GRE with HSRP

Hello together.

I have a question about routing in a network.

The network looks like this: https://imgur.com/a/Y6rNuur

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So R1 and R2 are configured with HSRP. Outside ip address is 10.0.0.1

The outside adress of the other router is 20.0.0.1.

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Now I have configured GRE-Tunnels on R1, R2 and R3 with the IPs from Subnet 172.16.1.0/24

How should the Multilayer Switch be configured that the routers know each other tunnel address and reach their VPN destination (10.0.0.1 and 20.0.0.1)

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