(In the book, the importance of layer-2 security is emphasized through layer-2 attack scenarios and countermeasures for these attacks; and the future and popular layer-2 security system structures and technologies, including wire speed ACL, IEEE802.1AE, CiscoINBS, and security pseudowire combining IPSec and L2TPv3. Understand that network security is not just about firewalls, intrusion detection systems, or even content filtering devices. Without these devices, the use of switches at the second layer of the network can also enforce network security.
LAN Switch Security Cisco.Press.LAN.Switch.Security.Sep.2007.pdf)