Hello, thank you for your help. The next day after the failure, I restart ospf_business on faulty r2. Discovery can be seen from r0 sent over the default route on r2 routing table. I was very surprised, and why? Next, how do I troubleshoot? r0 is a Layer 3 switch. The following is the recovery seen in r0-2 status. r1: bird> show ospf state all ospf_business 1016 - area 0.0.0.20 router x.y.z.1 distance 10 network x.y.z.0/28 metric 1 external 0.0.0.0 / 0 metric2 1 tag 00000001 router x.y.z.3 distance 0 network x.y.z.0/28 metric 10 external a.b.c.d/25 metric2 20 via x.y.z.1 network x.y.z.0/28 dr x.y.z.3 distance 10 router x.y.z.3 router x.y.z.1 r2: bird> show ospf state all ospf_business 1016 - area 0.0.0.30 router x.y.z.17 distance 10 network x.y.z.16/28 metric 1 external 0.0.0.0 / 0 metric2 1 tag 00000001 router x.y.z.19 distance 0 network x.y.z.16/28 metric 10 network x.y.z.16/28 dr x.y.z.17 distance 10 router x.y.z.17 router x.y.z.19 r0: <r0-switch> display ospf brief OSPF Process 100 with Router ID x.y.z.1 OSPF Protocol Information RouterID: x.y.z.1 Border Router: AS Multi-VPN-Instance is not enabled Graceful-restart capability: disabled Helper support capability: not configured Spf-schedule-interval: max 10000ms, start 500ms, hold 1000ms Default ASE parameters: Metric: 1 Tag: 1 Type: 2 Route Preference: 10 ASE Route Preference: 150 SPF Computation Count: 62 RFC 1583 Compatible Retransmission limitation is disabled Area Count: 1 Nssa Area Count: 0 ExChange / Loading Neighbors: 0 Process total up interface count: 1 Process valid up interface count: 1 Area: 0.0.0.20 Authtype: None Area flag: Normal SPF scheduled Count: 62 ExChange / Loading Neighbors: 0 Router ID conflict state: Normal Area interface up count: 1 Interface: x.y.z.1 (Vlanif3) Cost: 1 State: BDR Type: Broadcast MTU: 1500 Priority: 1 Designated Router: x.y.z.3 Backup Designated Router: x.y.z.1 Timers: Hello 10, Dead 40, Poll 120, Retransmit 5, Transmit Delay 1 OSPF Process 200 with Router ID x.y.z.17 OSPF Protocol Information RouterID: x.y.z.17 Border Router: AS Multi-VPN-Instance is not enabled Graceful-restart capability: disabled Helper support capability: not configured Spf-schedule-interval: max 10000ms, start 500ms, hold 1000ms Default ASE parameters: Metric: 1 Tag: 1 Type: 2 Route Preference: 10 ASE Route Preference: 150 SPF Computation Count: 53 RFC 1583 Compatible Retransmission limitation is disabled Area Count: 1 Nssa Area Count: 0 ExChange / Loading Neighbors: 0 Process total up interface count: 1 Process valid up interface count: 1 Area: 0.0.0.30 Authtype: None Area flag: Normal SPF scheduled Count: 53 ExChange / Loading Neighbors: 0 Router ID conflict state: Normal Area interface up count: 1 Interface: x.y.z.17 (Vlanif4) Cost: 1 State: DR Type: Broadcast MTU: 1500 Priority: 1 Designated Router: x.y.z.17 Backup Designated Router: x.y.z.19 Timers: Hello 10, Dead 40, Poll 120, Retransmit 5, Transmit Delay 1 The following is r0 configurations: interface Vlanif3 ip address x.y.z.1 255.255.255.240 ospf authentication-mode md5 1 cipher pass1 # interface Vlanif4 ip address x.y.z.17 255.255.255.240 ospf authentication-mode md5 1 cipher pass2 # ospf 100 router-id x.y.z.1 description business about bussiness1 default-route-advertise area 0.0.0.20 network x.y.z.0 0.0.0.15 # ospf 200 router-id x.y.z.17 description business about bussiness2 default-route-advertise area 0.0.0.30 network x.y.z.16 0.0.0.15 # ip route-static 0.0.0.0 0.0.0.0 q.w.e.r