AN 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. Note that if you have port security set, you must disable it before you can use the port as a SPAN destination: (config)# monitor session 1 destination interface g1/0/20 %Secure port can not be dst span port Sessions can be numbered from 1-66, but you can only have two sessions config- ured 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)# monitor 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 session 10 destination interface Gi1/0/20 You can also monitor one or more interfaces. Multiple interfaces can be configured separately, or on a single configuration line: 3750(config)# monitor session 11 source interface g1/0/11 3750 (config)# monitor session 11 source interface g1/0/12 Entering the two preceding commands results in the following line being added to the configuration: monitor session 11 source interface Gi1/0/11 - 12 The sources in a monitor session can be configured as either receive (rx), transmit (tx), or both. The default is both: 3750 (config)# monitor session 1 source int g1/0/12 ? Specify another range of interfaces Specify a range of interfaces Monitor received and transmitted traffic Monitor received traffic only Monitor transmitted traffic only Interfaces should 