Connecting a small site to multiple service providers can be extremely easy – you get two upstream links and two provider-assigned (PA) IPv4 addresses (static or dynamically assigned). Since each ISP will give you only a single IPv4 address, you have to use private IPv4 addresses on the LAN side of the router (Figure 1).

Most ISPs are unwilling to run a dynamic routing protocol with small sites, so you must configure static default routing on your router. Since you would almost always prefer one provider over the other, you would create a primary and a backup default route.