3.1 Rule Checklist .........................................................................................158
9.3.2 Security Ramifications ............................................................................158
9.3.3 Key Fields For Configuring Rules ...........................................................159
9.3.3.1 Action ............................................................................................159
9.3.3.2 Service ..........................................................................................159
9.3.3.3 Source Address .............................................................................159
9.3.3.4 Destination Address ......................................................................159
9.4 Connection Direction ........................................................................................159
9.4.1 LAN to WAN Rules .................................................................................160