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How Configuration is applied?

Snort assigns every incoming packet to a unique configuration based on the following criteria. If VLANID is present, then the innermost VLANID is used to find bound configuration. If the bound configuration is the default configuration, then destination IP address is searched to the most specific subnet that is bound to a non-default configuration. The packet is assigned non-default configuration if found otherwise the check is repeated using source IP address. In the end, default configuration is used if no other matching configuration is found.

For addressed based configuration binding, this can lead to conflicts between configurations if source address is bound to one configuration and destination address is bound to another. In this case, snort will use the first configuration in the order of definition, that can be applied to the packet.

Eugene Misnik 2013-05-08