From what I have read, you can use the switchport monitor command on ASA 5505's to setup a Span port due to the back of the ASA actually being a switch.
On my 5520, I do not see the switchport command listed when issuing a ? via the CLI. How do people monitor traffic on non-5505's? My goal is to connect our IDS/IPS device that is running is promiscuous mode to a Ethernet port on the 5520 to monitor WAN traffic.
I do not want to have to pass the WAN traffic through a switch as it would require me to get two (for redundancy) STP/switchport capable switches. Also, we have the 4GE SSM module for fiber WAN connectivity installed on the device so adding the IPS module is not an option.
Our IPS system is the Cisco IPS 4240. Would another option be to have Netflow or verbose syslog messages sent to the IPS device?
Guide to setting up switchport access on a 5505: http://www.wr-mem.com/?p=66