Configure CISCO Catalyst 2960 ports to monitoring/mirroring mode

This will send all traffic that comes on the 0/1-0/9 ports to the Ga0/1 interface:

switch>enable
switch#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.

switch(config)#monitor session 1 source interface fastEthernet 0/1
switch(config)#monitor session 1 source interface fastEthernet 0/2
switch(config)#monitor session 1 source interface fastEthernet 0/3
switch(config)#monitor session 1 source interface fastEthernet 0/4
switch(config)#monitor session 1 source interface fastEthernet 0/5
switch(config)#monitor session 1 source interface fastEthernet 0/6
switch(config)#monitor session 1 source interface fastEthernet 0/7
switch(config)#monitor session 1 source interface fastEthernet 0/8

switch(config)#monitor session 1 destination interface gigabitEthernet 0/1

Show info:

switch#show monitor session 1
Session 1
---------
Type    : Local Session
Source Ports :
 Both: Fa0/1-8
Destination Ports : Gi0/1
 Encapsulation : Native
  Ingress : Disabled

And now we can capture this traffic:

# tcpdump -i eth0 -n