Address Masks

Spirent TestCenter can automatically generate a large number of addresses quickly based on a few configuration parameters. These include:

• Start, the first address in the list
• Step, the amount added to each address to make the next address
• Mask, a value that tells Spirent TestCenter where in the address to add the step value
• Count or End, a count value indicates the number of addresses to create; an end value indicates the last address to create

Masks

A mask is a binary value that uses a one to indicate that values in that position can be incremented and a zero indicate that values in that position must be ignored. Masks are often expressed in decimal or hexadecimal, but regardless of how they are expressed, they work at the binary level.

The first two examples are contiguous bitwise masks because the ones are all contiguous. At no point in the mask is a zero interposed between ones.

The last two examples are noncontiguous bitwise masks. One or more zeroes appear between sets of ones.

Example: IPv4 Address

On the first increment, the value of 128 is added to the 1 in the second octet, resulting in the value of 129. On the second increment, the sum produces a 1 in the second octet and carries over to the third octet, incrementing the 85 to an 86. The result is five addresses with a 1 in the second octet, and five with a 129 in the second octet.

Example: MAC Address

In this example, Spirent TestCenter generates 512 addresses in the 00:10:94:00:xx:xx range and 488 in the 00:10:94:01:xx:xx range.

Example: MAC Address with a noncontiguous bit mask

This example uses a noncontiguous bitwise mask. Four addresses are generated.