Why EGS4 prevents LACP protocol packets from being transparently transmitted?

 Problem Description

The link aggregation function is activated between two switches in a certain office. One port uses the dedicated line service configured by EGS4 and EGS2 of OSN3500, and the other port uses optical fiber to connect directly. When the switch starts manual aggregation (without LACP protocol), the service is normal. But when it is configured as static aggregation (LACP protocol is started), the service fails. The attributes of the external ports of the EGS4 and EGS2 boards are Hybrid. The switch on the EGS4 side can receive LACP packets, but the EGS2 switch cannot receive LACP packets.

Warning message

No abnormal transmission alarm

Process

1. Since the business is normal when using manual aggregation, it is certain that there is no problem with the transmission channel.

2. The difference between static aggregation and manual aggregation is that it uses the LACP protocol. Therefore, when static aggregation is suspected, the cause of service failure is that LACP protocol packets are not transparently transmitted to the peer device.

3. The LACP protocol does not have a VLAN tag. It should be no problem if the port attribute is set to Hybrid. It is suspected that the ingress port of the egs4 board does not transparently transmit LACP packets.

4. After confirming that the egs4 board supports the LACP protocol, when the external port receives the LACP message, it will be sent to the CPU for processing instead of transparently transmitting the LACP message. In this case, you need to set the port's "ingress detection" function as "Prohibited"

5. The static link aggregation service of the switch is normally opened after setting the "ingress detection" of the port

Root cause

1. The EGS4 board supports the LACP protocol. When the external port receives the LACP message, it will be sent to the CPU for processing and will not transparently transmit the LACP message. If the LACP message needs to be transparently transmitted, it is necessary to set the port's "ingress detection" "The function is "Prohibited".

2. The EGS2 board port does not support the LACP protocol, and treats LACP packets as ordinary Ethernet packets, so LACP packets can be detected in one direction.

Conclusions

At the same time, I learned that SSN5EFS0 also has this problem. When you need to transparently transmit LACP packets, you need to pay attention to the "ingress detection" attribute configuration.