zer (RSPAN), you can even send packets to another switch. RSPAN can be useful in data centers where a packet-capture device is perma- nently installed on one of many interconnected switches. With RSPAN, you can capture packets on switches other than the one with the sniffer attached (RSPAN configuration details are provided later in this section). Configure SPAN with the monitor command. You can have more than one SPAN ses- sion, each identified with a session number: Chapter 19: Catalyst 3750 Features 3750 (config) #monitor session 1 ? destination SPAN destination interface or VLAN filter SPAN filter source SPAN source interface, VLAN Having more than one SPAN session is useful when you have an IDS device on your network and you need to do a packet capture. The IDS device will require one SPAN session, while the packet capture will use another. For a monitor session to be active, you must configure a source port or VLAN, and a destination port. Usually, I configure the destination port first because the packet- capture device is already attached. If you have port security set, you must disable it before you can use the port as a SPAN destination: 3750(config)#monitor session 1 destination interface g1/0/20 %Secure port can not be dst span port Sessions can be numbered from 1 to 66, but you can only have two sessions configured at any given time on a 3750 switch. Here, I have two sessions configured (session 1 and session 10): monitor session 1 source vlan 20 rx monitor session 1 destination interface Gi1/0/10 monitor session 10 source vlan 10 rx monitor session 10 destination interface Gi1/0/20 If you try to configure more than two SPAN sessions on a 3750 switch, you will get the following error: 3750(config)#monit session 20 source int g1/0/10 % Platform can support a maximum of 2 source sessions In this example, I've configured two VLANs to be the sources, both of which will have their packets reflected to interface Gil/0/20: monitor session 10 source vlan 20 rx monitor session 10 source vlan 10 monitor sessio