Installing and Administering PPP

Chapter 5 91
Security Techniques
Filters
Filters
A ruleset is made up of one to four filters that regulate the response to a
packet. The filter’s actions are defined by its initial keyword. Each type
of filter may be used one time per connection. The following table
explains the keywords, the types of packets affected by the filters, and
the filter’s actions:
Filters defined in a ruleset replace any previous default definition for
that filter. Defined filters are not additive with a default filter. If one of
the keyword filters does not appear in a ruleset, that filter is defined by
its the most recently parsed default ruleset. If there is no previous
default ruleset, the implicit default is ‘all’, except for the log filter, which
defaults to ‘!all’.
Keyword Packet Type Action
bringup outgoing dialup Defines packets that cause a connection to be
established.
keepup inbound and outbound
dialup
Defines packets that cause the idle timer to
be reset, preventing the connection from
going down.
pass all packets Defines packets that are allowed to pass
through the filter. Packets that do not pass
cannot cause a connection to be established.
log all packets Defines the characteristics that will cause a
message about a packet to be added to a log
file.