Overview
Unicast Reverse Path Forwarding (URPF) protects a network against source spoofing attacks, such as DoS and DDoS attacks.
Attackers send packets with a forged source address to access a system that uses IP-based authentication, in the name of authorized users or even the administrator. Even if the attackers do not receive response packets, they are still disruptive.
Figure 124: Source address spoofing attack
As shown in Figure 124, an attacker on Router A sends the server (Router B) requests with a forged source IP address 2.2.2.1. Router B sends response packets to IP address 2.2.2.1 (Router C). Consequently, both Router B and Router C are attacked. URPF can prevent such attacks.
The term "router" in this document refers to both routers and Layer 3 switches.