Switch Basics: Link Aggregation technology

Switch Basics: Link Aggregation definition

Link aggregation technology is also known as backbone Technology (trunking) or bundled technology (bonding), its essence is to two devices between several physical link "combination" into a logical data path, called an aggregation link, such as Figure1 signal. Physical links between switches Link1, LINK2, and Link3 form an aggregation link. The link is logically a whole, and the details of the internal composition and transmission data are transparent to the upper service.

▲ Link Aggregation schematic diagram

The physical link within the aggregation completes the data sending and receiving tasks together and backs up each other. As long as there are still working members, the entire transmission link will not fail. Still, for example, if Link1 and Link2 fail, their data tasks are quickly transferred to the LINK3, so the connection between the two switches is not interrupted (see FIGURE2).

▲ Link aggregation members are backed up with each other

Switch Basics: The benefits of link aggregation

As you can see from the above, link aggregation has some notable advantages:

1. Improve link availability

In link aggregation, members are dynamically backed up by each other. When a link is interrupted, other members can quickly take over their work. Unlike the spanning tree protocol, link aggregation enables backup processes that are not visible outside of aggregations, and enabling the backup process is only within the aggregation link, independent of other links, and switches can be completed in milliseconds.

2. Increase link capacity

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Another obvious advantage of the link aggregation technology is to provide users with an economical way to improve the link transmission rate. By bundling more than one physical link, a user can obtain a larger bandwidth data link without upgrading the existing device, which equals the sum of the physical link capacity. The aggregation module assigns traffic flow to different members according to some algorithms, and realizes the load sharing function of link level.

In some cases, link aggregation is even the only way to increase the link capacity. For example, when the market equipment can not provide more than 10G link, users can be two 10G link aggregation, to obtain bandwidth greater than 10G transmission lines.

In addition, the specific network environment needs to limit the transmission line capacity, neither too low impact transmission speed, nor too high over the network processing capacity. But the existing technology only support the link bandwidth to 10 for the order of magnitude growth, such as 10M, 100M, 1000M and so on. And through the aggregation of the N physical link bundle up, you can get more appropriate, n times bandwidth of the link.

Switch Basics: Standard for link aggregation

The formal standard for the current link aggregation technology is IEEESTANDARD802.3AD, which is formulated by the IEEE802 Commission. The target of link aggregation technology, the function and operation principle of each module in the aggregation sub layer, and the content of link aggregation control are defined in the standard.

Among them, the goal of aggregation technology should be to improve link availability, linearly increase bandwidth, share load, realize automatic configuration, fast convergence, ensure transmission quality, transparent to the upper level users, backward-compatible and so on.

Switch Basics: Link Aggregation Control Protocol LACP

Link Aggregation Control Protocol (LINKAGGREGATIONCONTROLPROTOCOL) is one of the main contents of IEEE802.3AD standard, and defines a standard aggregation control method. Aggregation of the two devices through the protocol interactive aggregation of information, according to the parameters and state of both sides, the matching link is automatically aggregated together to send and receive data. After the polymerization is formed, the switching equipment maintains the aggregation link state and automatically adjusts or dissolves the aggregation link when the two configurations change.

The aggregation information in the LACP protocol packet includes the configuration parameters and aggregation status of the device, and the message sending mode is divided into event triggering and cycle sending. When the aggregation state or configuration change event occurs, the system notifies the client of its own change by sending a protocol message. When the polymerization link works stably, the system switches the current state to maintain the link. The protocol message does not carry the serial number, so both parties do not detect and re-send the Lost protocol message.

In the link aggregation, it is necessary to point out that the LACP protocol is not equal to the link aggregation technology, but a link aggregation control method provided by Ieee802.3ad, and other polymerization control methods can be used in the implementation.