How load balancing is implemented on S series switches when link aggregation is configured

For S series switches (except the S1700), there are two load balancing modes: per-packet load balancing and per-flow load balancing.
1. Per-packet load balancing mode
When there are multiple physical links between the two devices of the Eth-Trunk, the first data frame of a data flow is transmitted on one physical link, and the second data frame is transmitted on another physical link. In this case, the second data frame may arrive at the peer device earlier than the first data frame. As a result, packet mis-sequencing occurs.
2. Per-flow load balancing mode
This mechanism uses the hash algorithm to calculate the address in a data frame and generates a hash key value. Then the system searches for the outbound interface in the Eth-Trunk forwarding table based on the generated hash key value. Each MAC or IP address corresponds to a hash key value, so the system uses different outbound interfaces to forward data. This mechanism ensures that frames of the same data flow are forwarded on the same physical link and implements flow-based load balancing. Per-flow load balancing ensures the correct sequence of data transmission, but cannot ensure the bandwidth usage.
Notes: Currently, S series switches support only per-flow load balancing mode, including the following:

1. Load balancing based on the source MAC address of packets;
2. Load balancing based on the destination MAC address of packets;
3. Load balancing based on the source IP address of packets;
4. Load balancing based on the destination IP address of packets;
5. Load balancing based on the source and destination MAC addresses of packets;
6. Load balancing based on the source and destination IP addresses of packets;
7. Enhanced load balancing for L2, IPv4, IPv6, and MPLS packets based on the VLAN ID and source physical interface number.
When you configure load balancing modes, follow these guidelines:
The load balancing mode only takes effect on the outbound interface of traffic. If load is unevenly distributed on the inbound interfaces, change the load balancing mode on the uplink outbound interfaces.
Configure load balancing to ensure data flow is transmitted on all active links instead of only one link, preventing traffic congestion and ensuring normal service operation.
For example, if data packets have only one destination MAC address and IP address, you are advised to configure load balancing based on the source MAC address and IP address. If you implement load balancing based on the destination MAC address and IP address, the data flow may be transmitted on only one link, causing traffic congestion.

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