Description
This article is from the Firewalls
FAQ, by Matt Curtin cmcurtin@interhack.net and Marcus J. Ranum
mjr@nfr.com with numerous contributions by others.
32 What is a `single point of failure', and how do I avoid having one?
An architecture whose security hinges upon one mechanism has a single
point of failure. Software that runs bastion hosts has bugs. Applications
have bugs. Software that controls routers has bugs. It makes sense to use
all of these components to build a securely designed network, and to use
them in redundant ways.
If your firewall architecture is a screened subnet, you have two packet
filtering routers and a bastion host. (See question 3.2 from this section.)
Your Internet access router will not permit traffic from the Internet to get
all the way into your private network. However, if you don't enforce that
rule with any other mechanisms on the bastion host and/or choke router, only
one component of your architecture needs to fail or be compromised in order
to get inside. On the other hand, if you have a redundant rule on the
bastion host, and again on the choke router, an attacker will need to defeat
three mechanisms.
Further, if the bastion host or the choke router needs to invoke its rule to
block outside access to the internal network, you might want to have it
trigger an alarm of some sort, since you know that someone has gotten
through your access router.
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security, Internet, firewalls, ssl, port, protection, application layer, proxy server, packet screening, filtering rules, viruses, terms
