Refer to the exhibit. R1 is configured with uRPF, and ping to R1 is failing from a source present in the R1 routing table via the GigabitEthernet 0/0 interface. Which action resolves the issue?
A.
Enable Cisco Express Forwarding to ensure that uRPF is functioning correctly.
B.
Modify the uRPF mode from strict to loose.
C.
Add a floating static route to the source on R1 to the GigabitEthernet0/1 interface.
D.
Remove the access list from the interface GigabitEthernet 0/0.
with uRPF strict mode, this can cause legitimate packets to be dropped, so that's something to keep in mind. In uRPF loose mode, the source of the IP packet must simply appear in the routing table. So loose mode looks for any interface in the routing table other than the default route.
https://www.cisco.com/c/en/us/td/docs/routers/ncs4200/configuration/guide/security/sec-data-urpf-ncs4200-book/sec-unicast-rpf-loose-mode.html "Prerequisites section" . I would say A makes more sense. I agree with ellen_AA as it seem to meet strict standards.
Apologies, guess B makes more sense as the question gets traffic via Gi0/1 but with strict mode only traffic from gi0/0 would be allowed (as this is upstream source). Anyway, classic asymmetric routing example that breaks uRPF.
Please note that in real life you should fix any asymmetric routing, never do quick fixes as the answer B implies.
so i agree B == CORRECT
I think it's A, if it's set to strict mode we would have seen drops at the interface. Because uRPF strict mode verifies reachability of the source + its existing in the routing table.
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