Overview… packet modifiers
By default the content of the packet header is identical for every packet transmitted for a stream. The only part that (optionally) varies is the length.
To generate variation on a packet-by-packet basis you can add one or more modifiers to the packet header. In the XenaManager you do this by clicking the “Add field modifier” button:
The portion to be modified is specified by the byte-position from the start of the packet and a bit-mask. These values can be specified manually or you can click the label at the left to bring up the list of fields corresponding to the protocol segments defined for the header:
Once you have specified which portion of the header is to be modified, you specify how to modify it: incrementing, decrementing, or random variation.
The packet editor strip underlines the bytes that are affected by a modifier:
It uses a similar dashed underline for fields that are automatically modified by the hardware, in particular the IPv4 header’s length and checksum fields:
By default the bits corresponding to the mask are run through all possible values. But for incrementing and decrementing modifiers you can specify explicit start, step, and stop values, by clicking the little arrow left of the label:
This section also allows you to specify a repeat count for the modifier. By default each packet that is generated for the stream will get a new value of the modified portion. With the repeat count you slow down the modifier so multiple packets will retain the same value before going to a new value.
When you have multiple modifiers this allows you to create a coupling between them so that together they sweep over a combined range of values. If the repeat count is left blank (corresponding to 1) the modifiers will run independently and each will change for every packet.