You plan to deploy route-based Site-to-Site VPN connections between several on-premises locations and an Azure virtual network. Which tunneling protocol should ...

A Site-to-Site (S2S) VPN gateway connection is used to connect your on-premises network to an Azure virtual network over an IPsec/IKE (IKEv1 or IKEv2) VPN tunnel.
IKEv2 supports 10 S2S connections, while IKEv1 only supports 1.
Reference:
https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-howto-site-to-site-classic-portal
https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-connect-multiple-policybased-rm-ps