The ASA/PIX Security Appliance has default protection built in for denial-of-service (DoS) attacks. However, it also provides an interface to change the parameters, if required.
DoS attacks come in different flavors:
An attack that attempts to take up so much bandwidth on your network that the network becomes unusable
An attack that takes up so much of a system resource or CPU on a network device that it renders the device or the network unusable
A single-packet attack design so that a network device doesn't know what to do with the packet and the device stops forwarding traffic or crashes
Unfortunately, DoS attacks are easy to launch and not so easy to protect against. The ASA/PIX Security Appliance, however, ...