+| | ${args}= | Run Keyword If | '${encaps_tx}' == '${EMPTY}'
+| | | ... | Set Variable | ${args}
+| | ... | ELSE | Catenate
+| | ... | ${args} | --encaps_tx ${encaps_tx} | --vlan_tx ${vlan_tx}
+| | ${args}= | Run Keyword If | '${encaps_rx}' == '${EMPTY}'
+| | | ... | Set Variable | ${args}
+| | ... | ELSE | Catenate
+| | ... | ${args} | --encaps_rx ${encaps_rx} | --vlan_rx ${vlan_rx}
+| | ${args}= | Run Keyword If | '${vlan_outer_tx}' == '${EMPTY}'
+| | | ... | Set Variable | ${args}
+| | ... | ELSE | Catenate | ${args} | --vlan_outer_tx ${vlan_outer_tx}
+| | ${args}= | Run Keyword If | '${vlan_outer_rx}' == '${EMPTY}'
+| | | ... | Set Variable | ${args}
+| | ... | ELSE | Catenate | ${args} | --vlan_outer_rx ${vlan_outer_rx}