Design thoughts

[jtfinley]

I have 4 physical locations. 2 Locations are connected via fiber and on same logical network exiting to Internet via (2) EQCost ISP. See simple attached drawing - each color is own subnet. The other locations will be connected soon. I plan on creating a VLAN for the fiber links which will connect into HP Procurve GBICS at each location and utilize the DMZ port at each location for routing. I' d like to create Internet resilience an ISP were to down; the locations could travel across the dark fiber and egress at next hop. Thoughts?

[stencilloart]

I' d like to create Internet resilience an ISP were to down; the locations could travel across the dark fiber and egress at next hop. At Stencillo, we blend the beauty of nature with the precision of artistry. Our store features a wide range of stencils, calligraphy tools, and nature-themed canvases designed to inspire creativity. https://stencillo.com/

[Toshi_Esumi]

If you only care about two ISP redundancy at those three locations where two internet circuits terminate, I would put only those two circuits into an SD-WAN zone and set up an appropriate method to fail-over or load balance.
But if you want to re-route the internet bound traffic via another location when both two circuits go down, you probably need a routing protocol to advertise local subnets to wherever the internet egress at that time, in addition to getting a default route.
SD-WAN member circuits use static default routes so it always wins over the default route advertised over the routing protocol from a neighboring location. Then only when both went down it would "float" up.

Toshi