MLAG vs VPC: What's the Difference?
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MLAG vs VPC: What’s the Difference?

Posted on by FS.COM

As more enterprises begin to utilize data center virtualization to cut costs and streamline data flows, the demand for more network bandwidths increases substantially to ensure that data can be transferred seamlessly between data center and business locations. To cater for this trend, network engineers are seeking for ways to connect as many networking devices as you can to enhance network capacity. MLAG and VPC are new technologies to connect multiple fiber switches. What do these terms mean and how they differ from each other? This post will give an overall explanation for each of them, and set out how to make a proper decision over MLAG vs VPC.

What Is MLAG?

MLAG (Multi-chassis Link Aggregation) is a non-standard protocol that enables Layer 2 multipathing from the host to gain either additional bandwidth or link resiliency. It’s a public protocol so that every vendor can support MLAG by using their own custom rolled implementation of it. MLAG is the ability of two or more switches to act like a single switch when forming link bundles. It allows a host to uplink to two switches for physical diversity, while still having only one single bundle interface to manage. In turn, these two switches can connect to two other switches using MLAG, with all links forwarding.

In MLAG links, Link Aggregation Control Protocol (LACP, 802.3ad) is typically used to negotiate north and south between host and an MLAG virtual switch or between MLAG virtual switches. East and west proprietary protocols are used between switches that are members of the same MLAG virtual switch. Figure 1 shows the example of using multiple FS S5800-48F4S gigabit ethernet switches to form an MLAG Pair. With four leaf switches in an MLAG pair, you can build redundant connections from the server to the switches. The LAG groups can be formed using static link aggregation or LACP based negotiation methods.

What Is MLAG?

Figure 1: Using FS S5800-48F4S Switches to Form an MLAG Pair

Benefits of MLAG

 Traffic is evenly distributed to each of the switches through the use of LAG hashing.
 Simply bundle more links into the LAG to increase bandwidth for North & South as well as East & West
 Offers stability with dual management and control planes
 Able to upgrade one switch at a time without affecting other devices
 Expands port capacity freely–simply adding another switch East or West by creating another MLAG to another switch

What Is VPC?

VPC is short for Virtual Port Channel where a Port Channel is a regular LAG. It is Cisco Nexus specific protocol that you can’t configure it on any type of switch. VPC is a new technology with which you can connect one switch (access switch) to two uplink switches (distribution switch) and form an EtherChannel between them. VPC allows two physical devices to be logically paired together to present a common switching platform to connected to other remote devices. As illustrated below, VPC is utilized to create inter-switch links spanning two switches while keeping two control planes of these switches separate. After you enable the VPC function, you create a peer keep-alive link, which sends heartbeat messages between the two VPC peer devices. The VPC domain includes VPC peer devices, the VPC peer keep-alive link, the vPC peer link, and all the Port Channels in the VPC domain connected to the downstream device. You can have only one VPC domain ID on each device.

what is VPC

Figure 2: Form a VPC Pair by Creating Inter-switch Links

Benefits of VPC

 Allows a single device to use a Port Channel across two upstream devices
 Eliminates Spanning Tree Protocol blocked ports
 Provides a loop-free topology
 Uses all available uplink bandwidth
 Provides fast convergence if either the link or a device fails
 Provides link-level resiliency
 Helps ensure high availability

MLAG vs VPC: What’s the Difference

Both MLAG and VPC are aimed to create a port group between two switches. In MLAG or VPC domain, each switch is managed and configured independently and able to forward/route traffic without passing to a master switch. MLAG and VPC are similar to configure and operate. In general, MLAG setup is a bit easier than VPC, because many of the details are handled for the network operator when compared to the more granular fussiness of the VPC configuration. Thus network engineers who want to deploy VPC should study vendor’s scenario-driven VPC design guides before building a VPC domain.

Besides, MLAG mainly enables Layer 2 multipathing from the host to gain either additional bandwidth or link resiliency. While VPC can provide Layer 2 and Layer 3 multipathing, which allows you to create redundancy by enabling multiple parallel paths between nodes and load-balancing traffic where alternative paths exist.

MLAG vs VPC: FS Provides Both Solutions

FS.COM offers a wide portfolio of network switches with various port design and feature sets, including 10GbE switch, 25GbE switch, 40GbE switch and 100GbE switch. Some of them support the function of MLAG and VPC. The following diagram presents FS MLAG and VPC enabled network switch options.

MLAG Enabled Network Switches

All of FS N series and certain types of S series network switches are MLAG enabled devices with various design options, meeting your cabling requirement while delivering improved flexibility.

Switch
FS P/N
10Gb Switch
S5800-48F4S, S5800-8TF12S, S5850-32S2Q, S5850-48S6Q
40Gb Switch
S5850-48T4Q, N5850-48S6Q, N8000-32Q
100Gb Switch
S5850-48S2Q4C, S8050-20Q4C, N8500-48B6C, N8500-32C

VPC Enabled Network Switches

All of FS N series network switches are VPC enabled devices, the details of which are presented as follows.

FS P/N
N5850-48S6Q
N8000-32Q
N8500-32C
N8500-48B6C
Switch Class
Layer 3
Layer 3
Layer 3
Layer 3
Port Design
48*10GbE+6*40GbE
32*40GbE
32*100GbE
48*25GbE+6*100GbE
MLAG
Yes
Yes
Yes
Yes
VPC
Yes
Yes
Yes
Yes
VLAN
Yes
Yes
Yes
Yes
MPLS
Yes
Yes
Yes
Yes

Conclusion

Both MLAG and VPC are desirable implementations for data centers and cloud computing networks that require the highest level of network bandwidth and reliability. MLAG takes the benefits of link aggregation and spreads them across a pair of data center switches to deliver system level redundancy as well network level resiliency. And VPC is more suited to achieve non-blocking path diversity where virtual machines might reside at any given point. No matter which method you are deciding between MLAG vs VPC, the foremost thing is to make clear whether your networking devices can support MLAG or VPC. Then take account of the fabric architectures and your own specific traffic requirements before implementing a certain connection method.

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