Overview… filters and terms
Every port has a filter mechanism for inspecting all the received packets and recognizing particular patterns within the packets. Filters are defined under their own “Filters” tab in the content area of the XenaManager.
Filters are independent of the test payloads and provide an alternative method for analyzing the train of received packets.
Filters are logical expressions on a number of basic true-or-false terms, which can be of two types: match terms and length terms.
Match terms look for a particular pattern of bits at a particular position within each packet:
Like for modifiers, a match term will typically correspond to a particular protocol field.
And like for modifiers, in the XenaManager you can click the field label to specify the position and mask as a protocol field. However, since a filter is not related to any stream definition you need to manually click the “Add” button to build the needed protocol segments:
Length terms look for packets that are longer or shorter than a particular size:
Match terms are named M0, M1, M2, … and length terms are named L0, L1, L2, … These names are used when the terms are combined using a Boolean expression to form a filter condition:
The condition can use the usual Boolean operators &, |, and ~. As usual, the | operator has lowest precedence.
Any term can be used in any number of filter conditions for the port, so for instance a match term looking for a particular VLAN tag can be used in multiple conditions for packets using that tag.
Filters can be used in different ways: the port will accumulate separate statistics for packets satisfying the filter condition, the capture mechanism can use the filters as start/stop/keep criteria, and likewise for the histogram mechanism.