Principles of AP load balancing

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Load balancing can evenly distribute AP traffic loads to ensure high bandwidth for each STA. The load balancing function applies to wireless networks with high user densities to ensure proper access of STAs.

Depending on whether a load balancing group needs to be manually created, load balancing is classified into static and dynamic load balancing. For details about the principles, see:

V200R005:

Configuring Load Balancing

V200R006:

Configuring Load Balancing

Other related questions:
Do Fat APs support load balancing
Fat APs do not support load balancing. Load balancing is supported only in AC+Fit AP architecture.

AP load balancing does not take effect
To implement load balancing, the following requirements must be met; otherwise, configurations fail or do not take effect. 1. The requirements for a radio to join a load balancing group are as follows: - A radio can join only one load balancing group. - The newly added radios must be of the same type as other radios in the load balancing group. Radios in a hotspot area must be of the same type. Otherwise, load balancing cannot be achieved. The type of radios in a load balancing group is determined by the type of the first added radio. - The channel of a new radio must be different from channels of other radios in the load balancing group. If the channel of a new radio is the same as channels of other radios in the load balancing group, a radio signal collision occurs. To improve coverage areas and minimize collisions, APs in a hotspot area must be configured with different channels. To detect channel collisions, check the configured channel and actual channel of the radio. - More radios can be added to a load balancing group if it is not full. In a load balancing group, radios must be configured with different channels and all these radios must be of the same type. In addition, radios of the same type support limited and fixed channels. Therefore, the number of radios in a load balancing group is limited. 2. The load balancing function applies to scenarios where there is a high degree of overlapping between APs' coverage ranges. You can adjust the AP power to enable the APs' coverage areas to overlap. When the load difference between APs reaches the load difference threshold, some STAs may access the network slowly, because the APs will reject access requests of STAs according to the load balancing algorithm. If a STA continues to send association requests to an AP, the AP allows the STA to associate when the number of consecutive association attempts of the STA exceeds the maximum number of rejection times.

Load balancing principle of Eth-Trunk member interfaces on CE switches
An Eth-Trunk has 16 timeslots for sending packets at each interval. Eth-Trunk member interfaces use the 16 timeslots to send packets in sequence. When the number of Eth-Trunk member interfaces is the nth power of 2, load balancing can be made more even. For example, if the number of Eth-Trunk member interfaces is 2, 4, or 8 (which is divisible by 16), the timeslot of the packets sent by each interface is an integer, making load balancing even. If it is not the nth power of 2 (for example, 3), a member interface gets 6 times for sending packets from 16 timeslots, while the other two only get 5 times. In this way, load balancing is not even. Therefore, you are advised to set the number of Eth-Trunk member interfaces to the nth power of 2, ensuring even load balancing.

Load balancing
The functions and meanings of load balancing are described as follows: When multiple routes have the same routing protocol preference and metric, these routes are called equal-cost routes, among which load balancing can be implemented. Routers support the multi-route mode, allowing you to configure multiple routes with the same destination and preference. If the destinations and costs of multiple routes discovered by the same routing protocol are the same, load balancing can be performed among the routes. Run the maximum load-balancing number command in the views of various protocols to implement load balancing. Load balancing falls into the following two modes: -Packet-by-packet When the packet-by-packet load balancing is configured, firewalls at the network layer forward packets to the same destination through various equal-cost paths. That is, switches always choose the next hop address that is different from the last one to send packets. -Session-by-session When session-by-session load balancing is configured, firewalls forward packets according to the source address, destination address, source port, destination port, and protocol contained in the packets. When the five factors are the same, firewalls always choose the same next hop address as the last one used to send the packets.

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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