Posted on October 21, 2015 11:07 am
 |  Asked by Arthur Liew
 |  795 views
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Hi Guys,

Just want check how to configure Arista EOS to support the following

ToR1 —-ToR2

|               |

SW1 —- SW2

ToR1 & ToR2 are Arista MLAG pair to appear as single logical switch

SW1 & SW2 is access sw running STP protocol

Rgds

Art

 

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Posted by Alexis Dacquay
Answered on October 27, 2015 11:59 pm

Art,

Just to clarify, MLAG is a LAG technology (port-channel), it does not make the switches in their whole appear as a single logical switches. It only operates that logical unification for the port-channel : attached devices’ portchannel (static or LACP) would consider the Arista MLAG end point as a single LAG peer (albeit two physicals).

To be part of the same MLAG (multi-chassis LAG), the device or devices attached must present a single common LAG end point. It can be using a technology similar to MLAG for Layer2 Multipathing in port-channels, or a stacking technology, which both can present 2 physical devices as 1 LAG end point (although there are other considerations such as inter-link bottlenecks in stacking)

STP alone cannot do that.

 

Regards,

Alexis

 

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Posted by John Gill
Answered on October 31, 2015 3:51 am

Art,

As you mentioned, from your desire to act as 1 switch, if you are in an MLAG you run STP as if you were a single bridge.

It is important to note the MLAG peer link should never block, so your best choice in such a design would be to block between SW1 and SW2 (assuming all VLANs everywhere).

Regards,
John

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