Topology: One AR46-80 router connects to a switch.
Symptoms: Mutual ping flaps in test when both devices are connected.
Check the configuration of router, and no problem is found. According to the symptoms, the port mode is suspicious of problematic. Check the port mode of both sides, and it is 10/100 auto-negotiation, and it is 100Mbit/s at all. Check the network cables at last, and it is found that they are not made according to the standard wiring sequence; make the cables according to the standard wiring sequence, and the problem is solved. Services are restored.
The direct network cables between the router and switch have the same wiring sequence simply, and they are not standard, or both sides are not orange+white, orange, green+white, blue, blue+white, green, brown+white, brown. Such network cables do not have good performance physically.
Quality of Network cables may result in a lot of problems. So Make the network cables according to the standard.