Layer2-extension using NDO/MSO for Active/Standby deployments

[SandevChopra07800]

Hi, we are doing ACI multi-site across 2 x customer DCs and one of the use cases is vm-mobility/layer-2 extension. Requirement is not to extend the layer-3(BD-subnet), as it should only remain in the primary site. This is to always use the primary site for all in-coming and out-going traffic for that vlan to maintain symmetric traffic-flows. How to deploy and achive this from the NDO? 

Thx

[jiarchen]

HI, 
Thank you for your questions. For this situation you could create a Stretch_Template which stretched across two sites for the vm-mobility/layer-2 extension use case. As for the layer-3 (BD subnet), you could create a template for each site seperatly to add Layer3 information, l3out configuration could also configured under site template which are not stretched.  Hope this could answer your questions. 
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[jmiguelhp]

Hello.

This works for different objects (bd1 -no subnet- in Stretched_Template, bd2 -w/subnet- in separate template) but I think the query refers to the same Bridge Domain. You cannot define the same object in different templates, also, I think you are not able to configure subnet in BD's "Site Local Properties".

There is an option to configure subnet in EPG's "Site Local Properties" but nodes in the other site are not able to reach it (works as GW only for local site).

@jiarchen Am I missing something?

@SandevChopra07800 did you accomplish something?

As far I can say, there is no way to perform this in NDO

Thanks!

[Robert Burns]

This isn't possible to define a stretched BD (L2 Domain) but only have the BD SVI defined on one site.  If you'd like to keep one of the sites as your Ingress/Egress point for both fabrics you can simply stretch the BD and SVI to both sites, then apply an inter-site L3out only for the Primary DC.  This would allow resources in the secondary site to transit via the Primary site to enter/leave both fabrics.  There's likely a larger design discussion to be had.  The benefit of multisite is you can operate conistent L3outs for each site, then in the event of a failure leverage a remote site's L3out.   Have a look at https://www.cisco.com/c/en/us/support/docs/software/aci-data-center/217597-configure-intersite-l3out-with-aci-multi.html 
The design you're describing makes the primary site a single point of failure for BOTH fabrics.  Multisite's strength is that it provides Active/Active sites for both L2/L3 mobility - each site inclusive of their own redunancies & resiliencies.  

Robert