Traffic is not forwarded through all member interfaces of an Eth-Trunk in a stack. Why

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When a stack device forwards traffic, an Eth-Trunk may select a member interface of another stack device through the hash algorithm, which occupies bandwidth resources between stack devices and reduces the traffic forwarding efficiency. To address the preceding problem, run the local-preference enable command to enable the Eth-Trunk to preferentially forward local traffic. That is, traffic arriving at the local device is preferentially forwarded through member interfaces of the local device. If the local device has no member interface, the member interface of another stack device is used to forward traffic. This saves bandwidth resources between stack devices and improves the traffic forwarding efficiency.

By default, an Eth-Trunk is enabled to preferentially forward local traffic. Before configuring an Eth-Trunk to preferentially forward local traffic, ensure that the outbound bandwidth of Eth-Trunk member interfaces is sufficient for forwarding local traffic. If the outbound interface bandwidth is insufficient, some packets are dropped.

Other related questions:
Number allocation of Eth-Trunk member interfaces on stacked S series switches
After you configure an Eth-Trunk on stacked S series switches (except the S1700), the member interface number remain unchanged even if you split the stack and stack the switches again.

Why does traffic forwarding fail when the switch is connected to another device through an Eth-Trunk
After an Eth-Trunk is configured on the switch, the manual load balancing mode is adopted on the Eth-Trunk by default. If the device connected to the switch uses the static LACP mode after link aggregation is configured, the two devices use different working modes at two ends of the Eth-Trunk. As a result, traffic cannot be transmitted on the Eth-Trunk. To ensure traffic transmission on the Eth-Trunk, you need to set the same working mode on the two devices.

How to determine the number of member interfaces in an Eth-Trunk
To ensure normal forwarding of burst traffic on an Eth-Trunk, the total bandwidth of the Eth-Trunk must be higher than the bandwidth of an interface that forwards normal traffic. To ensure that member interfaces of an Eth-Trunk evenly load balance traffic, you can use two, four, or eight member interfaces.

Why does traffic forwarding fail when an S series switch is connected to another device through Eth-Trunk
After Eth-Trunk link aggregation is configured for an S series switch (except the S1700), the Eth-Trunk works in manual load balancing mode by default. If Eth-Trunk link aggregation is also configured for the peer device, the Eth-Trunk works in LACP mode by default. The two ends of the Eth-Trunk work in different default modes, resulting in forward traffic failure. To ensure normal traffic forwarding, you must configure the same working mode for the two ends.

Traffic is not passing through ETH trunk in LAG configuration?
STP is enabled by default, check the ports status to see if they are blocked.

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