Classification of Eth-Trunks on S series switches


Eth-Trunks can work in manual load balancing mode or LACP mode.
Eth-Trunk in manual load balancing mode:
The manual load balancing mode is a basic link aggregation mode. In this mode, you must manually create an Eth-Trunk, add member interfaces to the Eth-Trunk, and specify active member interfaces. This mode does not involve LACP. All active interfaces forward data and evenly share load. If an active link fails, the remaining active links automatically share the traffic evenly.
Eth-Trunk in LACP mode:
In LACP mode, you must manually create an Eth-Trunk and add member interfaces to the Eth-Trunk. Different from the Eth-Trunk in manual load balancing mode, active member interfaces in LACP mode are selected using LACP protocol packets. When a group of interfaces are added to an Eth-Trunk, the devices at both ends determine active interfaces and inactive interfaces through the LACP packets.
The LACP mode is also called M:N mode. This mode supports both load balancing and redundancy backup functions. In the link aggregation group, M links are active links responsible for data forwarding and load balancing, whereas N links are inactive links working as backup links and do not forward data. If an active link becomes faulty, the system selects the link with the highest priority from the N inactive links to replace the faulty link. The inactive link becomes active and starts to forward data.

Other related questions:
License classification on S series switch
Licenses are classified as follows: Depending on purpose, licenses are classified into commercial (COMM) licenses and non-commercial (DEMO) licenses. Commercial license Generally, these licenses are purchased according to contracts, and are permanently valid. Non-commercial license These licenses are used for special purposes such as testing and trial, and are strictly controlled. Depending on authority, licenses are classified into feature licenses and capacity licenses. Feature license License-controlled features cannot be used without a license. An enhanced feature takes effect only after the value-added feature or another enhanced feature it depends on takes effect. Therefore, both the license for the enhanced function and the license for the dependent function must be installed. Capacity license These licenses are used to expand dynamic resources on the product. A capacity license takes effect only after the corresponding feature takes effect. If the feature is a license-controlled one, the license for the feature must be loaded before the capacity license. Customers can choose not to purchase a capacity license and use the default number of resources supported by the product, or purchase one or more licenses to obtain the total number of resources supported by the purchased licenses.

The difference between E-trunk and Eth-Trunk on S series switches
For S series switches (except the S1700): Eth-Trunk, also called link aggregation, bundles multiple physical links to form a logical link to increase link bandwidth. The bundled links can enhance link reliability through mutual backup. E-Trunk (Enhanced Trunk), developed from LACP (a link aggregation protocol for a single device), is a mechanism that implements link aggregation among multiple devices. E-Trunk achieves device-level link reliability, instead of card-level link reliability previously achieved by LACP.

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.

Link aggregation support on S series fixed switches
S series fixed switches (except the S1700) support the link aggregation function. For details about link aggregation support on the fixed switches, see the "Ethernet Switching - Link Aggregation" in the S1720&S2700&S3700&S5700&S6700 Product Use Precautions.

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