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8. Security > Firewalls

Firewalls

Firewalls are routers which are usually configured to block all traffic except that on specific ports, usually the web service ports 80 and 443. This may insulate your intranet from the Internet, but at the cost of increased difficulty of maintenance because it will be impossible to telnet in from the outside and impossible to redirect the display of GUI’s.

There is almost no performance impact from a properly configured hardware firewall that simply blocks most ports, but firewalls that also encrypt all traffic can increase latency dramatically, easily taking twice as long to make a transfer. A couple of rules for reducing the impact of firewalls are to use dedicated firewall hardware doing nothing but firewall duty, and to put the most used rules at the top of your rules list so they are read first. Multiple firewall machines may be able to work in parallel. See Building Internet Firewalls, by Brent Chapman and Elizabeth Zwicky (O’Reilly Media).


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