RB1100 firewall setup on switch1

I have configured a RB1100 with two subnets …54.16/240 & 55.0/0, Port 1 has an IP address of ..54.18 and the ISP’s router has an IP address of ..54.17, ports 2, 3, 4, 5, have a Master of port1.
The problem I have is to try and monitor traffic going to a device with IP addr of ..54.20 connected to port 3 on switch 1. It would seem that any traffic comming in on port 1 and staying within switch 1 is not monitored by the firewall function. Is this correct, and is there any way I can monitor the traffic on switch 1.
Note: Any traffic arriving on port 1, switch 1 and destined for the other subnet (…55.0/0 ) defined on switch 2 works just fine.
Any suggestions or pointers to examples would be helpful.
Thanks Poul