Rule Syntax

The basic syntax for a rule is:

Service Source_address Destination_address optional_Time optional_Encryption "action" optional_Proxy

where:

• Service - An individual network service or a group of services provided to users. Sample services are smtp, rlogin, and ftp.

• Source_Address - An address object from the client side over which these services are provided to users. Named addresses to define the network elements that make up the configuration. A named address can represent an individual address, a range of addresses, or a group of addresses. Named addresses are also used to define the network interfaces.

• Destination_Address - An address object from the server side over which these services are provided to users. Named addresses to define the network elements that make up the configuration. A named address can represent an individual address, a range of addresses, or a group of addresses. Named addresses are also used to define the network interfaces.

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  Note -

  The version of SKIP that you can use for encryption, is one of two forms: (1) SKIP_VERSION_1 source_cert dest_cert key_algorithm data_algorithm, or (2) SKIP_VERSION_2 source_cert dest_cert key_algorithm traffic_algorithm mac_algorithm.

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Encryption is only supported if ALLOW is selected. It is not supported if any proxy or VPN is selected. Encryption works as follows:

• If the first certificate is local (the secret key is loaded into SKIP on the Screen), then the rule is considered an encryption rule. The packet will be encrypted on its way out of the Screen.

• If the second certificate is local, then the rule is considered a decryption rule, and the packet will be verified as having been decrypted accordingly (correct certificates and algorithms) before it is allowed to pass.

• If neither certificate or if both certificates are local, then the rule is ignored by the compilation process.

• Action - What the Screen should do with packets. The choices are ALLOW and DENY. The syntax for specifying an action is in the form: ALLOW LOG_options SNMP_options; for example, ALLOW LOG_SUMMARY SNMP_NONE,or DENY LOG_options SNMP_options ICMP_options; for example DENY LOG_SUMMARY SNMP_NONE ICMP_HOST_UNREACHABLE.

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  Note -

  Using the underscore with LOG, SNMP, and ICMP options is optional; for example, LOG_SUMMARY or LOG SUMMARY.

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• Proxy - (Optional) The name of the proxy to be enabled and any flags for the proxy. Proxy flags are only permitted in a rule when the service is a PROXY_* service, where * is the type of proxy and the flags must be of the type for that proxy. The syntax for specifying a proxy is in the form: PROXY_proxy_name proxy_name flags; for example, PROXY_HTTP HTTP flags, PROXY_FTP FTP flags, or PROXY_SMTP SMTP flags. The telnet proxy does not take flags.

• User - (Optional) A name in the proxy database of users. The syntax for specifying a user is USER user_name, where user_name is a name in the proxy database.

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  Note -

  The optional User field is only supported if the rule is Proxy-ftp or Proxy-telnet. Otherwise, the Screen does not support user-based rule criteria.

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• Time - (Optional) A component by means of which you can set up time-of-day-based Policy Rules. The syntax for specifying time is in the form: time_object_name.

• VPN - (Optional) A component by means of which you to no longer specify all the SKIP information, but have the Screen do it. The syntax for specifying VPN is in the form: vpn_name.

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  Note -

  VPN is not support if any SKIP information is specified, if DENY is selected, or if any Proxy is specified.

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