Hello, friend!
Layer 3 forwarding uses routing information to forwarding packets. The next-hop IP address is found based on the destination IP address of packets, and the corresponding egress is found based on the ARP of the next-hop IP address. In principle, Layer 2 forwarding learning and searching are not required.
For the MA5800, the distributed forwarding architecture is adopted. During Layer 3 forwarding, the control board does not need to learn the MAC address of the user. The corresponding egress can be found by learning routes and ARP entries.
For the MA5680T, Layer 3 route forwarding is implemented on the LSW. Because the LSW adopts the centralized forwarding architecture, during Layer 3 forwarding, the LSW needs to learn the MAC address of the user to find the corresponding board.
According to your problem description, the possible causes of the failure of the MA5800 to learn MAC addresses are as follows:
1. ICMP packets are forwarded at Layer 3 through a VLANIF interface. The MA5800 does not learn MAC addresses for Layer 3 forwarding packets.
2. When the MA5800 pings the peer end, the ARP packets sent by the MA5800 are captured by the CPU and forwarded at Layer 2. In this case, the MA5800 learns MAC addresses. After the ARP packets are learned, the packets are forwarded at Layer 3. After 300 seconds (the MAC address aging time configured in the system is 300 seconds), the MAC address is aged out.
3. If an ARP entry has been learned but the MAC address has been aged, the peer device can be pinged but the MAC address has not been learned because only Layer 3 forwarding is available.
Thanks!
