In Cisco IOS site-to-site IPsec VPN configurations using crypto maps, the set peer command must define the reachable, public IP address of the remote VPN gateway. The ISAKMP and IPsec security associations are negotiated with this specific address. According to the provided network topology, router R1 must establish an IPsec tunnel with router R2 across the intermediate Internet cloud. R2's external, routable interface IP address is 192.168.20.2. The current configuration on R1 mistakenly defines the peer as 10.2.0.2, which is an address residing in the private, internal subnet of Site 2. Issuing the command set peer 192.168.20.2 on R1 correctly directs the tunnel establishment messages to R2's public-facing interface, resolving the issue.

A. set peer 10.1.0.1 targets an address on R1's own internal LAN (Site 1), failing to reach the remote gateway over the Internet cloud.

C. set peer 192.168.10.1 targets R1's own external interface address. A router cannot establish a site-to-site IPsec tunnel with its own local interface as the remote peer.

D. set peer 10.2.0.1 targets an internal, non-routable private IP address in Site 2's LAN, which the Internet cloud cannot natively route to for initial tunnel establishment.

Cisco Systems, Inc. Cisco IOS Security Configuration Guide: Secure Connectivity, Release 15M&T. Section: "Configuring IPsec Network Security," Subsection: "Creating Crypto Maps." (Details the requirement that the set peer command must specify the IP address or hostname of the remote IPsec peer's terminating interface).

Cisco Systems, Inc. (n.d.). IPsec VPN Design Guide. Section: "Site-to-Site VPN Overview." (Explains the necessity of using routable WAN addresses for the establishment of IKE/IPsec tunnels across a transit network like the Internet).