Computer Network Security

5Using Firewalls

This chapter will focus on the following topics:

• – the role a firewall plays;
• – the types of firewalls:
  • - NAT firewall,
  • - packet-filtering firewall,
  • - stateful firewall,
  • - application firewall;
• – setting up a firewall;
• – different firewall strategies;
• – ACL-based firewalls:
  • - IPv4 ACLs,
  • - IPv6 ACLs;
• – zone-based firewalls:
  • - the types of security zones in a network,
  • - rules applied to inter-zone traffic,
  • - configuring a ZFW.

5.1. Introducing firewalls

A firewall is a software or hardware system put in place between a reliable network and an unreliable one. The main purpose of putting in place a firewall is to filter out and prevent unwanted traffic from crossing the firewall barrier. In order to do this, a firewall must comply with the following recommendations:

• – it must be resistant to attacks;
• – it must be the only transit point between two networks;
• – it must ensure that the organization’s access control strategy is applied.

5.2. Types of firewalls

There are different kinds of firewalls. Some of these are:

• – NAT firewall: this hides a private IP address by translating it into a public IP address;
• – packet-filtering firewall: this makes it possible to filter packets from Layers 3 or 4 of the OSI model. This kind of firewall is simple to configure but is also vulnerable to identity-theft attacks;
• – stateful firewall: this carries out the same function as a packet-filtering firewall and also keeps track of the state of network connections (i.e. ...