====== Driver test: high-MTU loopback ======

===== Rationale =====

To support operation as a VLAN trunk device, drivers should be able to support a frame size of 1518 bytes (excluding the Ethernet CRC), which corresponds to an MTU of 1504 bytes.  The ''[[:cmd:lotest]]'' command allows an arbitrary MTU to be specified, and so can easily be used to test operation with an MTU of 1504.

===== Background =====

Refer to the basic [[:dev:drvtest:loopback|loopback test]] for background information.

{{ :clipart:nic.jpeg?237x222|A network card}}

===== Test sequence =====

  - Before starting, ensure that your network interface is directly connected to a second network interface on the same machine.
  - Boot into a version of iPXE with [[:buildcfg:LOTEST_CMD]] enabled and with support for both network interfaces.
  - Use ''[[:cmd:ifstat]]'' to identify the name of your network interface (hereafter assumed to be ''net0'') and the name of the second network interface (hereafter assumed to be ''net1'').
  - Initiate testing of the transmit datapath with an increased MTU using ''%%lotest --mtu 1504 net0 net1%%''.
  - Verify that the packet counter displayed by ''lotest'' increases steadily and rapidly.
  - Abort the test using ''Ctrl-C''.
  - Initiate testing of the receive datapath with an increased MTU using ''%%lotest --mtu 1504 net1 net0%%''.
  - Verify that the packet counter displayed by ''lotest'' increases steadily and rapidly.
  - Abort the test using ''Ctrl-C''.