ACI Back to Back VRF

[JPC11]

Hi,

I have installed and configured ACI at one of our data centres and I now need to do the same at our secondary data centre using the back to back setup rather than IPN.  I was planning on connecting the spines up to our WAN routers and wondered if the best practice, would be to make use of a separate VRF for the ACI traffic rather than just lump all the ACI and other cross site traffic together.

I appreciate any replies.

Jonathan

[RedNectar]

Hi @JPC11 ,

To deploy two ACI fabrics in a "back-to-back" configuration, the Spines at each site need to form OSPF adjacencies with each other. This means you need L2 connectivity between the sites - dark fibre is the best option

If you want to put a router in the picture, you'll have to make that router provide some kind of L2 service between the sites - a L2 EVPN.

Probably easier to create an IPN! [Edit](Oops - I mean ISN. Same animal, different spelling)[/Edit]

[JPC11]

Thank you both for your help here.  I did reply via email last week but I have just noticed that all the text was removed.

Thanks again for taking the time to help.

[Robert Burns · Accepted solution]

I will whole heartidly agree with Chris that you should also try to build a proper ISN.  You mentioned separate fabrics, so this would imply Multisite.  Though B2B is a supported topology, you're limited to 2 sites and you lose the ability to ever expand to the public cloud (GCP/AWS/Azure).  Even if you don't plan on expanding like this today, I'd recommend not painting yourself into a corner by doing B2B.  You mention you already have WAN routers, well that can be your ISN!  Just carve out a separate VRF on it and connect everything together.  You'll need to support jumbo MTU between the sites (>1600b) and few other considerations, but most platforms will support what a Multisite ISN requires.  Multisite also handles all the policy stretching and consistency between your fabrics which saves you having to manually stitch policies together (very messy).  

Robert