Question : Problems Using Port Spanning on Cisco 3550

Hi All,

I have purchased a copy of Network Instruments Observer suite, but am having problems with my port spanning on my Catalyst 3550.

Here's my set up.

In the server room, we have a 24 Port Catalyst 3550 which is our core switch, all the servers and other switches are linked through this one.

I have a cable patched into Port 1 on the switch to my machine down here, which has a Network Instruments PCMCIA card in (promiscuous)

If want to port span one of the ports to monitor it and send the traffic through to this port I am entering the following (Port 16 is the example in this)

CATALYST_9#conf t
CATALYST_9(config)#monitor session 1 source interface Fa0/16
CATALYST_9(config)#monitor session 1 destination interface Fa0/1
CATALYST_9(config)#exit
CATALYST_9#show monitor session 1

Session 1
---------
Type              : Local Session
Source Ports      :
    Both          : Fa0/16
Destination Ports : Fa0/1
    Encapsulation : Native
          Ingress: Disabled

So all looks OK, but as soon as I make these changes, it effectively disables the PCMCIA card connection that is plugged into Port 1

How do I stop this? I can't even ping anything, to get my connection back I have to hyperterminal in from another machine and remove the monitor ports.

Many Thanks
Andy

Answer : Problems Using Port Spanning on Cisco 3550

ingress traffic on a destination port is not supported on the 3550:

"When you configure a switch port as a SPAN destination port, it is no longer a normal switch port; only monitored traffic passes through the SPAN destination port. "
Reference
http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration_guide_chapter09186a00801f0a55.html

It just does not make sense to me that if you have network access with NIC#1 plugged into switch port 0/X and you enable NIC#2 in promiscuous mode that is plugged into port 0/1, that NIC#1 will stop functioning..