The second principle is to implement BCP38 and this is unicast reverse path forwarding which means deny outbound traffic from customers which has spoofed source addresses. We should only be allowing traffic from IP address space that's assigned to a customer's out from these customer links. Everything else is spoofed or faked, what you have and should be dropped. So the advice and the simple technique is to implement uRPF on all single home customer facing interfaces. It's much cheaper to do this in terms of CPU and RAM than implementing packet filters. We describe uRPF in more detail elsewhere in this series.

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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