June 2010
Intermediate to advanced
224 pages
5h 18m
English
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Logical Operators in Filter Definitions
When you put multiple match conditions in a filter definition, flow-nfilter places a logical "and" between them. For example, the following filter shows all traffic that runs over TCP and has a source port of 25. This passes an email server's responses to a connection.
filter-definition TCPport25
match ip-protocol TCP
match ip-source-port port25You can use other logical operators to build very complicated filters.
Logical "or"
When I try to analyze a connection problem, I usually want to see both sides of the conversation. I want a filter that will show connections to port 25 as well as from port 25. For this, use the or operator as follows:
filter-definition email match ip-protocol TCP match ip-source-port ...
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