Difference of LAG,LACP and MLAG
Regardless of whether it's a conventional data center or a modern cloud-based data center, the universal necessity is high availability, and a prevalent issue is the potential single point of failure within the network. In traditional physical networking, to establish highly dependable connections between various devices, LAG (Link Aggregation) technology was developed to ensure high availability of links between servers and switches or even between multiple switches. However, LAG technology possesses its own flaws and is unable to eliminate the risk of equipment failure entirely.
Thus, a more advanced technology is required to broaden the original one-to-one connection between devices into a one-to-many connection while ensuring multi-device redundancy and multi-link redundancy. It must also guarantee that devices are able to interconnect with optimal robustness. Introducing MC-LAG, an enhancement of the traditional LAG technology. To accurately comprehend the workings of MC-LAG, it is necessary to first understand the principles behind LAG itself.
What Is MC-LAG?
MC-LAG extends the original link aggregation technology from one-to-one devices to one-to-many devices, as depicted in the illustration below.
With node redundancy in place, traffic is appropriately load-balanced between two switching devices using a hash algorithm. Additionally, MC-LAG has a built-in anti-loop mechanism, eliminating the need for complex STP protocols or Layer 3 routing and forwarding configurations. This simplifies network configuration complexities.
MC-LAG relies on the LACP protocol’s working mechanism to achieve cross-device link redundancy. When negotiating with two switches, it needs to present itself as a single device in the LAG scenario. To accomplish this illusion, the system IDs of LACP packets within the cross-device redundant links must match; that is, SwitchA’s system ID during negotiation with the server must be identical to SwitchB’s system ID. This concept forms the foundation for MC-LAG’s ability to implement cross-device link aggregation.
MC-LAG Failure Scenario&Traffic Forwarding Paths
As depicted in the diagram below, ServerA and ServerB are linked to the access switch via MC-LAG. In normal circumstances, traffic transmitted from ServerA to ServerB follows the forwarding path indicated by the green line, which defaults to Switch A.
If the connection between ServerB and SwitchA fails, either due to the physical port linking ServerB to SwitchA or the physical port linking SwitchA to ServerB, the forwarding path of the traffic from ServerA to ServerB changes, represented by the brown line.
If SwitchA encounters a device failure, SwitchB takes over the forwarding of traffic from ServerA to ServerB, following the route demonstrated by the red line.
If a PeerLink fault occurs, the traffic sent from ServerA to ServerB remains forwarded via the green path.
Application Scenarios Of MC-LAG
Networking Solution 1: MC-LAG At the Aggregation Layer :Through the cross-device port virtualization technology (MC-LAG), the network logic between the aggregation layer and the access layer switch is realized without looping, replacing STP. Compared with the traditional STP breakpoint protection, this design has a clearer logical topology and more efficient link utilization. For MC-LAG paired devices, the control plane and management plane are independent, and only the protocol plane is coupled. In theory, the reliability is higher than that of stacking. It also provides the ability to upgrade devices independently, bringing convenience to maintenance.
Networking Solution 2: Establishing MC-LAG at the Access Layer:The same MC-LAG technology is applicable to the application scenario where dual network cards of the server require active-active access. The server is dual-active connected to the two NICs to share the MAC. Dual NICs implement a flow-based load sharing strategy. Therefore, configure the port connected to the server as a member port of MC-LAG through MC-LAG, and the MAC and ARP entries of the two ports will be synchronized in real time.
As a cross-device link aggregation technology, M-LAG not only has the advantages of increasing bandwidth, improving link reliability, and load sharing, but also has the following advantages:
- Enables simpler network design: With M-LAG, multiple switches can be treated as a single logical device, simplifying the network design and reducing management complexity.
- Provides faster failover and better network stability: M-LAG provides rapid failover and increased network stability, reducing downtime and improving overall network performance.
- Offers more flexible deployment options: M-LAG can be deployed at different layers of the network stack and is compatible with different devices from different vendors, making it a more flexible option than some other link aggregation technologies.
- Improves scalability: M-LAG can improve the scalability of network links, allowing for the addition of more devices and increased bandwidth without sacrificing network performance.
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