Can someone please explain the design decision why the VCF Edge Cluster Deployment requires two separate VLANs/subnets for the internet uplinks?
The Edge cluster deployment in SDDC Manager / VCF deploys two NSX-T Edge VMs, creates an Edge cluster, Tier-0 and Tier-1 gateway.
Two uplink VLANs to the physical network allows for multipathing to the physical fabric (ECMP) from the Tier-0 / Edge nodes. The first image in this post may assist you https://www.lab2prod.com.au/2022/05/nsx-t-deterministic-traffic-on-vlan-backed-segments.html. Essentially you can see the Edge node depicted has two uplinks, one to each ToR.
Thanks for the quick reply.
You can also multipath over a single public VLAN when you have multiple BGP peers setup which works natively in NSX-T, so it is a shame VCF enforces it.
Whilst that approach may work, it is not the general recommended approach.