A new site's gateway isn't able to form a tunnel to the existing site-to-site Internet Protocol Security (IPsec) virtual private network (VPN) device at headquarters. Devices at the new site have no…

Question

Options

• AEnable IPSec tunnel mode on the VPN devices at the new site and the corporate headquarters.
• BEnable Layer 2 Tunneling Protocol (L2TP) on the VPN devices at the new site and the corporate
• CEnable Point-to-Point Tunneling Protocol (PPTP) on the VPN devices at the new site and the
• DEnable Network Address Translation (NAT) - Traversal on the VPN devices at the new site and

• A
  23% (10)
• B
  5% (2)
• C
  12% (5)
• D
  60% (26)

Explanation

The best way to resolve the issue and get the remote site connected is to enable NAT-Traversal on the VPN devices at the new site and the corporate headquarters. NAT-Traversal is a technique that allows IPsec VPN devices to operate behind a NAT device, such as a router or a firewall, and establish a tunnel with another IPsec VPN device on the internet. NAT-Traversal encapsulates the IPsec packets in User Datagram Protocol (UDP) packets, and uses a special port (4500) to bypass the NAT device and reach the destination IPsec VPN device. NAT- Traversal solves the problem of IP address mismatch, as it allows the IPsec VPN devices to use their private IP addresses, rather than their public IP addresses, to communicate with each other. In this scenario, the new site's gateway has a private IP address (192.168.1.1) that is not routable on the internet, and the ISP gateway performs NAT to translate the private IP address to a public IP address. However, this causes the IPsec VPN device at the headquarters to reject the connection request from the new site's gateway, as it expects the public IP address of the new site's gateway to match the private IP address in the IPsec packet. By enabling NAT-Traversal on both VPN devices, the new site's gateway can use its private IP address to form a tunnel with the headquarters' VPN device, and the ISP gateway can pass the UDP packets without modifying the IP addresses. Enabling IPsec tunnel mode, L2TP, or PPTP on the VPN devices will not resolve the issue, as these are different protocols or modes that are not compatible with NAT-Traversal or IPsec. IPsec tunnel mode is a mode that encrypts both the IP header and the payload of the IP packet. L2TP is a protocol that creates a virtual private network at the data link layer. PPTP is a protocol that creates a virtual private network at the network layer.

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