1. Ingress filtering verifies the source addresses of incoming traffic to prevent spoofing, while egress filtering verifies outgoing traffic to prevent internal threats from spreading.
2. Separate filtering helps isolate parts of the network and only allow expected communication patterns between servers, workstations, and the internet.
3. We need to separately filter ingress and egress traffic to harden network security by blocking unauthorized internal and external access and communication, and containing any threats that do arise.