What’s uRPF checking first when the packet enters the interface ? or when unicast reverse patch forwarding is configured on interinterface.
A. it check the ingress access list
B. it check the egress access list
C. Route available in FIB ot it verifies a reverse patch via the fib to the source
D. it verify that the source has a
Difficult. The question is about what is uRPF checking first.
i would say uRPF does not check the ingress access list due to the fact that the ingress access list will work even when uRPF feature is NOT enabled.
Yes, the ingress access list is checked first – but this is not done by uRPF.
from the CCNP Official Cert Guide:
-) uRPF check the source IP of a packet arriving on an interface and determine wheter that IP is reachable, based on the router’s FIB
-) an ACL is checked only when a uRPF check fails.
The Question doesnt say there is an ACL applied to the interface.
So, for me answer C is correct
Answer A:
https://www.cisco.com/c/en/us/td/docs/ios/12_2/security/configuration/guide/fsecur_c/scfrpf.html#wp1000928
Good aswer is A
Bad response C
When a packet is received at the interface where Unicast RPF and ACLs have been configured, the following actions occur:
Step 1 Input ACLs configured on the inbound interface are checked.
Step 2 Unicast RPF checks to see if the packet has arrived on the best return path to the source, which it does by doing a reverse lookup in the FIB table.
Step 3 CEF table (FIB) lookup is carried out for packet forwarding.
Step 4 Output ACLs are checked on the outbound interface.
Step 5 The packet is forwarded.