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Routing & Switching · Advanced

Unicast Reverse Path Forwarding (uRPF)

A feature that drops packets whose source address is not reachable via the routing table, mitigating spoofing.

Definition

Strict mode requires the source to be reachable via the same interface the packet arrived on, which suits single-homed edges. Loose mode only requires a route to the source to exist via any interface, suiting asymmetric multihomed networks. A default route satisfies loose mode unless allow-default is excluded.

Example

ip verify unicast source reachable-via rx

Exam tip

Use loose mode where routing is asymmetric; strict mode would drop legitimate traffic.

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