Basic vswitch knowledge: link aggregation technology

Vswitch basics: Definition of link Aggregation

Link aggregation technology (also known as Trunking) or bundling technology Bonding) is essentially a logical data path that combines several physical links between two devices, it is called an aggregation link, as shown in Figure1. The physical links Link1, Link2, and Link3 between vswitches form an aggregation link. The link is logically integrated. The internal composition and data transmission details are transparent to upper-layer services.

Link Aggregation

Aggregate physical links to complete data sending and receiving tasks and back up each other. As long as there are still Members that can work normally, the entire transmission link will not become invalid. Link aggregation is still used as an example. If Link1 and Link2 fail successively, their data tasks will be quickly transferred to Link3, so the connection between the two switches will not be interrupted. See Figure2 ).

Link aggregation members backup each other

Vswitch basics: Advantages of link Aggregation

As shown above, link aggregation has the following significant advantages:

1. Improve link availability

In link aggregation, members dynamically back up each other. When a link is interrupted, other members can take over quickly. Different from the Spanning Tree Protocol, the process of enabling backup for Link aggregation is invisible outside of aggregation, and the backup process is only within the aggregation link, which is irrelevant to other links, the switchover can be completed within several milliseconds.

2. Increase link capacity

Another obvious advantage of The Link aggregation technology is to provide users with an economical method to improve the link transmission rate. By bundling multiple physical links, you do not need to upgrade existing devices to obtain a data link with larger bandwidth. The capacity is equal to the sum of the capacity of each physical link. The aggregation module allocates service traffic to different members based on certain algorithms to achieve load balancing at the link level.

In some cases, link aggregation is the only way to increase the link capacity. For example, if no device on the market can provide a link larger than 10 Gbit/s, you can aggregate two 10 Gbit/s links to obtain a transmission line with a bandwidth greater than 10 Gbit/s.

In addition, the capacity of transmission lines needs to be limited in a specific networking environment, which neither affects transmission speed nor exceeds the processing capability of the network. However, existing technologies only support the increase of link bandwidth by 10, such as 10 M, 100 M, and M. By aggregating and bundling n physical links, we can get a more suitable link with n times of bandwidth.

Basic switch: Standard for Link Aggregation

The formal standard of link aggregation technology is IEEEStandard802.3ad, which is developed by the IEEE802 committee. The standards define the objectives of The Link aggregation technology, the functions and operation principles of each module in the aggregation sub-layer, and the content of link aggregation control.

Where, the goal of aggregation technology is to improve link availability, linearly increase bandwidth, share load, achieve automatic configuration, fast convergence, ensure transmission quality, be transparent to upper-level users, and be backward compatible..

Vswitch basics: LACP

Link aggregation Control Protocol (LinkAggregationControlProtocol) is one of the main contents of the IEEE 802.3ad standard. It defines a standard aggregation control mode. The devices of both Parties exchange and aggregate information through the Protocol. Based on the parameters and status of both parties, the matching links are automatically aggregated to send and receive data. After aggregation, the switching device maintains the state of the aggregation link. When the configurations of both parties change, the aggregation link is automatically adjusted or disband.

The aggregation information in LACP packets includes the configuration parameters and aggregation status of the device. The message transmission methods include event trigger and periodic transmission. When an aggregation status or configuration change event occurs, the system sends a protocol message to notify the peer of its changes. When the aggregation link works stably, the system regularly switches the current status to maintain the link. Protocol packets do not carry serial numbers, so both parties do not detect and resend lost protocol packets.

In link aggregation, LACP is not equivalent to link aggregation technology, but a link aggregation control method provided by 802.3ad. Other aggregation control methods can also be used in specific implementation.