You enable unicast reverse path forwarding on the ge-0/0/1.0 interface A packet is received on the ge-0/0/1.0 interface with a source address of 10.10.10.10. A route lookup determines that the next hop for the 10.10.10.10 address is the ge-0/0/1.0 interface. In this scenario which action is performed?
When Unicast Reverse Path Forwarding (uRPF) is enabled on an interface, it checks the source address of incoming packets against the router's forwarding table to ensure that the source address is reachable via the same interface. In this scenario, since the route lookup determines that the next hop for the source address 10.10.10.10 is the same interface (ge-0/0/1.0) on which the packet was received, it means that the source address is considered valid. Consequently, the packet passes the uRPF check and is forwarded.
B: The packet it forwarded - https://www.juniper.net/documentation/us/en/software/junos/security-services/topics/topic-map/interfaces-configuring-unicast-rpf.html
B. Packet is forwarded not discarded.
interface is same for lookup as where the packet is received.
D is your answer. This is because Unicast Reverse Path Forwarding (RPF) is used to prevent the spread of network misconfigurations and malicious traffic, such as spoofed IP addresses. When RPF is enabled on an interface, it checks the source address of incoming packets against the routing table to verify if the incoming interface is the expected path for that source address. If the incoming interface is not the expected path, the packet is discarded. In this scenario, the route lookup determines that the next hop for the source address 10.10.10.10 is the same interface the packet was received on, which is the ge-0/0/1.0 interface. This means the source address is not reachable through another interface, therefore the packet is considered to be a spoofed packet and is discarded
That's the thing. An IP is expected to be received on an interface where it is also used as the primary route to the same IP. Imagine this scenario with a simple diagram of PC1 > R1 > R2 > R3. If PC1 spoofed its IP to the same IP as R2, then R3 receives the packet from R1>R2, it would then reply back to R2 itself (as this is the source IP that was spoofed by PC1). R2 would then reply back as it would think that it's an initiated ICMP from R3. Now imagine this with 1000000 ICMP being sent from PC1. DOS attack would occur on R2 and R3. Hence, URPF can be used and configured on R1's interface facing PC1 so that it would check if the source of PC1 is reachable to the interface on where its connected to prevent this.
Key phrase to take note off : A ROUTE LOOKUP determines that THE NEXT HOP for the 10.10.10.10 address "IS" the ge-0/0/1.0 interface. So the packet in question, which was received on the ge-0/0/1.0 interface had a "fake" source IP address, meaning it's likely a spoofing attack. Hence the packet is not only rejected but discarded (silently dropped, with no ICMP sent back)
return traffic would go through the same interface and that is allowed for rpf. So this packet is forwarded.
Answer B
B is the correct answer.
B: The packet it forwarded - https://www.juniper.net/documentation/us/en/software/junos/security-services/topics/topic-map/interfaces-configuring-unicast-rpf.html
B is the correct answer If a device running Junos OS receives a packet with a source address of 10.10.10.10 on interface ge-0/0/1.0 and the you configured the device to perform the unicast RPF check on that interface, it examines its routing table for the best route to 10.10.10.10. If the route lookup returns a route for 10.10.10.0/24 with a next hop of interface ge-0/0/1.0, the packet passes the unicast RPF check and is accepted.
the provided answer is Correct uRPF checks the source address, and interface
B: The packet it forwarded - https://www.juniper.net/documentation/us/en/software/junos/security-services/topics/topic-map/interfaces-configuring-unicast-rpf.html
Packet is Forwarded
Ref: Understanding How Unicast Reverse Path Forwarding Prevents Spoofed IP Packet Forwarding - TechLibrary - Juniper Networks "Understanding How Unicast Reverse Path Forwarding Prevents Spoofed IP Packet Forwarding ... A unicast reverse-path-forwarding (RPF) check is a tool to reduce forwarding of IP packets that might be spoofing an address. A unicast RPF check performs a forwarding table lookup on an IP packet’s source address, and checks the incoming interface. The router or switch determines whether the packet is arriving from a path that the sender would use to reach the destination. If the packet is from a valid path, the router or switch forwards the packet to the destination address. If it is not from a valid path, the router or switch discards the packet. ..."
b is the correct answer
It’s B
B. same src addess and src interface checked, packet is forwarded