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In this case, spoofing allowed attackers to direct the large number of responses to a victim network.
What if you don't have a border router under your exclusive control?The key lies in each component complementing the others to form a complete security picture.When we think of network security, we most often think of the perimeter.Every network should have ingress and egress filtering at the border router to permit only traffic that is destined for the internal network to enter and traffic that is destined for the external network to exit.
We will cover filteringincluding ingress and egress filtersin Chapter 2, "Packet Filtering." Static packet filters, such as routers, are faster at screening traffic than stateful or proxy firewalls.
It contributes to defense in depth by filtering traffic before it enters or exits your network.