Application Scenarios for URPF

URPF Strict Check

AS1 and AS2, respectively, establish a single connection with AS3.

As shown in Figure 1, AS1 and AS2 establish a single connection with AS3, respectively. URPF is enabled on Interface1 and Interface2 of SwitchC to protect AS3 from source address spoofing attacks from AS1 and AS2.

Assumes that PC A in AS1 generates a packet with the bogus source IP address 10.2.2.2 and sends the packet to the server in AS3. After receiving the packet, SwitchC checks the inbound interface of the packet and finds that the packet with the destination IP address 10.2.2.2 must reach SwitchC through Interface2. SwitchC considers the packet as a bogus packet and discards it.

The packet sent from AS2 to the server is forwarded after passing URPF check.

Figure 1 URPF strict check application

URPF Loose Check

URPF is used when multiple connections are set up between two network edge devices.

• Single-ISP scenario

  Figure 2 URPF enabled in the single-ISP scenario
  
  

  As shown in Figure 2, two connections are set up between the enterprise and ISP devices to ensure reliability. In this case, route symmetry between the enterprise and ISP devices cannot be ensured. Therefore, URPF loose check is used.

• Multi-ISP scenario

  Figure 3 URPF enabled in the multi-ISP scenario
  
  

  As shown in Figure 3, the enterprise is connected to several ISPs. Route symmetry between the enterprise and the two ISP devices cannot be ensured. Therefore, URPF loose check is used.

  URPF enabled on multi-homed client connected to several ISPs can be applied to the following situations:

  • If specified packets are required to pass the URPF check in any situations, you can create an ACL to permit packets with specified source IP addresses to pass through.

  • The devices connected to users may only have a default route to the ISP. Therefore, matching the default routing entry needs to be supported.