PIX acts like a proxy server

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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.