Netopia 2200 - Manual (Page 149)

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Firewall Tutorial
and a packet goes through these rules destined for FTP, the packet would for ward through
the first rule (WWW), go through the second rule (FTP), and match this rule; the packet is
allowed through.
If you had this filter set for example....
Allow WWW access;
Allow FTP access;
Deny FTP access;
Deny all other packets.
and a packet goes through these rules destined for FTP, the packet would for ward through
the first filter rule (WWW), match the second rule (FTP), and the packet is allowed through.
Even though the next rule is to deny all FTP traffic, the FTP packet will never make it to this
rule.
Implied rules
With a given set of filter rules, there is an Implied rule that may or may not be shown to the
user. The implied rule tells the filter set what to do with a packet that does not match any
of the filter rules. An example of implied rules is as follows:
Implied Meaning
Y+Y+Y=N If all filter rules are YES, the implied rule is NO.
N+N+N=Y If all filter rules are NO, the implied rule is YES.
Y+N+Y=N If a mix of YES and NO filters, the implied rule is NO.