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Network packets can be filtered with a program that is passed to the underlying packet capture code. The filter program is specified on the sniffer configuration page, in the program area. Simple filter programs can be specified by selecting various options as described below. More complicated filters are the same as those passed on the command line to the tcpdump(8) command, and have to be entered directly. Note the the filter program is applied to each packet on the network.
The Use program checkbox controls whch if the above two cases applies; to enter full tcpdump(8) filter programs, it should be checked. Note that controls in the program area are enabled and disabled as appropriate, however, the program generated in simple mode is shown in the bottom-most field (and can then be edited if Use program is checked.
As noted above, when the Set button is pressed, the filter program equivalent to the above settings appears in the bottom-most control. If the Use program box is then checked, it can be edited further; pressing Set again will then use this filter program.
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