Hello,
the 3550 supports a feature called port security, which allows you to define which MAC addresses are allowed on a switchport. Here are a few configuration examples, in case you cannot access the link below:
This example shows how to enable port security on a port and to set the maximum number of secure addresses to 50. The violation mode is the default, no static secure MAC addresses are configured, and sticky learning is enabled.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface fastethernet0/1
Switch(config-if)# switchport mode access
Switch(config-if)# switchport port-security
Switch(config-if)# switchport port-security maximum 50
Switch(config-if)# switchport port-security mac-address sticky
Switch(config-if)# end
This example shows how to configure a static secure MAC address on a port and enable sticky learning:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface fastethernet0/2
Switch(config-if)# switchport mode access
Switch(config-if)# switchport port-security
Switch(config-if)# switchport port-security mac-address 0000.02000.0004
Switch(config-if)# switchport port-security mac-address sticky
Switch(config-if)# end
This example shows how to configure a maximum of eight secure MAC addresses on VLAN 5 on a port:
Switch(config-if)# switchport port-security maximum 8 vlan 5
Switch(config-if)# end
Configuring Port-Based Traffic Control
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12120ea2/3550scg/swtrafc.htm
HTH,
GP
