MLAG Vs. vPC - How do they differ?

Constant innovation in IT and the introduction of new technologies are driving demand for faster speeds and higher bandwidths. To meet these demands, data center engineers are testing ways to connect the maximum number of network devices. Link Aggregation Group (LAG) is a solution that allows us to combine multiple Ethernet links into a single logical link to improve data transfer efficiency. Both vPC and MLAG enable the creation of LAGs, but each has advantages and disadvantages. Let's discuss vPC, MLAG and their differences.

What is MLAG?

The abbreviation MLAG stands for Multi-chassis Link Aggregation. MLAG is a non-standard protocol that provides multipathing at Layer 2 from the host to provide link resiliency and additional bandwidth. Through MLAG, we can bundle different ports from different switches to act and operate as a single logical link. Like stacking, MLAG allows multiple switches to operate as a single switch. It also brings physical diversity to the network by allowing a single host to uplink to two or more switches in a single bundle. These two switches can then be connected to two other switches using MLAG, with all links configured for forwarding. MLAG is available to all vendors and can be customized by anyone.

For MLAG connections, we typically use the LACP protocol (a subcomponent of 802.3ad) to negotiate south and north between MLAG virtual switches or between an MLAG virtual switch and a host. Switches that form an MLAG virtual switch, on the other hand, use proprietary east and west protocols.

LACP (Link Aggregation Control Protocol) provides methods for aggregating multiple physical connections into a single logical channel. In the event of a failed link, LACP mode allows other available link members participating in the same LACP group to share the load of the failed link. As a result, LACP-enabled connections can be more reliable and provide higher logical bandwidth.
 

Advantages of the MLAG

Below are some notable benefits of the MLAG;

• In MLAG, we can distribute the traffic evenly among the switches by using LAG hashing.
• MLAG allows multiple links to be bundled together to provide more east and west and north and south bandwidth.
• It provides stable operation with two levels of control and management.
• cAny switch participating in an MLAG can be upgraded without affecting the other devices and the network.
• MLAG makes it easy to expand port capacity by adding another switch either east or west.
• MLAG provides higher bandwidth connections to handle the increasing traffic on the network.
• To avoid loops, it supports STP operation.
• MLAG uses available bandwidth more wisely, with some connections blocked by STP

What is vPC?

Virtual Port Channel, or vPC, is a Cisco proprietary feature offered only for Cisco Nexus networking components. vPC enables Nexus devices to appear and operate as individual devices for endpoints or hosts. In the industry, vPC is also known as MEC (Multi-chassis EtherChannel).

How does vPC work?

Cisco vPC is a virtualization technology that allows two or more connected switches to appear and operate as a single port channel to any other endpoint. The endpoint can be a server, switch, or other network device such as a router or firewall. Through vPC, we can also create Layer 2 port channels with two switches.

Do non-Cisco switches support vPC?

Yes! Some third-party devices or switches support vPC, but we don't have many of them available on the market. It is difficult to configure a non-Cisco switch to follow vPC networking protocols. In this context, it is important to know that even Cisco's Catalyst series switches cannot be configured for vPC. Therefore, it is always better to use a Cisco Nexus series switch if you want to build a vPC network.

The following figure shows that inter-switch connections between two switches are established via vPC. A peer-to-peer connection between participating switches shares heartbeat messages with each other. The vPC domain contains vPC peer devices (switches), the vPC peer, and the keep-alive link. The port channels in the vPC domain connect to the downstream devices.

Advantages of vPC

vPC has many advantages, of which the following are just a few;

• It eliminates STP blocked ports
• vPC enables the creation of loop-free topologies
• vPC enables the use of the maximum available uplink bandwidth
• It ensures fast convergence in case of device or connection failure
• vPC provides unmatched resilience at the link level

MLAG vs. vPC: 4 main differences

Despite many similarities, vPC and MLAG also have some differences. Both vPC and MLAG can enable Layer 2 multipathing and create a port group between switches. In the vPC or MLAG domain, each group is configured and managed independently and can forward traffic without forwarding it to a master switch. 

Difficulties with implementation

MLAG is available worldwide as a public protocol and can be adapted by any manufacturer. On the other hand, vPC is specific only to Cisco's Nexus devices. Therefore, it is easier to implement MLAG than vPC.

Compatibility issues

For a vPC pairing, we need the same type of Cisco Nexus switches. Therefore, a vPC link cannot be established between a Nexus 5000 Series and a Nexus 7000 Series switch. Also, two vPC peers must be running the same version of NX OS to establish a vPC link.

Layer-Multipathing

A vPC peer link requires at least a few 10G Ethernet ports that are dedicatedly configured to operate in vPC mode. vPC is far superior to MLAG because it enables both Layer 2 and Layer 3 multipathing, allowing you to achieve maximum redundancy by ensuring multiple parallel routes between nodes. The availability of multiple paths ensures even network utilization. In addition, users can also use the MAGP protocol to enable Layer 3 multipathing with vPC.

Application scenarios

MLAG-compatible switches tend to form an MLAG pair at different levels. In general, vPC is only recommended for Cisco Nexus switches. In contrast, MLAG can be implemented in a variety of scenarios, including 2-tier spine-leaf architectures and 3-tier data center architectures. See the following diagram for a quick comparison between vPC and MLAG;

Conclusion

Both vPC and MLAG are recommended implementations for cloud computing and data center networks that require extreme network reliability and bandwidth.

MLAG takes advantage of link aggregation to provide network-level resiliency and system-level redundancy.

First and foremost, before choosing vPC or MLAG, analyze your network equipment and its capabilities. Not every switch supports MLAG, and only Cisco Nexus switches can support vPC. Later, depending on your network requirements and fabric architecture, you can proceed with either vPC or MLAG to make an appropriate decision.