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Cisco ASA and PIX Firewall Handbook by Dave Hucaby

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3-1. Configuring Interfaces

Every firewall has one or more interfaces that can be used to connect to a network. To pass and inspect traffic, each firewall interface must be configured with the following attributes:

  • Name

  • IP address and subnet mask (IPv4; beginning with PIX 7.x, IPv6 is also supported)

  • Security level (a higher level is considered more secure)

Traffic is allowed to flow from a higher-security interface to a lower-security interface (“inside” to “outside,” for example) as soon as access list, stateful inspection, and address translation require-ments are met. Traffic from a lower-security interface to a higher one must pass additional inspection and filtering checks.

Firewall interfaces can be physical, where actual network media cables ...

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