The loop2 test sends a NULL XID frame to the broadcast (all 1's) destination MAC address. The source SAP (Service Access Point) value used is 0x04 (SNA's SAP). Therefore, if SNA is running on the system, the loop2 test will fail. The destination SAP value is the NULL SAP (0x00). This test finds out who is listening and can receive frames sent out from a node. The verbose (-v) option displays the MAC address of responding nodes. All possible responders may not be displayed, since the loop2 test only waits for responses for 2 seconds, but during this time 50-200 nodes may be displayed. The most likely error is:

Unexpected DLPI primitive x, expected y.

where x = 5 and y = 6. From /usr/include/sys/dlpi.h, the expected return value from one of the DLPI primitives is 6 (DL_OK_ACK), but instead a 5 (DL_ERROR_ACK) was received. This can occur for two reasons:

• The loop2 command was issued to a non-existent PPA (Physical Point of Attachment).
• The SAP (0x04) is already in use (for example, the SNA subsystem is up).

The loop3 test sends 1,495 byte Unnumbered Information (UI) frames to the NULL (all 0's) destination MAC address. This should be used along with data capture either on the local node or another node on the same LAN to verify the transmission of data. The ppa argument specifies the adapter on which to run the test. The ppa is the relative physical position of the adapter and may be ascertained by viewing the adapter configuration (see llc2_config(1)). For Token Ring or Ethernet, specify an even sap value from 2 through 254, or, for Ethernet only, any type value from 1519 (0x05ef) through 65535 (0xffff). It is advised to pick a value that is easily recognized when the data capture output is viewed. frames is the decimal number of 1,495 bytes packets to transmit. The test will only display a message if a failure occurs.

The loop4 test sends a TEST frame (no information field) to the broadcast (all 1's) destination MAC address. The source SAP value used is 0x04 (SNA's SAP). Therefore, if SNA is running on the system, the loop4 test will fail. The destination SAP value is the NULL SAP (0x00). This test finds out who is listening and can receive frames sent out from a node. The verbose (-v) option displays the MAC address of responding nodes. All possible responders may not be displayed since the loop4 test only waits for responses for 2 seconds, but during this time 50-200 nodes may be displayed. The loop4 test displays information similar to the following example if other nodes are listening and respond (verbose mode):

-Attaching -Binding -Sending TEST -Responders 1-0000c0c12449 2-08000e142990 3-08000e142a51 4-0000c0450044 5-0000c0199e46 -Unbinding -Detaching 5 nodes responding

The errors displayed are the same as for loop2.