To enable the ability to capture traffic sent and received on other switch ports, Cisco Catalyst switches include a feature called the switch port analyzer feature (SPAN), as well as remote SPAN (RSPAN) and VLAN access control lists (VACLs).
SPAN is the traditional method of monitoring LAN traffic on Cisco switches. SPAN uses the concept of mirroring traffic from a set of source ports to a single destination port, which has a network capture tool connected to it.