Superior to Unix and other router firewalls

148 As the PIX was designed with only one purpose in mind, that of securing a private network by both filtering traffic and establishing secure links across an unprotected Internet, it is an excellent place to establish logging controls on the network. Further, the PIX machine is a fine encryption device, protecting valuable communication with tried and true cryptographic techniques.

9.2.2.3 Single point of controlfailure

When network trouble is at hand, a clear delineation between the outside world and ones local world is an immense asset. By using a single unit to handle the networks entire firewalling needs, the network coordinator has a clear starting point for troubleshooting. The PIX provides such an architecture. By having a single unit handle all network traffic in this manner, equipment malfunction and software misconfiguration could cause a great amount of havoc in one fell swoop. But Cisco has anticipated this problem with a fail-over, hot-standby mode, whereby two units can be configured in parallel. Should some fault occur to one of the units, the other can support the firewall by maintaining operation transparently.

9.2.2.4 Dynamic address translation

The dynamic translation feature, which allows users to pick up a free address from the Internet pool whenever they need one, does more than just allow many people to share a few NIC registered addresses. It also provides adaptive security to the hosts using the internal addresses. The PIX unit has two interfaces, one for the exterior network and one for the interior one. Because of this, the internal address range is hidden by translating the internal address into the dynamic pool of addresses for Internet exchange. This method provides a high level of security because a threat is much less likely when an attacker doesnt know the architecture, network range, or setup of the internal network

9.2.2.5 PIX acts like a proxy server

Unix-based proxy servers are commonplace in todays world, and most of them serve their function well. Proxy servers do essentially what the PIX firewall was engineered to do: they hide a machine or a network of machines from the outside world by masquerading as the client in network conversations with unknown or unverifiable parties. The PIX is more robust than the standard proxy servers because it provides a quick session bypass once the authenticated parties have shaken hands. Traditional proxy servers maintain state information for the duration of the session, and handle their packet control at the top of the protocol stack. Moreover, because software-driven proxy servers perform packet filtering, they prevent the use of almost all the VPN solutions on the market today.

9.2.2.6 Ease of configuration and maintenance

For the most part, the PIX is very easy to handle in everyday use. Once the configuration is applied and tested, it handles its job silently and without complaint. As is popular in todays world, to further assist the network coordinators that will be installing the device, Cisco has made an HTML front end for configuration. There is of course the old standby option of the command-line-driven interface, which could be used by those more familiar with Ciscos prevalent IOS software. 149

9.2.2.7 High-speed access

For those with ultra-high-capacity lines, such as fractional or full DS3s T3s, the PIX, with its two 100-megabit Ethernet cards, can easily handle a significant amount of Internet traffic. Although we wouldnt recommend piping a T3s full load of traffic through only one machine, the fact that the capacity is there is quite a benefit.

9.2.2.8 Links

By using an additional card that comes separately, the PIX firewall can be used to create an encrypted channel between itself and another such unit somewhere out on the public side of the PIX. This private link encryption feature gives the PIX firewall its most tremendous benefit: it lets organizations link private Internets securely using the public networks, with very simple configuration. Thats what this book is all about. One slight disadvantage is that the PIX firewall supports only IP traffic. We suppose this could be considered an advantage as well.

9.2.3 Limitations of the PIX Firewall

Even though the PIX is a nearly complete solution to the development of a virtually private network, it does have some drawbacks in terms of maintenance, network address translation limits, and price.

9.2.3.1 Hardware solution

Hardware can be tricky if mismanaged, difficult to debug if misconfigured, and hard to replace quickly if broken. Hardware like the PIX is provided by only one vendor, and you cant be sure what will happen to the vendor in the future.

9.2.3.2 Dynamic address use

There is a limited pool of addresses that the PIX can assign to hosts on your internal network that want to communicate with the outside. Cisco sells a few different varieties of the product, allowing for 32, 256, or 1024 sessions simultaneously. Remember that one user could be using many different sessions at once, so there is a definite limit on how much a PIX can handle when its connected to a huge network.

9.2.3.3 Budgetary considerations

A whole squadron of Cisco PIX units might be prohibitively expensive to widely distribute across your network. The PIX firewall has a suggested retail price in the tens of thousands of dollars, and the encryption cards required to create VPN tunnels go for a few thousand each.

9.2.3.4 Maintenance

As with any new equipment, you have to consider the need for ongoing maintenance and growth. The PIX firewall, which may be initially easy to configure, could grow to have a complex configuration even if there are no other firewalls providing a similar function. The persons in charge of coordinating network activity need to establish a plan for how traffic needs to be restricted, and to which networks these restrictions apply. Subtle mistakes in the configuration could lead to potentially large security holes.