In sequential mode, the service scanning cannot be started until port scanning results are available for all the ports and the hosts are scanned. Thus, a pen tester may have to wait to obtain these results. Also, in this mode, the pen tester does not have control over which services can be scanned first and which can be scanned later. All the services are scanned in one go, limiting the granularity of control over service scanning. These are the limitations of the sequential mode that is handled by the concurrent mode.

The concurrent mode offers the flexibility to launch service scanning the moment service discovery is finished and further gives an option to launch service scanning for selective services based upon the pen testers choice.

1.  Click on New Scan tab under the Scan tab.
2.  Fill in the scan parameters and choose the scan mode as Concurrent:

3. The remaining steps will be the same, with the only exception being that in this mode of scan, a user will not have to wait for all hosts and ports to be scanned to begin with service scanning. Also, the user can choose what services he may wish to scan. This is illustrated in the following figure:

As you can see in the preceding screenshot, a user can choose to scan http first and not scan ssh immediately. The user can decide when to scan what service.

 All the capabilities (reconfiguration, viewing results and so on) are available with the concurrent mode as well.