Cisco N7K-C7010 Configuration Guide - Page 131

Chapter 5 Configuring Bidirectional Forwarding Detection Information About BFD Send document comments to [email protected] Figure 5-2 shows what happens when a failure occurs in the network (1). The BFD neighbor session with the OSPF neighbor router is torn down (2). BFD notifies the local OSPF process that the BFD neighbor is no longer reachable (3). The local OSPF process tears down the OSPF neighbor relationship (4). If an alternative path is available, the routers immediately start converging on it. Note The BFD failure detection occurs in less than a second, which is much faster than OSPF Hello messages could detect the same failure. Figure 5-2 Tearing Down an OSPF Neighbor Relationship OSPF 3 BFD 172.18.0.1 Router A 172.16.10.2 4 OSPF neighbors X BFD neighbors X 2 1 X 172.16.10.1 OSPF 3 BFD Router B 172.17.0.1 196277 Distributed Operation Cisco NX-OS can distribute the BFD operation to compatible modules that support BFD. This process offloads the CPU load for BFD packet processing to the individual modules that connect to the BFD neighbors. All BFD session traffic occurs on the module CPU. The module informs the supervisor when a BFD failure is detected. BFD Echo Function The BFD echo function sends echo packets from the forwarding engine to the remote BFD neighbor. The BFD neighbor forwards the echo packet back along the same path in order to perform detection; the BFD neighbor does not participate in the actual forwarding of the echo packets. The echo function and the forwarding engine are responsible for the detection process. BFD can use the slow timer to slow down the asycnhronous session when the echo function is enabled and reduce the number of BFD control packets that are sent between two BFD neighbors. Also, the forwarding engine tests the forwarding path on the remote (neighbor) system without involving the remote system, so there is less interpacket delay variability and faster failure detection times. The echo function is without asymmetry when both BFD neighbors are running echo function. Note Unicast Reverse Path Forwarding check (uRPF) is disabled by default. If you need to enable it on an interface functioning with BFD, the BFD echo function must be disabled. OL-23435-03 Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x 5-3