A.Create an additional ACL to block the access to VLAN 1.
B.Move the management VLAN to something other than default.
C.Move all ports to another VLAN and deactivate the default VLAN.
D.Limit the access in the switch using port security configuration.
E.Use static VLAN in trunks and access ports to restrict connections.
F.Shutdown all unused ports in the Catalyst switch.

A.source ip address:192.168.15.5;destination port: 21
B.source ip address:,192.168.15.37 destination port: 21
C.source ip address:,192.168.15.41 destination port: 21
D.source ip address:,192.168.15.36 destination port: 23
E.source ip address:192.168.15.46;destination port: 23
F.source ip address:,192.168.15.49 destination port: 23