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Valid values: none, strict. Default: none. This configuration element determines whether or not the SSR requires that the egress interface for a reverse flow is the same as the ingress interface for a forward flow.
In practice, when set to "strict", a router will perform a uRPF (Unicast Reverse Path Forwarding) check on the reverse flow to see if the interfaces match. If they do not match, the session will not be established.