* ``--unidir`` : run traffic with unidirectional flow (default to bidirectional flow)
+.. _adv-l2l-cli:
+
+L2 loopback test via CLI
+------------------------
+
+The CLI allows running a pure L2 loopback benchmark with the ``--l2-loopback`` option.
+Enabling this mode overrides any service chain type selected in the config file.
+The usual argument would be a single VLAN ID but the syntax has been extended.
+
+Examples of runs:
+
+* specify the vlan ID
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg --frame-size=64 --rate=100% --duration=10 --l2-loopback=123
+
+* specify a list of vlan IDs
+
+ Several service chains are created, the count is adjusted to the list size.
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg -fs=64 --rate=100% --duration=10 --l2-loopback=123,124,125
+
+* enable the mode without VLAN tagging
+
+ In this case the service chain count is forced to 1.
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg -fs=64 --rate=100% --duration=10 --l2-loopback=no-tag
+
+* use different VLAN tags for left & right side ports
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg -fs=64 --rate=100% --duration=10 --l2-loopback=111_211
+ nfvbench -c nfvbench.cfg -fs=64 --rate=100% --duration=10 --l2-loopback=111,112_211,212
+
+ .. note::
+ It may look bizarre to specify mismatched VLAN tags for left & right sides,
+ however no assumption is made about the loop implementation.
+ This could help testing some exotic L2 layer configuration comprising a VLAN rewriting.
+
+* enable the mode, starting from current settings (prepared in the cfg file)
+
+ In this case the service chain count is not adjusted.
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg -fs=64 --rate=100% --duration=10 --l2-loopback=true
+
+* disable the mode (possibly enabled in the cfg file)
+
+ .. code-block:: bash
+
+ nfvbench -c nfvbench.cfg --l2-loopback=false
+
+
MAC Addresses
-------------