Unicast Reverse Path Forwarding (Unicast RPF) in Strict Mode is a network security tool designed for use at the edge of a service-provider network.
Strict Mode vs Loose Mode
Strict mode verifies that the source address of an IPv4 packet both exists in the routing table and is reachable by a path through the input interface before forwarding a packet.
Loose mode verifies only that the source IPv4 address exists in the routing table.
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