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DES-7200 Configuration Guide Chapter 6 URPF Configuration
6-3
Fig 2 Asymmetrical routing
Multi-homed network is the common network application found between user and IPS or
between ISPs. As shown in Fig 3, the user network A is simultaneously connected to multiple
ISPs, and the incoming and outgoing streams are always asymmetrical. The figure shows that
user network A is visiting user network B.
Fig 3 Multi-homed network
In the above two applications, valid messages will be filtered if URPF strict mode is enabled.
Therefore, URPF loose mode is introduced.
URPF loose mode: Reverse route check is conducted according to the source IP of incoming
message. As long as the route is found, the next-hop outgoing interface may not necessarily
be the interface that receives the message. The introduction of URPF loose mode well solves
the asymmetrical stream problem in the aforementioned asymmetrical routing application and
multi-homed network.