diff --git a/README.md b/README.md
index a4b11bf..fa736c3 100644
--- a/README.md
+++ b/README.md
@@ -22,9 +22,14 @@
 
     sudo oftest/oft --test-dir=olt-oftest/ -i 1@eth1 -i 129@eth2 --port 6633 -V 1.3
 
-If you need to change the port numbers used, for example to use ONU port 3:
+Most forwarding tests use 1 ONU port, and some multicast tests use 2 ONU ports.
+By default the tests use ONU ports 1 and 2, and OLT port 129. If you need to change the port numbers used by the tests, you can set them using test-params.
 
-    sudo ./oftest/oft --test-dir=olt-oftest/ -i 1@h1-eth0 -i 129@h129-eth0 --port 6633 -V 1.3 --test-params="onu_port=3:olt_port:129"
+For example, to use the ONU ports 130 and 131, and OLT port 258, the following command can be used:
+
+    sudo ./oftest/oft --test-dir=olt-oftest/ -i 130@h1-eth0 -i 131@h2-eth0 -i 258@h129-eth0 --port 6633 -V 1.3 --test-params="onu_port=130;onu_port2=131;olt_port:258;"
+
+The port numbers must be set correctly in the -i arguments which are local interface connected to hardware ports, and in the --test-params argument.
 
 ---