Limitations of packet capture

You must be aware of certain limitations of packet capture.


In the Library Manager, Application page, the Default Network Device field must be set to a physical interface.

Packet capture basics

Packet capture refers to the interception of a data packet as it travels across a network. Packet capture (as opposed to using an External Proxy Server) is an option when setting the Recording mode for the following transports:
  • TCP
  • FIX
  • HTTP
Packet capture requires specialized software:
  • On Windows systems, Network Packet Capture is included in the HCL OneTest™ API installation program. If necessary, you can rerun IBM® Installation Manager to add Network Packet Capture to the installation. See Installing HCL OneTest API.
  • On non-Windows systems, libpcap is typically installed by default. If necessary, you can download the latest package from

If you choose Packet Capture as your Recording mode, HCL OneTest API calls the appropriate packet capture software automatically.


Although packet capture is simpler than using an external proxy server, be aware of the following limitations:
  • Your system administrator might not allow the use of packet capture software due to security concerns with intercepting traffic.
  • On non-Windows systems, root permissions are required to access the network port in promiscuous mode, and thus to run packet capture.
  • Packet capture does not work with wireless network adapters. Make sure that the Default Network Device in Library Manager is set to a physical interface.
  • You can record only those messages that are sent from, or received by, the system running HCL OneTest API. You cannot record messages between remote systems.
  • Packet capture cannot access messages that are sent locally on a Windows system, because these messages go through the internal loopback connector. For more information about the internal loopback connector, see