What's the Difference Between MLAG and vPC?

Today, more and more enterprises are leveraging data center virtualization to reduce costs and streamline data flows, and network capacity requirements will increase significantly to ensure that data can be seamlessly transferred between data centers and business locations. To keep up with this trend, the industry is looking for ways to increase network capacity by connecting as many network devices as possible, such as MLAG and vPC, two link aggregation technologies that connect multiple Ethernet switches and increase network capacity. So do you know about them? What is the difference between the two? This article will provide a comprehensive overview.

What is MLAG?

MLAG (Multi-Chassis Link Aggregation) is a non-standard protocol that enables Layer 2 multipathing from hosts for additional bandwidth or link resiliency, and because it is a public protocol, each vendor can customize mechanisms to implement support for MLAG. MLAG is the aggregation of two or more switches across device links to form an M-LAG dual-host system, meaning it allows two or It allows two or more physical switches to present a parallel set of links as a single aggregated link, and allows hosts to uplink to both switches for physical diversity while managing only one bundled interface. In turn, these two switches can use MLAG to connect to other switches and forward all data.

In MLAG links, the Link Aggregation Control Protocol (i.e., LACP) is typically used for north-south negotiation between hosts and MLAG virtual switches or between MLAG virtual switches. A proprietary east-west protocol is used between switches belonging to the same MLAG duplex system. In Figure 1 below, multiple Ethernet switches are used to form an MLAG duplex system. In this case, the four leaf switches in the MLAG duplex system establish redundant connections from the servers to the switches, and the LAG groups rely on static link aggregation or LACP protocol-based negotiation methods.


Figure 1: MLAG dual-active system

Advantages of MLAG

● Distributing traffic evenly to each switch through the use of LAGs.
● Increasing the bandwidth available for north-south and east-west traffic by simply bundling more links into LAG groups.
● Providing stability through dual management and control planes.
● Support for upgrading one switch at a time, without affecting other devices.
Expanding port capacity is simple and free - system ports can be expanded by creating another MLAG duplex system to another switch to add another switch for east-west transport.

What is vPC?

vPC (or Virtual Link Aggregation) is a Cisco Nexus Series-specific technology that is difficult to configure on other types of switches. Of course this is not absolute, and there are some vendors other than Cisco that offer switches with vPC support. So what exactly is vPC? vPC technology allows a physical link to two different Cisco switches to be treated as a logical port aggregation link to other devices (such as switches, servers, or any other network device that supports IEEE 802.3ad PortChannels). vPC can allow Layer 2 PortChannels (i.e. PortChannels) to be created across two switches, as shown in the figure below. vPC is used to create inter-switch links across two switches while, at the same time, keeping the two control planes of those switches separate. With vPC enabled, you need to create a peer-to-peer keepalive link for sending heartbeats between devices. vPC domains contain the vPC end device, the vPC peer-to-peer keepalive link, the vPC peer-to-peer interconnect link, and all PortChannels under the vPC domain. Note: Only a maximum of one vPC domain can be specified on each device.


Figure 2: vPC working topology diagram

Advantages of vPC

● Allowing a device to connect to two different upstream devices with a PortChannel.
● Eliminating Spanning Tree Protocol blocking ports.
● Providing a loop-free topology.
● All available upstream bandwidth can be used.
● Enables fast convergence, faster than spanning tree, when a link or device fails.
● Providing link-level resiliency.
● Helps ensure high availability.

What is the Difference Between MLAG and vPC?

As you can see above, both MLAG and vPC can be used to create port groups between two switches and can provide Layer 2 multipathing options. In an MLAG duplex system or vPC domain, each switch is independently managed and configured to forward/route traffic without having to transmit through the primary switch. So what is the difference between MLAG and vPC?

Obviously, the biggest difference between them is the difficulty of implementation. MLAG is a public protocol and almost every vendor can use custom mechanisms to implement support for MLAG, while vPC is a Cisco Nexus-specific protocol and not all vendors can use the technology; therefore MLAG is relatively easier to install than vPC. Network engineers who want to deploy vPC should study the vendor vPC design guidelines before building a vPC domain, and when configuring vPC, they must ensure that they are using the same family of Cisco Nexus switches, such as configuring vPC on a Nexus 7000 series or Nexus 5000 series switch, but not on a Nexus 7000 series and Nexus Also, the vPC-side switches must be running the same NX-OS version (except for non-disruptive upgrades). In addition, the vPC end-to-end link must be a minimum of two 10G Ethernet interfaces.

vPC is more advanced than MLAG. vPC can support both Layer 2 and Layer 3 multipathing, enabling users to add network redundancy with multiple optional paths, while enabling multiple parallel paths between multiple nodes and load balancing traffic with enhanced bandwidth. To enable Layer 3 multipathing, use the dual-active gateway protocol (MAGP). Typically, vPC is used for data center (Nexus appliances running NX-OS or ACI mode) switches, while MLAG can be used for most distributed applications or data center switches.

Summary

Both MLAG and vPC are ideal technologies and easy to implement for data center and cloud networks with higher network bandwidth and reliability requirements. MLAG takes advantage of link aggregation by distributing it across a pair of data center switches, thus providing higher redundancy and enabling highly resilient multipath networks. vPC is more suitable for non-blocking path diversity, where virtual machines may be located any given location. Whether you choose MLAG or vPC, you need to find out whether your network equipment can support MLAG or vPC before deciding which feature to configure in conjunction with your network architecture and your specific business traffic needs.