Link aggregation is a computer networking term to describe various methods of combining (aggregating) multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide redundancy in case one of the links fail.
Further umbrella terms used to describe the method include port trunking,link bundling,Ethernet/network/NIC bonding, or NIC teaming. These umbrella terms not only encompass vendor-independent standards such as Link Aggregation Control Protocol (LACP) for Ethernet defined in IEEE 802.1ax or the previous IEEE 802.3ad, but also various proprietary solutions.
Initial release 802.3ad in 2000
As of 2000 most gigabit channel-bonding schemes use the IEEE standard of Link Aggregation which was formerly clause 43 of the IEEE 802.3 standard added in March 2000 by the IEEE 802.3ad task force.[4] Nearly every network equipment manufacturer quickly adopted this joint standard over their proprietary standards.
Move to 802.1 layer in 2008
David Law noted in 2006 that certain 802.1 layers (such as 802.1X security) were positioned in the protocol stack above Link Aggregation which was defined as an 802.3 sublayer. This discrepancy was resolved with formal transfer of the protocol to the 802.1 group with the publication of IEEE 802.1AX-2008 on 3 November 2008.
Reference Diagram - Link Aggregation between Server and Switch
Types of Link Aggregation:
1. Static Link Aggregation
With a static link aggregate, all configuration settings will be
setup on both participating LAG components.
2. Dynamic Link
Aggregation: Link Aggregation Control Protocol (LACP)
Beyond that, Link Aggregation Control Protocol (LACP) allows the
exchange of information with regard to the link aggregation between the two
members of said aggregation. This information will be packetized in Link
Aggregation Control Protocol Data Units (LACDUs).
Each individual port can be configured as an active or passive
LACP using the control protocol.
·
Passive LACP: the port
prefers not transmitting LACPDUs. The port will only transmit LACPDUs when its
counterpart uses active LACP (preference not to speak unless
spoken to).
·
Active LACP: the port
prefers to transmit LACPDUs and thereby to speak the protocol, regardless of
whether its counterpart uses passive LACP or not (preference
to speak regardless).
In contrast to a static
link aggregation, LACP provides the following advantages:
·
Even if one physical
links fails, it will detect if the point-to-point connection is using a media
converter, so that the link status at the switching port remains up.
Because LACPDUs do not form a component of this connection, the link will be
removed from the link aggregate. This ensures that packets will not be lost due
to the failed link.
·
Both of the devices can
mutually confirm the LAG configuration. With static link aggregation, errors in
the configuration or wiring will often not be detected as quickly.
MC-LAG
MC-LAG adds node-level redundancy to the normal link-level redundancy that a LAG provides. This allows two or more nodes to share a common LAG endpoint. The multiple nodes present a single logical LAG to the remote end. Note that MC-LAG is vendor-specific; it is not covered by the IEEE 802.1AX-2008 standard. Nodes in an MC-LAG cluster communicate to synchronize and negotiate automatic switchovers (failover). Some implementations may support administrator-initiated (manual) switchovers.
MC-LAG, or Multi-Chassis Link Aggregation Group, is a type of LAG with constituent ports that terminate on separate chassis, thereby providing node-level redundancy. Unlike link aggregation in general, MC-LAG is not covered under IEEE 802.1AX-2008. Its implementation varies by vendor.
IEEE 802.1AX Link Aggregation (LAG) technology has solved this using multipathing at Layer 2 and flow-based load balancing. However, the protocol constrains the network to a node-to-node topology. Organizations require a Layer 2 multipath solution that can provide dynamic flow-based load balancing to multiple network nodes. MC-LAG is designed to address these requirements for today’s resilient and high-performance networks.
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