[c-nsp] Question about SPAN session

[Hugo Rebello]

Guys,

I have a doubt about SPAN session using "monitor session" command in 
Cisco switches.
I want to monitor my E-mail Server via sniffer (Ntop in Linux), and I 
have a Cisco Catalyst 2950 switch.
So, When I insert the commands below in the switch, my sniffer server 
stop the communication with the others machines.

monitor session 1 source interface fa 0/16 (E-mail Server is connected here)
monitor session 1 destination interface fa 0/38 (Sniffer Server is 
connected here)

Why is it happened ?
I don't know what is wrong.

Thank you.

Cheers,
Hugo