Hub connection: many-to-one

In this example, Site 1 has two Internet connections, while the Hub has only a single one. With the BGP on loopback design, we can configure a single Dial-Up IPsec endpoint on the Hub to which the Spoke will establish two static IPsec tunnels.

Remember that, unlike with the traditional BGP per overlay design, we no longer need to configure tunnel subnets, and this is why the same Spoke can establish multiple IPsec tunnels towards the same Dial-Up endpoint without tunnel subnet conflicts. We also do not need to configure additional BGP sessions, since there is always a single session between the Spoke and the Hub.

The IKE exchange-ip-addrv4 feature will inject the /32 loopback route through both of the established tunnels, allowing the BGP routes to be recursively resolved through all available overlay paths.

This topology cannot be built with the BGP per overlay design. Each static IPsec tunnel in that design must be connected to its own Dial-Up endpoint, with its own tunnel IP, towards which a separate BGP session would be established. For this reason, in a similar scenario using BGP per overlay design, two separate Dial-Up IPsec endpoints would be required on the Hub, and both would be terminated on the same Internet connection.