Refer to the exhibit.

For a site-to-site IPsec VPN, each peer must configure apre-shared keytied to thepublic IP address of the remote VPN peer:

crypto isakmp key address

From the diagram:

R1 outside IP:192.168.10.1/24

R2 outside IP:192.168.20.2/24← remote peer for R1

In the current R1 configuration, the ISAKMP key is incorrectly bound to192.168.10.2, which is a local next-hop/ISP address on R1’s own subnet, not the R2 public IP. Because the pre-shared-key address does not match the source IP of R2’s IKE packets, phase 1 negotiation fails and the tunnel never comes up.

The correct configuration on R1 must therefore be:

crypto isakmp key vpnuser address 192.168.20.2

Options A and C incorrectly change the default route (next hop must be the local ISP router, not R2’s public IP or a LAN address). Option D uses an internal address (10.1.1.2), which is not the IP used for IKE on the Internet.