https://docs.128technology.com/docs/config_reference_guide
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.