Which two statements about troubleshooting with Unicast reverse Path Forwarding are true? (Choose two.)
A. uRPF allows packets with source 0.0.0.0 and destination 255.255.255.255 to pass.
B. uRPF drops packets with source 0.0.0.0 and destination 255.255.255.255.
C. Cisco Express Forwarding must be enabled for uRPF to work.
D. Cisco Express Forwarding must be disabled for uRPF to work.
E. uRPF configuration is supported on Layer 2 and Layer 3 Cisco devices.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_data_urpf/configuration/15-sy/sec-data-urpf-15-sy-book/cfg-unicast-rfp.html
“Unicast RPF with BOOTP and DHCP
Unicast RPF will allow packets with 0.0.0.0 source and 255.255.255.255 destination to pass so that Bootstrap Protocol (BOOTP) and Dynamic Host Configuration Protocol (DHCP) functions work properly. This enhancement was added in Cisco IOS Release 12.0 and later, but it is not in Cisco IOS Release 11.1CC. ”
“When Unicast RPF is enabled on an interface, the router examines all packets received as input on that interface to make sure that the source address and source interface appear in the routing table and match the interface on which the packet was received. This “look backwards” ability is available only when Cisco express forwarding (CEF) is enabled on the router, because the lookup relies on the presence of the Forwarding Information Base (FIB). CEF generates the FIB as part of its operation. “