Hello, everyone!
Today, I'd like to share a case with you.
Problem Description：
A customer reports the ONT HG8040H LAN1 upstream traffic reaches 900MB/S while there is no downstream traffic, LAN 3 downstream reaches 900MB/s while no upstream traffic.
Problem Analysis：
1. The ONT LAN1 port has a large amount of traffic with input direction, and it is all multicast and broadcast traffic, but there is no traffic with output direction.
2. The ONT LAN 3 has a few groups broadcast with input direction, and there are a lot of multicast and broadcast traffic with output direction and they should come from LAN1 input direction.
3. When we try to disable the ONT LAN3 port through the U2000, the traffic of the LAN1 port, the LAN3 port and the PON port becomes 0.
4. When we try to enable the ONT LAN3 port through U2000, the fault phenomenon recovers again.
Root cause：
1.The message of LAN1 input port direction of the VLAN will be forwarded to LAN3, which will be copied and sent to ONT PON output port, so the traffic of ONT PON output port direction and that of ONT LAN1 input port direction were the same, which is near 1Gbps;
2.After the message of LAN1 input port the direction is forwarded to VLAN 1, and as the message is multicast and broadcast, it will be copied to the corresponding interface based on the VLAN 1 domain, because the LAN3 port exists C-VLAN 3 switch to S-VLAN 1, so the LAN3 port is just in the VLAN 1 domain, the multicast and broadcast that led to the entry from LAN 1 will replicate a copy from the LAN3 output direction, so causes the LAN3 output direction traffic and the LAN1 input direction traffic were the same, near 1Gbps.
Connection with ONT Equipment Network there is a loop, so from the LAN3 output direction of the message and back into the LAN1 port, resulting ina greater flow of traffic.
Solution Description：
It is recommended to check on-site to learn the customer’s network and physical connection, and whether there is a physical loop and how it becomes a loop.
Thanks.
