Cisco Certified Internetwork Expert (CCIE) Practice Test

Which two statements about unicast Reverse Path Forwarding (uRPF) are true?

1. The administrator can configure the allow-default command

2. In strict mode, only one routing path can be used

3. It is always enabled by default

4. It does not work with multicast traffic

The correct answer is: The administrator can configure the allow-default command

In the context of unicast Reverse Path Forwarding (uRPF), the feature is designed to verify the reachability of the source address in incoming packets. This verification helps to ensure that packets have been received on an interface where they should be according to the routing table, thereby mitigating IP address spoofing. The statement about the allow-default command is accurate because this command can be utilized to permit default routes in uRPF configurations. This is particularly useful in environments where a default route exists, allowing devices to still make decisions about traffic even if they do not have a more specific path for certain sources. Regarding the other statements, it's important to understand their context. In strict mode, uRPF indeed requires that the packet must arrive on the interface that corresponds to the best route back to the source address; however, this doesn’t imply it can only use one routing path, given that strict mode enforces a singular verification but does not preclude the existence of multiple routes in the overall routing protocol design. Additionally, uRPF is not enabled by default and requires explicit configuration to function. Finally, the statement about uRPF's interaction with multicast traffic is correct; uRPF is specifically designed for unicast traffic and will not