Posted on July 15, 2016 2:37 pm
 |  Asked by Wasfi Bounni
Print Friendly, PDF & Email


Can you have MLAG without Stateful Switch Over What exactly the advantage of MLAG with SSO VS MLAG without SSO?

For SSO to be functional, do you need to have the exact software image on both peers?

Posted by Lokesh Charora
Answered on July 24, 2016 4:18 am

MLAG and SSO are 2 different concepts:

MLAG: Arista switches support Multi-Chassis Link Aggregation (MLAG) to logically aggregate ports across two switches.High availability data center topologies typically provide redundancy protection at the expense of oversubscription by connecting top-of-rack (TOR) switches and servers to dual aggregation switches. In these topologies, Spanning Tree Protocol prevents network loops by blocking half of the links to the aggregation switches. This reduces the available bandwidth by 50%.  Deploying MLAG removes oversubscription by configuring an MLAG link between two aggregation switches to create a single logical switching instance that utilizes all connections to the switches. MLAG provides Active-Active Layer-2 redundancy.


SSO: On modular switches with redundant supervisor modules, control of the switch can be transferred to the standby supervisor to minimize downtime and data loss in the case of a reset, reload, or failure of the active supervisor. How the switchover takes place is determined by the redundancy protocol on the active supervisor.In stateful switchover (SSO) protocol, the switch synchronizes both startup-config and running-config files between the supervisor modules and fully boots the standby module to a “standby hot” state to speed the switchover process and minimize packet loss. If the active supervisor fails, or a manual switchover is initiated, the standby supervisor immediately becomes active, and running state is maintained. An SSO switchover is transparent from the outside.

You can have Mlag without SSO. Let me know if above write-up answers your question.

Posted by jp
Answered on September 15, 2016 10:46 am

To perhaps add a further dimension – a pair of switches in an MLAG configuration provides a naturally highly available path for the downstream device/host. It is not necessary to have further ’in-box’ redundancy as both MLAG peers are active anyway.

MLAG also supports ISSU (In Service Software Upgrade) – thus allowing each MLAG peer to be individually upgraded without the need to take down the entire port-channel towards the connected device.

Hope this helps,


Post your Answer

You must be logged in to post an answer.